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NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 2

NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 2

Differences between gasoline, diesel, and jet fuel

Gasoline is a fuel made from crude oil and other petroleum-based liquids, containing carbon numbers generally between 4 and 12, and exhibiting boiling points of up to 120 °C. Gasoline is primarily used as a fuel for vehicles. Petroleum refineries and blending facilities produce motor gasoline for sale at gas (or petrol) stations. Most of the gasoline that petroleum refineries produce is unfinished gasoline. This unfinished product requires blending with other liquids to control parameters such as octane rating and volatility to make gasoline meet the basic requirements for fuel that is suitable for use in spark ignition engines.

Diesel fuel is refined from crude oil at petroleum refineries. «Diesel» is the common term for the petroleum distillate fuel oil sold for use in motor vehicles that use the compression ignition engine, invented by the German engineer Rudolf Diesel (1858–1913). He patented his original design in 1892. One of the fuels that Rudolf Diesel originally considered for his engine was vegetable seed oil, an idea that eventually contributed to the biodiesel production process of today. Prior to 2006, most diesel fuel contained high quantities of sulfur. Sulfur emissions from combusting diesel fuel leads to air pollution that is quite harmful to human health. Therefore, the U.S. Environmental Protection Agency issued requirements to reduce the sulfur content of diesel fuel to be as low as 15 mg/L. Diesel fuel contains components with a carbon number range from 8 to 21 (though mainly between 16–20) and is the fraction that boils between 200 °C and 350 °C.

Jet fuels (or aviation fuels) are one of the basic products used by aircraft. Jet fuel is comprised of refined petroleum products with carbon numbers between 10 to 16 (although they can range from 6 to 16), and it boils between 150 °C and 275 °C. This type of fuel is heavily regulated by national and international bodies. There are two main types of jet fuel: Jet A and Jet B. The main difference between the two is the freezing point. Jet B is usually used for military operations and locations with inclement weather. Jet A is mainly used to fuel commercial airplanes.

Near-infrared spectroscopy—an ASTM compliant tool to assess the quality of gasoline, diesel, and jet fuel

Near-infrared spectroscopy (NIRS) has been an established method for both fast and reliable quality control within the petrochemical industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.

There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.

In the remainder of this post, available turnkey solutions for gasoline, diesel, and jet fuel are outlined which have been developed according the NIRS implementation guidelines of ASTM E1655 (method development), ASTM D6122 (method validation), and ASTM D8340 (results validation). Afterward is a discussion about the return on investment (ROI) of using NIRS as an alternative to the CFR Engine.

Did you miss Part 1 in this series about NIRS as a QC tool for the petrochemical industry? Check it out below!

Read our previous blog posts to learn more about NIRS as a secondary technique.

NIRS expedites and simplifies fuel quality control

 Without high quality fuels (e.g., gasoline, diesel, and jet fuel), our daily lives would look much different. At the end of the production process as well as at various steps in the distribution chain, the quality of the product needs to be determined. Typically, key quality parameters such as RON/MON (research and motor octane numbers), cetane index, and flash point are determined in the laboratory by chemical and physical methods. These methods not only incur high running costs but they are also quite time consuming.

NIRS on the other hand requires neither chemicals nor sample preparation. This technique can even be used by non-technical people (no chemistry degree necessary) and it provides results in less than a minute. Furthermore, multiple chemical and physical parameters can be determined simultaneously. The combined benefits of this technology make NIRS the ideal solution for many daily QA/QC measurements or ad-hoc at-line analysis.

Metrohm offers the NIRS DS2500 Petro Analyzer for quality control and routine analysis of fuels and is compliant with ASTM D6122. Resistant to dust, moisture, and vibrations, this instrument is not only suitable for laboratory use, but also use in direct production environments. Learn more on our website

Turnkey solutions: available pre-calibrations for gasoline, diesel, and jet fuel

Table 1 lists all constituents covered by the pre-calibrations for these different fuels. Click on the fuel type in the table to learn more about its pre-calibrations offered by Metrohm.

Table 1. Pre-calibrations available for a variety of key quality parameters in gasoline, diesel, and jet fuel.
Fuel type Parameters Range SECV
Gasoline RON 81–100 0.68 0.958
MON 81–88 0.53 0.889
Anti-Knock Index 85–94 0.45 0.948
Aromatics 20–45% 0.011 0.959
Benzene 0.15–0.70 % 0.0004 0.902
Density 0.74–0.76 g/cm3 0.0024 g/cm3 0.797
Olefins 0–25 % 0.013 0.909
Oxygen 0.2–2.0 % 0.00045 0.994
Diesel Cetane index 46–77 0.62 0.987
Cetane number 45–60 0.942 0.942
Density 0.82–0.89 g/cm3 0.0021 g/cm3 0.968
CFPP -22–(+19) °C 2.8 °C 0.963
T95 325–410 °C 7.04 °C 0.799
Flash Point 56–120 °C 2.7 °C 0.97
Viscosity 2–5.5 cSt 0.15 0.91
Kerosene / Jet Fuel Cetane index 36–50 1.1 0.871
API gravity 38–48 ° 0.56 ° 0.931
Aromatics 10–25 % 0.01 0.851
T10 158–200 °C 4.1 °C 0.801
T20 165–205 °C 3.1 °C 0.88
T50 180–220 °C 4.1 °C 0.789
Density 0.78–0.83 g/cm3 0.003 g/cm3 0.936
Flash Point 38–65 °C 4.3 °C 0.62
Freeze Point -65–(-40) °C 3. 5°C 0.576
Hydrogen 13.2–14.2 % 0.0005 0.934
Saturates 75–90 % 0.009 0.888
Viscosity at 20 °C 3–7 cSt 0.33 cSt 0.804

Learn more about the possibilities of petrochemical analysis with Metrohm NIRS DS2500 Analyzers in our free brochure.

Application example: quality control of diesel with the NIRS DS2500 Petro Analyzer

The cetane index (ASTM D613), flash point (ASTM D56), cold filter plugging point (CFPP) (ASTM D6371), D95 (ISO 3405), and viscosity at 40 °C (ISO 3104) are among some of the key parameters to determine the quality of diesel. The primary test methods for these parameters are labor intensive and challenging due to the need for multiple analytical methods.

In this turnkey solution, diesel samples were measured in transmission mode with a NIRS DS2500 Petro Analyzer over the full wavelength range (400–2500 nm). The built-in temperature-controlled sample chamber was set to 40 °C to provide a stable sample environment. For convenience reasons, disposable vials with a pathlength of 8 mm were used (Figure 1), which made a cleaning procedure unnecessary.

Figure 1. Quality control of diesel fuel as performed by the Metrohm NIRS DS2500 Petro Analyzer.

The obtained Vis-NIR spectra (Figure 1) were used to create prediction models for the determination of key diesel parameters. The quality of the prediction models was evaluated using correlation diagrams which display the correlation between Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis (Figure 2).

Figure 2. Correlation plots and figures of merit (FOM) for the different constituents tested in diesel.

This solution demonstrates that NIRS is excellently suited for the analysis of multiple parameters in diesel fuel, providing results in less than one minute without the need for sample preparation or any chemical reagents.

Want to learn more? Download our free Application Note.

Return on investment: CFR Engine vs. NIRS

Gasoline requires intensive checks on several quality parameters which must be within certain specifications before commercialization. These parameters which can also be controlled by NIRS analysis include the research octane number (ASTM D2699) and motor octane number (ASTM D2700), also known as RON/MON.

The importance of measuring these values precisely is not only to comply with regulations, but also because of the further potential to save costs for manufacturers. As an example, RON values exceeding the stated requirements will still be accepted by the market, but these products will then include a higher amount of lucrative long-chain organic molecules. This so-called «RON giveaway» is estimated at approximately 0.5 RON per barrel, resulting in $2.25 million USD/month in lost revenue for a production process of 100,000 barrels per day.

Figure 3. CFR® F1/F2 Octane Rating Unit Combination Research & Motor Method. (Source: CFR Engines Inc.)

The Combination Cooperative Fuel Research (CFR) octane rating engine (model F1/F2) is used to determine the octane quality of gasoline and fuel blending components. This unit is recognized and approved by ASTM D2699 and D2700. The engine is equipped with a heavy-duty crankcase, variable compression cylinder, carburetor with adjustable fuel to air ratio, and knock measurement equipment (Figure 3).

Ready-to-use NIRS systems are also available for monitoring several gasoline quality parameters which cover varied ranges and their respective precisions (Table 1). Additionally, the manufacturers of NIRS analyzers usually offer application support to extend these ranges or improve upon the precision.

An overview of estimated costs for the analysis of RON and MON with a CFR Engine compared to the Metrohm NIRS DS2500 Petro Analyzer is shown in Table 2. The full payback is achieved within two years if considering only 50% of the primary analysis method (CFR Engine) is replaced by NIRS. This calculation is based on 2000 analyses per year (1000 RON + 1000 MON), with total running costs of approximately $32.50 per analysis (chemicals, maintenance, and labor).

Table 2. Cost of ownership CFR engine vs. DS2500 Petro Analyzer.
Total analyses RON + MON per year 2000 2000
Cost of operator per hour $25.00 $25.00
Cost of Analyzer CFR Engine NIRS DS2500 Petro Analyzer
Analyzer $500,000.00 $55,000.00
Total initial costs $0.001 $55,000.00
Running costs consumables / chemicals / maintenance
Chemicals per year (ASTM D2699/D2700) $20,000.00 $0.00
Maintenance cost per year $20,000.00 $1,500.00
Chemicals plus maintenance cost per analysis $20.00 $0.75
Total running costs per year $40,000.00 $1,500.00
Time spent per analysis  30 minutes < 1 minute
Labor cost of 1000 analyses of RON (ASTM D2699) $12,500.00 $416.50
Labor cost of 1000 analyses of MON (ASTM D2700) $12,500.00 $416.50
Labor cost per analysis $12.50 $0.42
Total labor costs per year $25,000.00 $833.00
Total running costs per year $65,000.00 $2,333.00
1Assumption that the instrument had previously been purchased, and therefore this cost is not included in the ROI calculation.

More information about the analysis of RON/MON and other parameters in gasoline can be found in our free Application Notes below.

In this example, RON/MON analysis was used to show cost savings and ROI when using NIRS to supplement a primary method. However, when expanding this to consider other key quality parameters such as the ones indicated in Table 1, the financial incentives for such an investment are even more compelling.


Near-infrared spectroscopy is very well suited for the analysis of key quality parameters in gasoline, diesel, and jet fuel. Available pre-calibrations are developed and validated in accordance with the ASTM guidelines. Positive aspects of using NIRS as an alternative technology are the short time to result (less than one minute), no chemicals or other expensive equipment needed, and ease of handling so that even shift workers and non-chemists can perform these analyses in a safe manner.

Future installments in this series

This blog article was dedicated to the topic of gasoline, diesel, and jet fuel and how NIR spectroscopy can be used as the ideal QC tool for the petrochemical / refinery industry. Future installments will be dedicated to other important applications in this industry. These topics will include:


  • Pyrolysis gasoline (Pygas)
  • Lubricants
  • ASTM Norms

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.
Spectroelectrochemistry: shedding light on the unknown

Spectroelectrochemistry: shedding light on the unknown

The combination of two well-known analytical techniques, electrochemistry and spectroscopy, gives rise to spectroelectrochemistry (SEC), an established scientific methodology. This hybrid technology combines the advantages of each technique, offering the best of both worlds [1]. The word «spectroelectrochemistry» is the result of combining these two terms as two pieces of a puzzle that fit perfectly together.

In this article, written for both beginners in the field as well as more experienced readers, we focus on introducing this technique from its beginnings to its advantages in research, and then discuss new systems and solutions that will make it easier to work on the multitude of applications that spectroelectrochemistry can offer. 

Shedding light, in the literal sense of the phrase, on electrochemical knowledge and procedures. Spectroelectrochemistry offers analysts more information by being able to record both an optical and an electrochemical signal at the same time to obtain new data.

This is a multi-response method—it studies the process of electrochemical reactions with simultaneous optical monitoring. Spectroelectrochemistry provides two individual signals from a single experiment, which is a very powerful feature to obtain critical information about the studied system. Moreover, the autovalidated character of spectroelectrochemistry confirms the results obtained by two different routes. Find out more about this topic by downloading our free Application Note below.

Spectroelectrochemistry allows researchers to collect molecular, kinetic, and thermodynamic information from the reactants, intermediates, and/or products involved in electron transfer processes. Thus, it is possible to perform spectroelectrochemical studies on a broad range of molecules and different processes including: biological complexes, polymerization reactions, nanomaterial characterization, analyte detection, corrosion mechanisms, electrocatalysis, environmental processes, characterization of memory devices, and much more!

Ultimately, different kinds of information is obtained depending on the spectral range used. UV-VIS spectroscopy provides molecular information related to the electronic levels of the molecules, the NIR region provides data associated with the vibrational levels, and the Raman spectrum provides very specific information about the structure and composition of the sample due to the fingerprinting characteristics of this technique.

Electromagnetic Spectrum
Diagram of the electromagnetic spectrum.

The beginnings of spectroelectrochemistry

Theodore Kuwana, Ph.D. in chemistry and specialist in spectroelectrochemistry, bioelectroanalytical chemistry and modified electrodes.

This analytical technique was developed in the 1960’s, and became popularized by Professor Theodore Kuwana and other researchers [2]. They had begun to work with transparent electrodes to study a simultaneous process—measuring the charge and absorbance (at the same time) when a beam of light passes through the electrode. As a result, they developed transparent electrodes and this marked the beginning of concurrent electrochemical and UV-VIS absorption measurements.

These so-called «optically transparent electrodes» (OTEs) were developed to carry out the combination of optical and electrochemical experiments. Some of the most commonly used OTEs began as oxide doped with antimony on glass, then developed into different thin films of gold or platinum on quartz, followed by germanium electrodes for IR wavelengths, as well as pure gold and platinum micromeshes (where the holes provide the required transparency to light). However, not all spectroelectrochemical configurations require transparent electrodes. For more information, download the electrode reference flyers from Metrohm DropSens to properly work with the different spectroelectrochemical techniques.

A selection of Metrohm DropSens references. Left: C013 for in-situ surface Raman spectroscopy. Right: P10 optically transparent and specially designed for spectroelectrochemical applications.

Download the free flyers for these electrodes below for further information.

The first published paper on spectroelectrochemistry [2], in which Dr. Kuwana participated, describes the use of tin oxide-coated glass surfaces (optically transparent electrodes) for following the absorbance changes of different electroactive species during electrolysis. Since then, the number of works and investigations based on this technique have grown steadily.

Spectroelectrochemistry publications have increased significantly since its discovery in the 1960’s (results of searching «Spectroelectrochem*» as a term in Scopus as of June 2021).

Take a look for yourself to see how things have changed in the last several decades!

An array of spectroelectrochemical techniques to choose from

The following graphic is classified according to the combination of different electrochemical and spectroscopic methods. The general classification is based on the spectroscopic technique: ultraviolet (UV), visible (Vis), photoluminescence (PL), infrared (IR), Raman, X-ray, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR).

Spectroelectrochemistry (SEC) is the combination of spectroscopy and electrochemistry.

In recent years, significant advances have occurred regarding the design, development, and possibilities offered by instruments for working with spectroelectrochemical techniques. Also, the assemblies and the connections between products and accessories that facilitate the use of this equipment have improved in recent decades, contributing to make research and experiments in this field easier and more affordable.

The evolution of spectroelectrochemical instrumentation

Traditionally, the configuration for spectroelectrochemical analysis consists of two instruments: one spectroscopic instrument and the other for electrochemical analysis. Both instruments are connected independently to the same spectroelectrochemical cell and are generally not usually synchronized. In addition, each instrument is controlled by a different (and specific) software in each case, so two programs are also needed to interpret each signal and yet another external software for the processing and analysis of the data obtained by the first two programs. Finally, it must be considered that synchronization is not guaranteed, making the performance of experiments and tests with this configuration slow, complex, and costly.

This detached spectroelectrochemical setup displays the complexity of various software and programs used, showing that different systems are not able to obtain actual synchronized electrochemical measurements and data (click to enlarge).

Metrohm DropSens took this opportunity to create something that did not exist before—a revolution in the state-of-the-art of spectroelectrochemistry: the SPELEC line of instruments which are fully integrated, synchronized solutions that offer much more versatility to researchers. The devices include all of the components needed to work with spectroelectrochemical techniques in a simple way and in a single system with a (bi)potentiostat/galvanostat, the light source, and the spectrometer (depending on the selected spectral range).

Find out more about SPELEC, the next-generation tool for spectroelectrochemical research on our website.

The SPELEC systems from Metrohm DropSens consist of one device and one software—a fully integrated, easy to use, practical setup for researchers.

These designs and configurations simplify the work, processes, and spectroelectrochemical measurements as well because only a single system and a single software are needed. In the case of the SPELEC solution, its advanced dedicated software (DropView SPELEC) is a specific program that controls the instrument, obtains the electrochemical and spectroscopic signals simultaneously, and also allows users to process and analyze the data together in a single step. It’s really that simple!

The future of spectroelectrochemistry: SPELEC systems and software

One instrument and one software: Metrohm DropSens SPELEC has everything you need for your spectroelectrochemical experiments while saving laboratory space and valuable time. SPELEC instruments offer the combinations of electrochemistry and UV-Vis, Vis-NIR, or even Raman spectroscopy in a single measurement with several different instrument options available (see below). Everything is integrated which allows more tests in less time, multiple spectra, a full range of accessories, and research flexibility with the different configurations available.

Several options are available depending on the spectral range needed:

SPELEC: 200–900 nm (UV-VIS)
SPELEC NIR: 900–2200 nm
SPELEC RAMAN: 785 nm laser
(other wavelengths available upon request)
SPELEC 1050: 350–1050 nm (VIS-NIR)

DropView SPELEC is a dedicated and intuitive software that facilitates measurement, data handling, and processing. With this program, you can display electrochemical curves and spectra in real time and follow your experiments in counts, counts minus dark, absorbance, transmittance, reflectance, or Raman shift. As far as data processing is concerned, DropView SPELEC offers a wide variety of functions including graph overlay, peak integration and measurement, 3D plotting, spectral movie, and more.

Testimonial from the University of Burgos on the integrated SPELEC system from Metrohm DropSens.

SPELEC instruments are very versatile, and although they are dedicated spectroelectrochemical instruments, they can also be used for electrochemical and spectroscopic experiments. They can be used with any type of electrodes (e.g., screen-printed electrodes, conventional electrodes, etc.) and with different spectroelectrochemical cells. Optical and electrochemical information is obtained in real time/operando/dynamic configuration. The main advantages of spectroelectrochemical techniques can be summarized as follows:

  • they simultaneously provide information obtained by two different techniques (electrochemistry and spectroscopy) in a single experiment
  • qualitative studies and quantitative analyses can be performed
  • high selectivity and sensitivity
  • spectroelectrochemistry is used in a wide variety of different fields due to its great versatility
  • new configurations facilitate the performance of spectroelectrochemical experiments, saving time, samples, costs, etc.

Learn more about the next-generation tool for spectroelectrochemical research on our website!

SEC analysis techniques: suitable for multiple applications

The characteristics of spectroelectrochemistry allow the constant development of new and broad applications in several different fields. Read on below to discover the capabilities of this technique.

Materials science: characterization of specific properties of carbon materials, quantum dots, composites, nanoparticles, Janus materials, polymers, as well as stability studies, determination of photochemical properties, development of new materials, etc.

For more information, download our free related Application Note below.

Sensing: selective and sensitive detection, rapid quantification of a huge variety of analytes, diagnostic tool, development of new methodologies and sensors, etc. [3].

Organic and inorganic chemistry: study of the properties and structure of different compounds, analysis of kinetic reactions, determination of electron transfer capacity, etc. [4].

Corrosion: evaluation of protective films as corrosion inhibitors, determination of electrode stability and reversibility, monitoring of layer and sublattice generation, improvement of protective properties of coating materials, etc.

Energy storage: monitoring of exchange and discharge cycles, determination of oxidation/reduction levels, characterization of new electrolytes for batteries, understanding of doping and splitting processes in solar cells, etc.

Electrocatalysis: characterization and comparison of the electrocatalytic activity of different catalysts, identification of intermediate species and their structural changes, elucidation of the reaction mechanism, etc. [5].

Life sciences: study of biological processes, characterization of molecules used in biotechnology, biochemistry or medicine, determination of antioxidant activity, etc.

Environment: identification and quantification of pesticides, dyes, and pollutants, monitoring of degradation and filtration processes, etc. [6]

Download our free related Application Note for more information.

Others: characterization of new materials for memory devices, comparison of minerals, identification of pigments, oils, and pastes, etc.

Learn even more about spectroelectrochemistry (SEC) and what it can do for your research by downloading our free brochure.

Contact us

to discuss how spectroelectrochemistry can boost your research.


[1] Kaim, W.; Fiedler, J. Spectroelectrochemistry: The Best of Two Worlds. Chem. Soc. Rev. 2009, 38 (12), 3373. doi:10.1039/b504286k

[2] Kuwana, T.; Darlington, R. K.; Leedy, D. W. Electrochemical Studies Using Conducting Glass Indicator Electrodes. Anal. Chem. 1964, 36 (10), 2023–2025. doi:10.1021/ac60216a003

[3] Martín-Yerga, D.; Pérez-Junquera, A.; González-García, M. B.; Perales-Rondon, J. V.; Heras, A.; Colina, A.; Hernández-Santos, D.; Fanjul-Bolado, P. Quantitative Raman Spectroelectrochemistry Using Silver Screen-Printed Electrodes. Electrochimica Acta 2018, 264, 183–190. doi:10.1016/j.electacta.2018.01.060

[4] Perez-Estebanez, M.; Cheuquepan, W.; Cuevas-Vicario, J. V.; Hernandez, S.; Heras, A.; Colina, A. Double Fingerprint Characterization of Uracil and 5-Fluorouracil. Electrochimica Acta 2021, 388, 138615. doi:10.1016/j.electacta.2021.138615

[5] Rivera-Gavidia, L. M.; Luis-Sunga, M.; Bousa, M.; Vales, V.; Kalbac, M.; Arévalo, M. C.; Pastor, E.; García, G. S- and N-Doped Graphene-Based Catalysts for the Oxygen Evolution Reaction. Electrochimica Acta 2020, 340, 135975. doi:10.1016/j.electacta.2020.135975

[6] Ibáñez, D.; González-García, M. B.; Hernández-Santos, D.; Fanjul-Bolado, P. Detection of Dithiocarbamate, Chloronicotinyl and Organophosphate Pesticides by Electrochemical Activation of SERS Features of Screen-Printed Electrodes. Spectrochim. Acta. A. Mol. Biomol. Spectrosc. 2021, 248, 119174. doi:10.1016/j.saa.2020.119174

Post written by Dr. David Ibáñez Martínez (Product Specialist Spectroelectrochemistry) and Belén Castedo González (Marketing and Communication) at Metrohm DropSens, Oviedo, Spain.

NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 1

NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 1

Introduction to the petrochemical and refining industry

Oil and gas for fuel are produced in nearly every corner of the globe, from small private wells generating around 100 barrels a day, to the large bore wells producing upwards of 40 times that volume. Despite this great variation in size, many parts of the refining process are quite similar.

Chemicals derived from petroleum or natural gas, so-called «petrochemicals», are an essential part of the contemporary chemical industry. The field of petrochemistry became increasingly popular around the early 1940’s during the second world war. At that time there was a growing demand for synthetic products which was a great driving force for the development of petrochemical products.

Oil refining aims to provide a defined range of products according to agreed specifications. Simple refineries use a distillation column (Figure 1) to separate crude oil into different fractions based on their chemical properties, and the relative quantities are directly dependent on the crude oil used. Therefore, it is necessary to obtain a range of crudes that can be blended into a suitable feedstock to produce the required quantity and quality of end products.

The basic products from fractional distillation are shown in Figure 1.
Wallace Carothers, inventor of polyamide.
Figure 1. Illustration of a fractionating distillation column used for the purposes of refining crude oil into several desirable end products.
Near-infrared (NIR) spectroscopy is a technique that is particularly suited for making quality control of these end products more efficient and cost-effective for manufacturers. Furthermore, NIRS is recognized and accepted by ASTM as an alternative method to other techniques. Dedicated ASTM methods for method development, method validation, and results validation are presented later in this article.

Read on for a short overview on NIR spectroscopy followed by application examples for the petrochemical and refinery industry to learn how petrochemical producers and refineries alike can benefit from NIRS.

NIR technology: a brief overview

The interaction between light and matter is a well-known process. Light used in spectroscopic methods is typically not described by the applied energy, but in many cases by the wavelength or in wavenumbers.

A NIR spectrometer such as the Metrohm NIRS DS2500 Petro Analyzer measures this light-matter interaction to generate spectra such as those displayed in Figure 2. NIRS is especially sensitive to the presence of certain functional groups like -CH, -NH, -OH, and -SH. Therefore, NIR spectroscopy is an ideal method to quantify different QC parameters like water content (moisture), cetane index, RON/MON (research and motor octane numbers), flash point, and cold filter plugging point (CFPP), just to name a few. Furthermore, the interaction is also dependent upon the matrix of the sample itself, which also allows the detection of physical and rheological parameters like density and viscosity.

Figure 2. Diesel spectra resulting from the interaction of NIR light with the respective samples.
All of this information is contained in a single spectrum, making this method suitable for quick multiparameter analysis. Liquid samples such as oils are secured within an appropriate container or vial (Figure 3), then placed as-is on the smart vial holder.
Figure 3. Liquid sample placement for NIR spectra measurement on the smart vial holder from Metrohm.
The measuring mode is referred to as «transmission», generally an appropriate procedure for analyzing liquids. For transmission measurement (Figure 4), the NIR light will travel through the sample while being absorbed. Unabsorbed NIR light passes to the detector. In less than 60 seconds the measurement is completed and the results are displayed.
Figure 4. A. Measurements of liquids are typically done with disposable vials. B. The NIRS measurement mode is known as transmission, where light travels through the sample while being absorbed (from left to right in the illustration).
The procedure to obtain NIR spectra already highlights two major advantages of NIR spectroscopy compared to other analytical techniques: simplicity regarding sample measurement, and speed:

  • Fast technique with results in less than a minute.
  • No sample preparation required – measure samples as-is.
  • Low cost per sample – no chemicals or solvents needed.
  • Environmentally friendly technique – no waste generated.
  • Non-destructive – precious samples can be reused after analysis.
  • Easy to operate – inexperienced users are immediately successful.

Read our previous blog posts to learn more about NIRS as a secondary technique.

Where can NIRS be used in the refining process?

The refining process can be divided into three different segments:

  • Upstream
  • Midstream
  • Downstream

Upstream describes the process of converting crude oil into intermediate products. Refineries are usually very large complexes with several hazardous explosive areas. Therefore, operators are reluctant to transport samples from the different processes to the laboratory. Even the process of obtaining samples for analysis at external QC laboratories is laborious and can require significant paperwork and certified transport services. For obvious reasons, in most cases inline measurements are preferred. These types of measurements are typically done by process NIRS analyzers.

Read more about the difference between atline, online, and inline analyses in our blog post.
Curious about NIRS analyzers for inline process measurements, even in explosive areas? Visit our website to learn more.
Midstream, shown here in Figure 5, offers many more opportunities for the Metrohm DS2500 Petro Analyzer to assist in quality control.
Figure 5. Flowchart of how crude oil becomes gasoline at the local gas station, and where NIRS can perform quality checks during the process.
Fuel is constantly checked for quality when it is received as well as supplied, and in addition to this many terminals also test fuel quality prior to offloading the trucks. The total time for receiving and offloading fuel into a storage tank is approximately 30 minutes, so a fast analysis technique like NIRS is very advantageous.

Downstream at fuel depots and gas stations, the regulatory agencies require measurement of many of the same quality parameters as in the production of gasoline and diesel, and this can also be accomplished with NIRS. There is a significant advantage if the analysis can be done on-site using fresh samples and without the hassle of needing to transport them to testing laboratories.

Mobile NIRS fuel testing using the Metrohm NIRS XDS RapidLiquid Analyzer (XDS-RLA) has been successfully implemented in a number of countries where they enjoy the benefits of having instantaneous on-site results for gasoline and diesel testing. The calibrations developed on the XDS-RLA are easily transferrable to the DS2500 Petro Analyzer. The DS2500 Petro Analyzer does not require trained analysts, and the calibrations do not require constant maintenance, making this an ideal way to monitor different fuels at service stations and more.
Figure 6. Examples of mobile fuel testing with the Metrohm DS2500 Petro Analyzer.
Learn more about the possibilities of petrochemical analysis with Metrohm DS2500 Analyzers in our free brochure.

NIRS as an ASTM compliant tool for QC

Method development

ASTM E1655: Standard Practices for Infrared Multivariate Quantitative Analysis

«These practices cover a guide for the multivariate calibration of infrared spectrometers used in determining the physical or chemical characteristics of materials. These practices are applicable to analyses conducted in the near infrared (NIR) spectral region (roughly 780 to 2500 nm) through the mid infrared (MIR) spectral region (roughly 4000 to 400 cm-1).»

Multivariate analysis of petroleum products

ASTM D8321: Standard Practice for Development and Validation of Multivariate Analyses for Use in Predicting Properties of Petroleum Products, Liquid Fuels, and Lubricants based on Spectroscopic Measurements

«This practice covers a guide for the multivariate calibration of infrared (IR) spectrophotometers and Raman spectrometers used in determining the physical, chemical, and performance properties of petroleum products, liquid fuels including biofuels, and lubricants. This practice is applicable to analyses conducted in the near infrared (NIR) spectral region (roughly 780 nm to 2500 nm) through the mid infrared (MIR) spectral region (roughly 4000 cm-1 to 40  cm-1).»

Method validation

ASTM D6122: Standard Practice for Validation of the Performance of Multivariate Online, At-Line, Field and Laboratory Infrared Spectrophotometer, and Raman Spectrometer Based Analyzer Systems

«This practice covers requirements for the validation of measurements made by laboratory, field, or process (online or at-line) infrared (near- or mid-infrared analyzers, or both), and Raman analyzers, used in the calculation of physical, chemical, or quality parameters (that is, properties) of liquid petroleum products and fuels.»

Results validation

ASTM D8340: Standard Practice for Performance-Based Qualification of Spectroscopic Analyzer Systems

«This practice covers requirements for establishing performance-based qualification of vibrational spectroscopic analyzer systems intended to be used to predict the test result of a material that would be produced by a Primary Test Method (PTM) if the same material is tested by the PTM.»

Typical NIRS applications and parameters for the petrochemical and refinery industry

Petrochemicals are subject to standardized test methods to determine their chemical, physical, and tribological properties. Laboratory testing is an indispensable part of both research and development and quality control in the production of petrochemicals. The following test parameters are typically important to measure in the petrochemical and refinery industry (Table 1).

Table 1. Examples for use of NIRS for selected petrochemical QC parameters.
Specific Gravity (API) Gravity meter ASTM D298











Boiling Point Distillation ASTM D2887
Cold Filter Plugging Point (CFPP) Standardized filter device ASTM D6371
Pour Point Pour Point analyzer ASTM D97
Cloud Point Cloud Point analyzer ASTM D2500
Flash Point Flash Point tester ASTM D93
Viscosity Viscometer ASTM D445
Color Colorimeter ASTM D1500
Density Densimeter ASTM D792
Fatty Acid Methyl Ester (FAME) FTIR ASTM D7806
Reid Vapor Pressure RVP analyzer ASTM D323
PIANO (Paraffins, Isoparaffins, Aromatics, Naphthenes, Olefins) Gas chromatograph ASTM D6729
Octane Number (RON/MON) CFR Engine ASTM D2699

ASTM D2700

Cetane Number CFR Engine ASTM D613
Diene value / MAV index Titration UOP 327-17
Parameter Conventional method ASTM method Relevant NIRS Application Notes

Future installments in this series

This article is a general overview of the use of NIR spectroscopy as the ideal QC tool for the petrochemical / refinery industry. Future installments will be dedicated to the most important applications and will include much more detailed information. Don’t miss our next blogs on the topics of:


For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.
From corn to ethanol: improving the fermentation process with NIRS

From corn to ethanol: improving the fermentation process with NIRS

The production of biofuels from renewable feedstock has grown immensely in the past several years. Bioethanol is one of the most interesting alternatives for fossil fuels, since it can be produced from (renewable) raw materials rich in sugars and starch.

Fermenting corn starch to produce ethanol for fuel is a complex biochemical process that requires monitoring of several parameters to ensure optimal production. Measuring these parameters via traditional laboratory techniques takes about an hour to complete and is a limiting step for increasing plant capacity and efficiency. Near-infrared spectroscopy (NIRS) can replace routine laboratory analysis, decreasing operating costs and increasing plant efficiency and capacity.

Learn more about this fast, non-destructive analysis technique in our different series of blog posts, including the benefits of using NIRS and some frequently asked questions.

Producing high quality ethanol as a fuel additive

Ethanol is an increasingly important component in the global fuel market, with countries looking to secure domestic fuel supplies and reduce their greenhouse gas emissions relative to fossil fuels. The United States and Brazil lead world bioethanol production, accounting for 83% of the supply.

According to the Renewable Fuels Association, approximately 26 billion gallons (nearly 100 billion liters) of ethanol were produced globally in 2020 [1], slightly reduced from a 2019 peak due to the global pandemic crushing demand for gasoline and ethanol as well. Demand for corn to transform into ethanol is still likely to rise as the United States increases adoption of E15 blends (15% ethanol in gasoline) [2]. Ethanol for export is also likely to increase in demand, with countries such as China implementing a E10 fuel standard for motor vehicles.

One of the primary ways to meet increasing product demand while maintaining price competitiveness is to increase plant capacity. However, the standard laboratory analytical workflow for monitoring the different parts of the fermentation process can be a limiting factor for growing a production site or improving its efficiency. Another consideration is the seasonal, and even regional variation of feedstock quality, requiring ethanol producers to closely monitor the fermentation process to ensure the same quality product is achieved.

A report from the National Renewable Energy Laboratory estimated that nearly 40% of the production cost of fuel ethanol from corn comes from labor, supplies, overhead, and variable operating costs [3]. Optimization of these costs, which include routine quality checks of the fermentation broth, regular maintenance of the fermenters and distillation towers, and triaging process upsets in a timely manner, leads to higher profitability of the ethanol production facility.

To maximize bioethanol production and profitability, laboratory limitations must be overcome. Near-infrared (NIR) spectroscopy is a proven economical, rapid, and operator friendly way to overcome common laboratory limitations. First, a bit of background information about the production of bioethanol is needed before jumping into how to optimize the process.

Ethanol process: wet vs. dry milling

There are two main production processes when it comes to creating ethanol from sugars and starches from starting materials such as corn: the wet milling process and the dry milling process (shown in Figure 1). Nearly all ethanol produced for fuel in the U.S. (the largest bioethanol manufacturer in the world) is made using the dry mill process [2].

Figure 1. Schematic representation of the dry mill ethanol process.

Grains are first ground into smaller, more homogenous particles in the dry milling process, which allows the husk or shell to be more easily penetrated. Water and enzymes are then added to create a slurry called a «mash». To facilitate the conversion of starches to sugars, the mash is heated to specific temperatures, then cooled before yeast is added. The yeast performs the work of creating ethanol from the converted sugars via the process of fermentation. However, the percentage of ethanol is still quite low, and therefore the solution must be distilled and dehydrated to obtain the concentration and purity necessary for fuel additives.

Wet milling differs from this process by first soaking the grains before grinding and separating out the various components. The starches are then converted to sugars which are used for the fermentation process, just as with dry milling.

If you want to know more about the fermentation process, read our blog post about optimization of beer brewing.

Lab analysis shortfalls

The lab serves many functions, but one of the key ones is to monitor the progress of the fermentation in each fermentation tank. This typically requires many different technologies, because several parameters must be checked to ensure that a fermentation is on track. Tight monitoring and control over the various sugars present (e.g., glucose, maltose, DP3, etc.) throughout the fermentation process is necessary to understand the breakdown pathway of the starch (glucose generation) present in the mash and optimize ethanol production. Understanding this pathway enables the proper dosage of enzymes and yeast to the mash in the slurry tanks (Figure 1) to accelerate breakdown. Therefore, optimizing the enzyme and yeast blend is crucial for this process. These are the highest consumable costs for ethanol production and significantly affect the rate of production and final yield of ethanol.

Some of the most common analytical instruments and their use cases are listed in Table 1.

Table 1. Typical instruments and parameters that are measured during fermentation of corn to ethanol.
Parameter Measurement technique Analysis time (min) incl. sample prep.
Dissolved solids (°Bx) Refractometer 3–5
pH pH meter 3–5
Solids (non-volatiles) Infrared balance 15–20
Ethanol HPLC 30–45

Sugar profile 
(DP2, DP3, DP4+, glucose, total sugar)

HPLC 30–45
Glycerol HPLC 30–45
Lactic acid Ion chromatography 30–45
Acetic acid Ion chromatography 30–45
Water content Karl Fischer titration 5–10

If all the properties in Table 1 are to be measured, it can easily take an hour using six different pieces of equipment. Factor in conditioning steps and reference scans to ensure proper calibration, and the time for a routine fermentation analysis increases. For a single corn fermentation, this can take upwards of 55 hours—one hour to perform the analysis and six hours between each measurement. However, increasing the number of concurrent fermentations to four or six means that measurements from the different tanks will begin to overlap.

Overlapping instrument demand combined with long analysis times results in a number of different challenges for bioethanol producers. First, if scheduled sampling times overlap, then sampling must either be delayed or samples must age while waiting for analysis. Second, the long analysis time means that data is no longer current, but minimally one hour or older by the time it has been communicated to the plant control center, which decreases the ability to deal with deviations. Neither of these situations is ideal for manufacturers—time is money, after all.

Long laboratory analysis times and infrequent measurements reduce the ability to perform interventions or to adjust other critical parameters (e.g., enzyme addition rate or process temperature). Additionally, such long wait times can impede the decision to end a fermentation early and begin anew if the batch is judged to be beyond recovery.

Faster measurements equal higher profits

The most obvious way to overcome measurement time challenges is to increase the number of tools in the lab and/or to add automation. However, this approach has costs in time; twice the sample preparation increases operating expenses and still fails to give high-speed feedback to the plant operations team.

A better way to overcome measurement time delays is to deploy near-infrared spectroscopy (NIRS), which can make all of the traditional laboratory measurements with one piece of equipment, at the same time, in less than five minutes.

Figure 2 displays the average ethanol concentration from HPLC measurements during several fermentations from one plant. The data shows apparent discontinuities in the first 12 hours, with spikes in glucose and dissolved solids. It is also apparent that the total solids measurement at 48 hours is erroneous. However, because the lab data requires so much time to collect, this spike is ignored instead of retested.

Figure 2. Key parameters measured for corn fermentation to ethanol as reported by the primary analysis methods listed in Table 1.

The NIRS alternative to traditional measurements shown in Figure 3 is of a single fermentation monitored in near real time. This high-speed analysis is possible because sample preparation is trivial for NIRS. Compared to the combination of HPLC and other analytical methods that consume about 60 minutes of operator time per sample, NIRS measures the same parameters and produces a quality result in about a minute. The ability to collect many NIR spectra in the early stages of the fermentation process provides a higher fidelity picture, enabling more timely interventions to maximize ethanol production.

The NIRS alternative to traditional measurements shown in Figure 3 is of a single fermentation monitored in near real time. This high-speed analysis is possible because sample preparation is trivial for NIRS. Compared to the combination of HPLC and other analytical methods that consume about 60 minutes of operator time per sample, NIRS measures the same parameters and produces a quality result in about a minute. The ability to collect many NIR spectra in the early stages of the fermentation process provides a higher fidelity picture, enabling more timely interventions to maximize ethanol production.

Figure 3. Corn fermentation to ethanol as measured by near-infrared spectroscopy.

The higher speed NIRS analysis can be used to increase total plant throughput by growing the number of batches and revenue, as shown in Table 2. With the traditional analysis, the fermentation is allowed to run 62–65 hours, depending on the final laboratory results (Figure 2).

With NIRS analysis, this fermentation is shown to be complete in around 56 hours (Figure 3). Reducing fermentation time by six hours expands the potential number of batches by 13 over the course of a year, representing a potential plant capacity increase of 10%.

Table 2. Comparison of the apparent fermentation time based on primary lab analyses vs NIRS analysis.
Traditional Lab Analysis NIRS Analysis

Total measurement time

12 hours

5 hours

Number of measurements



Fermentation end point

~62 hours

56 hours

Batch capacity

37,850 L

37,850 L

Batches per year



Download our free White Paper to learn more.

Near-infrared spectroscopic solutions for ethanol producers

Metrohm offers several NIRS solutions for ethanol producers to make analysis easier and optimize production. The DS2500 Solid Analyzer (Figure 4) is ideal for rapid laboratory analysis of several critical quality parameters in the fermentation process.

Download our free Application Note below to learn more about how Metrohm NIRS laboratory instruments perform quality control measurements for the fermentation process.

Figure 4. The Metrohm DS2500 Solid Analyzer.

Additionally, Metrohm also manufactures NIRS instruments for measurements directly in the process, eliminating the need for removing samples and transporting them to the laboratory. Measurements taken in this way are the most representative of actual process conditions and therefore provide the highest quality data to operators. Learn more here about our different ranges of NIRS process analyzers and accessories.

Data communication between the process analyzer and the control room allows a direct overview of current conditions without delays and offers the possibility of integrating warnings when readings are out of specification or informing operators when the fermentation process is deemed to be complete.

For more information about the usage of NIRS for process analysis in bioethanol production, download our free Application Note.


Near-infrared analysis decreases measurement time for in-process fermentation samples by approximately 90%, from one hour to five minutes. Faster measurements allow the fermentation process to be followed much more closely, saving operator time to reduce costs and to optimize process conditions and plant operations. Capacity improvements of 10% are possible by being able to stop the fermentations based on rapid determination of the different parameters in the fermenter with NIRS rather than by slower traditional laboratory methods.

NIR methodology can provide benefits across the ethanol plant beyond fermentation monitoring to measure the performance of other plant components such as a centrifuge or dryer, making it a valuable tool to improve operations across the facility.

For more information about utilizing NIRS analysis in the bioethanol process as well as the available precalibrations for various quality parameters, download our free White Paper.

Free White Paper

Improving the corn to ethanol fermentation process with near-infrared spectroscopy (NIRS)


[1]  Annual Fuel Ethanol Production U.S. and World Ethanol Production. Renewable Fuels Association: Washington, DC, 2021.

[2]  Essential Energy: 2021 Ethanol Industry Outlook. Renewable Fuels Association: Washington, DC, 2021.

[3]  Determining the Cost of Producing Ethanol from Corn Starch and Lignocellulosic Feedstocks. National Renewable Energy Laboratory (NREL): Golden, Colorado, USA, 2000.

Post written by Dr. Adam J. Hopkins (PM Spectroscopy at Metrohm USA, Riverview, FL) and Dr. Alyson Lanciki (Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland).

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 5

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 5

The history of polyurethanes

In 1937, the German chemist Dr. Otto Bayer (1902–1982) invented the versatile class of plastics we call polyurethanes. Polyurethanes are available in myriad forms—they are used in numerous products, from coatings and adhesives to shoe soles, mattresses, and foam insulation. Despite the variety in their characteristics, the underlying chemistry of these different forms is strikingly similar.

During World War II, the use of polyurethanes became popular as a replacement for rubber, which at the time was expensive and hard to obtain. Around the 1950s, polyurethanes began to be used in adhesives, elastomers, rigid foams, and flexible cushioning foams such as those used today.

Wallace Carothers, inventor of polyamide.
Dr. Otto Bayer was credited with inventing polyurethanes in 1937.

Nowadays, a life without polyurethane is difficult to imagine, as you can easily find it everywhere around you.

How is polyurethane created?


Polyurethanes are formed by reacting polyols (i.e., alcohols containing more than two reactive hydroxyl groups in each molecule) with di-isocyanates or polymeric isocyanates. Suitable catalysts and additives are used wherever necessary. Since both a variety of di-isocyanates and a wide range of polyols can be used to produce polyurethane, a large spectrum of polyurethane materials can be produced to meet the specific requirements for different applications. Polyurethanes can appear in a variety of forms including rigid foams, flexible foams, specialty adhesives, chemical-resistant coatings, sealants, and elastomers.

Figure 1. Molecular structures of isocyanates, polyols, and polyurethane.

Physical and chemical properties of polyurethanes

The properties of polyurethanes are highly dependent on their production process. When the polyol chain (Figure 1) is long and flexible, the final product will be soft and elastic. On the other hand, if the extent of cross-linking is very high, the final polyurethane product will be tough and rigid. The cross-linked structure of polyurethanes generally consists of three-dimensional networks which result in very high molecular weights. This structure also accounts for the thermosetting nature of the polymer since polyurethane typically does not soften or melt when exposed to heat.

One of the most popular forms of polyurethane is foam. This form is created by facilitating the production of carbon dioxide gas during the urethane polymerization process.

Typical applications of polyurethane

The primary application of polyurethane is in the production of foams (rigid and flexible). Other important applications and uses of polyurethane are listed below.


  • Low-density, flexible polyurethane foams are widely used in mattresses and automobile seats.
  • Bathroom and kitchen sponges are commonly made from polyurethane. It is also used in the manufacturing process of seat cushions and couches.
  • Polyurethane is also used to produce textiles used in some clothing and upholstery.
  • Due to its good insulating properties, polyurethane materials are commonly used in construction work.
  • Polyurethane moldings are also used in columns and door frames.
  • Flexible polyurethane is used in the manufacture of partially elastic straps and bands.
  • The low-density elastomers of polyurethane are widely used in the footwear industry.

In Table 1 a variety of polyurethane properties are compared to other conventional materials like rubber, metal, and plastic.

Table 1. Polyurethane in comparison with rubber, metal, and plastic.

PU vs. Rubber

PU vs. Metal

PU vs. Plastic

High abrasion resistance


High impact resistance

High cut and tear resistance

Noise reduction

Elastic memory

Superior load bearing

Abrasion resistance

Abrasion resistance

Thick section molding

Less expensive fabrication

Noise reduction


Corrosion resistance

Variable coefficient of friction

Oil resistance



Ozone resistance

Impact resistance

Thick section molding

Radiation resistance


Lower cost tooling

Broader hardness range

Easily moldable

Low temperature resistance

Castable nature


Cold flow resistance

Low pressure tooling


Radiation resistance

Near-infrared spectroscopy as a tool to assess the quality of polyurethanes

Near-infrared spectroscopy (NIRS) has been an established method for both fast and reliable quality control within the polyurethane industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.

There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.

In the remainder of this post, a short overview of polyurethane applications is presented, followed by available turnkey solutions for polyurethane analysis developed according the NIRS implementations guidelines of ASTM E1655-17.

Did you miss the first parts in this series? Find them here!

For more detailed information about NIRS as a secondary technique, read our previous blog posts on this subject.

Applications and parameters for polyurethanes with NIRS

When producing different types of polyurethanes, it is important to check certain parameters to guarantee the quality of the finished products. Typical parameters include hydroxyl number, acid number, moisture, and color in polyols as well as the NCO (isocyanates) content, (total) acid number, and moisture content in polyurethanes. The most relevant applications for NIRS analysis in polyurethane production are listed later in this article in in Table 2.

Where can NIRS be used in the polyurethane production process?

Figure 2 shows the individual steps from plastic producer via plastic compounder and plastic converter to plastic parts and foam producer.

Figure 2. Illustration of the production chain for polyurethanes.

Easy implementation of NIR spectroscopy for plastic producers

Metrohm has extensive expertise with analysis of polyamides and offers a turnkey solution in the form of the DS2500 Polyol Analyzer. This instrument is a ready-to-use solution for the determination of multiple quality parameters in polyols and polyurethanes. For the analysis of polyurethane pellets and parts, the Metrohm DS2500 Solid Analyzer is recommended.

Figure 3. Turnkey solution for polyurethane analysis with the Metrohm DS2500 Polyol Analyzer.

Learn more about the possibilities of polymer analysis with Metrohm DS2500 Analyzers in our free brochure.

Application example:

Pre-calibrations and starter model for the PU industry on the DS2500 Polyol Analyzer

The determination of the parameters listed below in Table 2 is a lengthy and challenging process with conventional laboratory methods. To measure them all, several different techniques are required which takes a significant amount of time, not only to analyze the sample, but also for the instrument management and upkeep.

Table 2. Primary method vs. NIRS for the determination of various quality parameters in PU samples.
Parameter Primary method Time to result (primary method) Relevant NIRS Application Notes NIRS benefits
Hydroxyl number in Polyols


90 min. preparation + 1 min. Viscometer





All three parameters are measured simultaneously within a minute, without sample preparation or the need of any chemical reagents
NCO (Isocyanate) content in PU HPLC 20 min. preparation + 20 min. HPLC
Moisture content

Karl Fischer Titration

25 min. preparation + 5 min. KF Titration


The NIRS prediction models created for polyols are based on a large collection of real product spectra and are developed in accordance with ASTM E1655-17 Standard practices for Infrared Multivariate Quantitative Analysis. For more detailed information on this topic, download the free white paper.

To learn more about pre-calibrations for polyols, download our brochure and visit our website.

One example of a dedicated ASTM standard referring to NIRS is ASTM D6342-12 Standard Practice for Polyurethane Raw Materials: Determining Hydroxyl Number of Polyols by Near Infrared (NIR) Spectroscopy. The following application example demonstrates that the DS2500 Polyol Analyzer operating in the visible and near-infrared spectral region (Vis-NIR) provides a cost-efficient and fast solution for the determination of the hydroxyl number in polyols and the NCO (isocyanate) content in polyurethanes. With no sample preparation or chemicals required, Vis-NIR spectroscopy allows analysis of all three quality parameters listed in Table 2 in less than a minute. The results are shown in Figure 4 and Figure 5.

Figure 4. Turnkey solution for determination of hydroxyl number in polyols using the Metrohm DS2500 Polyol Analyzer. A: Sampling and analysis of polyols. B: NIRS results compared to a primary laboratory method along with the Figures of Merit (FOM).
Figure 5. Turnkey solution for determination of NCO content (Isocyanates) in polyurethane using the Metrohm DS2500 Polyol Analyzer. A: Sampling and analysis of polyurethane. B: NIRS results compared to a primary laboratory method along with the Figures of Merit (FOM).

This application example demonstrates that NIR spectroscopy is excellently suited for the analysis of multiple parameters in polyols and polyurethanes in less than one minute without sample preparation or using any chemical reagents. Visit our website to learn more about our variety of analytical solutions for the polymer industry!

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.