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Benefits of NIR spectroscopy: Part 2

Benefits of NIR spectroscopy: Part 2

This blog post is part of the series “NIR spectroscopy: helping you save time and money”. 

Infrared spectroscopy and near infrared spectroscopy – is there a difference?

This is the second installment in our series about NIR spectroscopy. In this post, you will learn the background of NIR spectroscopy on a higher level and determine why this technique might be more suitable than infrared spectroscopy for your analytical challenges in the laboratory and in the process.

Spectroscopy… what is that?

A short yet accurate definition of spectroscopy is «the interaction of light with matter». We all know that light certainly influences matter, especially after spending a long day outside, unprotected. We experience a sunburn as a result if we are exposed to the sun for too long.

A characteristic of light is its wavelength, which is inversely correlated to its energy. Therefore, the smaller the wavelength, the more energy there is. The electromagnetic spectrum is shown in Figure 1. Here you can see that the NIR region is nestled in between the visible region (at higher energy) and the infrared region (at lower energy).

Figure 1. The electromagnetic spectrum. (Click to enlarge.)

Light from both the infrared (IR) and near-infrared (NIR) region (800–2500nm) of the electromagnetic spectrum induces vibrations in certain parts of molecules (known as functional groups). Thus IR and NIR belong to the group of vibrational spectroscopies. In Figure 2, several functional groups and molecules which are active in the NIR region are shown.

    Figure 2. Major analytical bands and relative peak positions for prominent near-infrared absorptions. Most chemical and biological products exhibit unique absorptions that can be used for qualitative and quantitative analysis. (Click to enlarge.)

    The difference in the vibrations induced by IR or NIR spectroscopy is due to the higher energy of NIR wavelengths compared to those in the IR region.

    Vibrations in the infrared region are classified as fundamental—meaning a transition from the ground state to the first excited state. On the other hand, vibrations in the near infrared region are either combination bands (excitation of two vibrations combined) or overtones. Overtones are considered vibrations from the ground state to a level of excitation above the first state (see Figure 3). These combination bands and overtones have a lower probability of occurring than fundamental vibrations, and consequently the intensity of peaks in the NIR range is lower than peaks in the IR region.

    Figure 3. Schematic representation of the processes occurring with fundamental vibrations and with overtones. (Click to enlarge.)

    This can be better understood with an analogy about climbing stairs. Most people climb one step at a time, but sometimes you see people in a hurry taking two or three stairs at once. This is similar to IR and NIR: one step (IR – fundamental vibrations) is much more common compared to the act of climbing two or more stairs at a time (NIR – overtones). Vibrations in the NIR region are of a lower probability than IR vibrations and therefore have a lower intensity.

    Theory is fine, but what does this mean in practice?

    The advantages of NIR over IR derived from the theoretical outline above are:

    1. Lower intensity of bands with NIR, therefore less detector saturation.

    For solids, pure samples can be used as-is in a vial suitable for NIR analysis. With IR analysis, you either need to create a KBr pellet or carefully administer the solid sample to the Attenuated Total Reflectance (ATR) window, not to mention cleaning everything thoroughly afterwards.

    For liquids, NIR spectra should be measured in disposable 4 mm (or 8 mm) diameter vials, which are easy to fill, even in the case of viscous substances. IR analysis requires utilization of very short pathlengths (<0.5 mm) which require either costly quartz cuvettes or flow cells, neither of which are easy to fill.

    2. Higher energy light with NIR, therefore deeper sample penetration.

    This means NIR provides information about the bulk sample and not just surface characteristics, as with infrared spectroscopy.

    However, these are not the only advantages of NIR over IR. There are even more application related benefits:

    3. NIR can be used for quantification and for identification.

    Infrared spectroscopy is often used for detecting the presence of certain functional groups in a molecule (identification only). In fact, quantification is one of the strong points of utilizing NIR spectroscopy (see below).

    4. NIR is versatile.

    NIR spectroscopy can be used for the quantification of chemical substances (e.g. moisture, API content), determination of chemical parameters (e.g. hydroxyl value, total acid number) or physical parameters (e.g. density, viscosity, relative viscosity and intrinsic viscosity). You can click on these links to download free application notes for each example.

    5. NIR also works with fiber optics.

    This means you can easily transfer a method from the laboratory directly into a process environment using an analyzer with a long, low-dispersion fiber optic cable and a rugged probe. Fiber optic cables are not possible to use with IR due to physical limitations.

    NIR ≠ IR

    In summary, NIR is a different technique than IR, although both are types of vibrational spectroscopy. NIR has many advantages over IR regarding speed (easier handling, no sample preparation needed), providing information about the bulk material as well as its versatility. NIR allows for the quantification of different kinds of chemical and physical parameters and can also be implemented in a process environment.

    In the next installment of this series, we will focus on the process of implementing a NIR spectrometer in your laboratory workflow, using a specific example.

    For more information

    about NIRS solutions provided by Metrohm, visit our website!

    We offer NIRS analyzers suitable for laboratory work as well as for harsh industrial process conditions.

    Post written by Dr. Dave van Staveren, Head of Competence Center Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.

    Determining the total sulfite in food and beverages: faster and easier than ever

    Determining the total sulfite in food and beverages: faster and easier than ever

    The chances are good that if you’re reading this, you are an analytical chemist or somehow connected to the food science sector. Maybe you have had the lucky experience of measuring sulfite (SO32-) before in the laboratory. I certainly have, and the adventure regarding tedious sample preparation and proper measurement of such a finicky analyte still haunts me today, years later.

    Why sulfite?

    Sulfite is a preservative added to a vast range of foods and beverages to prevent browning or oxidation. Some individuals are sensitive to sulfite additives and may experience a range of allergic reactions. Therefore, both the U.S. Food and Drug Administration (FDA) and European Union (EU) laws require that the presence of sulfites be declared on food labels when the concentration exceeds 10 mg/L.

    To put this into perspective, an Olympic size swimming pool can hold about 2,500,000 liters, meaning anything beyond 25 kilograms (the average mass of one young child!) would need to be reported.

    So, which foods contain sulfite?

    Many foods and beverages contain sulfite – whether added to prolong the freshness, or occurring naturally as a byproduct from processes like fermentation. Typically, the first things that come to mind are wine, beer, or dried fruit snacks. However, many pickled and otherwise preserved items such as sauerkraut, canned fruits and vegetables, and even frozen foods contain significant levels of sulfites. Processed meats, several condiments, and some prepared doughs are also high on the list of offenders, so beware at your next picnic!

    If you think you may be sensitive to sulfites, don’t forget to check the nutrition facts, and try to avoid such foodstuffs.

    How is sulfite usually measured?

    Several analytical methods exist to measure sulfite in food and beverages, however they suffer from repeatability issues, and can be quite cumbersome to perform.

    Traditionally, the optimized Monier-Williams (OMW) AOAC Official Method 990.28 was used for quantification of sulfite in most foodstuffs, but the method detection limit now lies at the regulatory labeling threshold. Automated discrete analysis methods have been reported for sulfite analysis, but they are limited by their strong dependence on sample matrix type. Therefore these methods are less than ideal for laboratories where sulfite analysis is required for a wide variety of food and beverage products.

    Methods based on ion chromatography (IC) with conductivity detection exhibit a lack of selectivity combined with an extended analysis time due to separation challenges. A newer method developed by AOAC (Method 990.31) focuses on the use of ion-exclusion chromatography followed by electrochemical (amperometric) detection of samples.

    Another issue arises concerning the sensitivity of the detector. After a few injections, fouling from contaminants rapidly decreases the electrode sensitivity. Frequent reconditioning of the working electrode is necessary due to a rising background and baseline noise, and can be accomplished in a couple of ways. Manual polishing and utilizing pulsed amperometric detection (PAD) pulse sequences are the most common choices to recondition the surface of the working electrode, while other methods opt for disposable electrodes to avoid this step altogether.

    What has improved?

    Metrohm has filed a patent for an innovative, fast, and accurate ion chromatographic (IC) method based on direct current (DC) mode electrochemical detection. It works with the implementation of a unique working electrode conditioning function (patent pending) in the newest version of chromatographic software (MagIC Net 3.3) offered by Metrohm. A great diversity of food and beverage products were analyzed with sulfite recovery values near 100% in all cases. Using a single, robust chromatographic method, any sample can be treated identically, saving time and making laboratory work much easier.

    Sample of garlic analyzed for sulfite content (spiked: red, unspiked: black). Recovery was calculated at 100%.
    (Click to enlarge)

    No matter what type of sample (solid, liquid), the preparation steps are nearly identical, and much simpler to perform than ever before. Additionally, the retention time of sulfite in the method does not shift. This saves even more time for analysts as they do not have to reprocess data. Since the electrode is automatically reconditioned after each analysis, results are both reliable and reproducible. Waste from disposable electrodes is reduced, as well as costs incurred by the materials and excess working hours which would generally be spent performing other manual steps. This is truly a win-win situation for food analysis!

    Benefits to QC laboratories and beyond

    In real terms, this improved method allows for up to 10x the throughput of samples compared to conventional methods. Previously, the contract laboratories involved in this study could measure 5 samples, with 2 analysts per 8-hour shift (15 samples per 24 hours, if you like). With our patent-pending technique, at 10 minutes per sample, including fully automatic regeneration of the electrode surface, this allows for up to 144 samples to be analyzed every day.

    Whether you work in the food and beverage industry, wastewater analysis, or in daily analytical laboratory work, you can appreciate the numerous benefits this method offers. Robustness, reproducibility, time savings, cost savings, and a simpler procedure for sample preparation across the board – are you interested? With our expertise in ion chromatography as well as electrochemistry, among other techniques, Metrohm is able to offer such cutting edge methods for the most challenging applications.

    Want to learn more?

    Download our free Application Note:

    Sulfite determination in food and beverages applying amperometric detection

    Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland.

    Special thanks are given to Miguel Espinosa, Product Manager Ion Chromatography, at Metrohm Hispania (Madrid, Spain) for his assistance in providing the laboratory data for the study.

    Avoiding the most common mistakes in pH measurement

    Avoiding the most common mistakes in pH measurement

    If you’re reading this, then I’m sure you have already performed at least one pH measurement in your lifetime, since it is one of the most important parameters in analytical chemistry. I remember my first contact with a potentiometric pH meter and a pH electrode – and I can still remember how I felt back then.

    I was young and completely unsure how I should handle the instrument and the electrode. Was I doing everything correctly? Consequently I had many questions about the best practices.

    Today, I am much more confident! Therefore, I would love to share with you some of the most common uncertainties and mistakes I see during my daily work when potentiometric pH measurements are performed. By the end of this article, I am certain that you will agree with me: pH measurement can be just as easy as it looks. I will cover the following topics (click to go directly to each topic):

    Is this the correct electrode for your application?

    Troubleshooting already starts before you put the sensor into your sample solution. A wide variety of electrodes are available on the market, and it can be quite difficult to determine which electrode is the best for your application. Many different diaphragm types as well as glass membrane materials exist:

    We’ve prepared a flyer for you to help find the perfect electrode for your application. Additionally, we have provided valuable information about maintenance and storage. You can download the flyer in several languages: English, German, French, or Spanish.

    What’s most important when preparing the electrode for calibration or measurement?

    Before starting your measurement, check the electrode for cracks or contaminations. Open the plug to ensure that the electrolyte can flow out (otherwise you may observe unstable results), and check the level of the electrolyte.

    The electrolyte should always be filled up to the opening in order to ensure an outflow from the hydrostatic pressure. If the level of the sample is higher than the level of electrolyte within the sensor, then sample will enter the reference system of your electrode. This causes the reference potential to shift, and results are no longer reproducible.

    Make sure that you insert your sensor deep enough into the sample. At least the glass membrane and the diaphragm need to be covered, as shown in this example.

    Calibration: When is it necessary, and what must I consider?

    Calibrations must be performed on a regular basis. Depending on the number of measurements and the sample matrix, I recommend calibrating at least weekly. If used often, or if the sample matrix is contaminating the sensor, then you should calibrate daily or even more frequently. Of course you should always calibrate your sensor if you have received a new one, after maintenance, or after a longer storage period.

    For calibration, consider the following points:

    • Always use fresh (not expired) buffers – the calibration can only be as good as the buffers used!
    • Perform at least a 2-point calibration.
    • Your sample pH should be within the calibration buffer pH value.
    • Always measure the temperature, as the pH value is temperature-dependent.
    • Most manufacturers already include buffer table templates with their instruments. Make sure that you select the correct one.

    How should you store the pH electrode?

    The correct storage of the pH electrode can increase its lifetime significantly. Never store the pH electrode dry! The glass membrane builds up a hydration layer, which is necessary for proper pH measurement. If you store the electrode dry, this hydration layer will be destroyed. Even though the layer can be recovered by conditioning the sensor in deionized water, the sensor will become slower.

    For electrodes filled with potassium chloride (c(KCl) = 3 mol/L) as reference electrolyte, we have developed a dedicated storage solution which keeps the glass membrane in top quality without impairing the performance of the diaphragm.

    The figure above shows how quickly the sensor responds when placed in a sample after a storage period. You can clearly see that storing the sensor in the dedicated solution leads to a much faster response time in comparison to storage in c(KCl) = 3 mol/L. This means even more productivity and less waiting.

    All electrodes which are filled with another reference electrolyte than c(KCl) = 3 mol/L are stored in their reference electrolyte.

    How should the pH electrode be cleaned?

    Between the measurements, the electrode must be rinsed well with deionized water. If the sample is sticky or contains proteins, use a suitable solvent to remove the contamination. From time to time, it is important to give the electrode a «special treat» and clean it with the pHit Kit, shown below. This set includes everything that is necessary to gently and efficiently clean the electrode.

    Very important: Never wipe the sensor off with a tissue! Similar to rubbing the surface of a balloon, you will charge the surface of the glass membrane. The built-up electrostatic energy will influence your measurement, which will get significantly longer. Additionally, you can scratch the sensitive glass membrane surface, thus destroying it.

    To stir or not to stir?

    Depending on the electrode type you are using, it is recommended to always stir constantly, at the same speed, during analysis. The following graph illustrates why:

    The upper curve shows the measurement with an electrode having a fixed ground-joint diaphragm, and the lower curve utilized a very common electrode with a ceramic pin diaphragm. 

    Not only does the top electrode show less signal noise, the signal remains nearly unchanged once the stirrer is switched off. However, there is a significant signal drop for the ceramic pin diaphragm (bottom). Therefore, the stirring speed should be identical for all buffers and samples to minimize such effects. 

    Is my electrode still ok to use?

    To get an idea about whether your electrode is still ok to use or not, it is generally enough to check the slope and the pH(0) after calibration. The slope should be between 95–103%, whereas the pH(0) should lie between pH 6.8–7.2. Further information can be gained if a pH electrode test is performed, which is implemented in some of Metrohm’s instruments, or a test according to application bulletin AB-188.

    If the electrode does not meet the specifications, clean it according to the instructions and perform the test again. If the sensor still does not pass, a replacement is inevitable.

    Check out our webinars:

    «Basic of pH measurements» or «Troubleshooting of pH measurement

    You can also download our whitepaper WP-003 «pH measurement: Six technical tips»  for free: 

    Post written by Dr. Sabrina Gschwind, Jr. PM Titration (Sensors) at Metrohm International Headquarters, Herisau, Switzerland.

    Benefits of NIR spectroscopy: Part 2

    Benefits of NIR spectroscopy: Part 1

    This blog post is part of the series “NIR spectroscopy: helping you save time and money”. 

    People who are unfamiliar with near-infrared (NIR) spectroscopy frequently ask the question: “Why should I need to know more about this technique, and how can I benefit from it?”.

    In this first installment of in this series of posts, we focus on the main advantages of NIRS over conventional wet chemical analysis methods and will provide examples of the types of parameters that can be measured with NIR spectroscopy.

    Solid vs. liquid samples

    In order to understand the benefits of NIRS, a good starting point is to understand how the NIR spectrum is measured. NIR spectroscopy can be used to analyze different types of samples. However, different instrumentation is required depending on the sample type. Several measurement methods are available for samples ranging from clear liquids to opaque pastes and powders. Choosing the right measurement method, sampling module, and accessories is the most important step to developing robust NIR methods. Below, the different methods are shown for various sample types (diffuse reflection, diffuse transmission, transflection, and transmission).

    Diffuse reflection: Cream, paste, granulates, coarse & fine powders

    NIR light penetrates into and interacts with the sample, and the unabsorbed NIR energy reflects back to the detector. This method is most suitable to measure solid samples without sample preparation.

    Diffuse transmission: Tablets and capsules

    As with diffuse reflection, the NIR light penetrates into and interacts with the sample. This light is scattered throughout the sample, due to interaction with the particles. The unabsorbed NIR light is transmitted through the sample prior to reaching the detector. This method is most suitable to measure solid dosage forms without sample preparation.

    Transflection: Liquids and gels

    This measurement method is a combination between transmission and reflection. A reflector is placed behind the sample, used to reflect the unabsorbed NIR light back to the detector. This method is most suitable to measure liquid samples.

    Transmission: Liquids

    In this situation, the sample is placed between the NIR light source and the detector. NIR light is transmitted through the sample, and any unabsorbed NIR energy continues to the detector. This method is most suitable to measure clear liquid solutions or suspensions.

    Solid sample measurement

    Solid samples (such as powders) must be placed on the window as shown here, secured within an appropriate container or vial. The instrument lid needs to be closed prior to starting the analysis so external light does not affect the results.

    The NIR radiation comes from below, and is partially reflected by the sample to the detector, which is also located below the sample vessel plane. After 45 seconds, the measurement is completed and a result is displayed. As this reflected light contains all the relevant sample information, this measurement technique is called diffuse reflection.

    Liquid sample measurement

    As the image illustrates, for liquid analyses via NIRS, a vial or cuvette must be placed in the drawer of the instrument. After pressing start, the drawer closes automatically and a result is obtained after 45 seconds.

    In this case, the NIR radiation travels through the solution before reaching the detector. This measurement technique is known as transmission.

    Advantages of NIRS

    The procedure for obtaining the NIR spectrum already indicates two main advantages of NIRS: simplicity regarding sample measurement and speed. These and other advantages of NIR are listed here:

    • Fast technique with results in less than 1 minute.

    • No sample preparation required – solids and liquids can be used in pure form.

    • 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.

    How to quantify with NIRS

    NIRS is a secondary technique, which means a prediction model will need to be created first. You can compare this, for example, to HPLC. If you want to identify or quantify a substance with that technique, you would need to prepare standard solutions of the substance and measure them to create a calibration curve.

    This is similar with NIRS: first you need to measure a number of spectra with known concentrations or known parameter values gathered from a primary method such as titration. A prediction model is then created out of these spectra using chemometric software, e.g. the Metrohm Vision software. We will explain in more detail how prediction models are created in another installment of this series.

      Application versatility in all industries

      NIRS is a versatile technique and can be used for various applications, both for chemical and physical parameters. You can find many different application examples for NIR in the Metrohm Application Finder. Here, we have listed representative examples for some industry segments.

      • Polymers: Density of Polyethylene (PE); Melt Flow Rate; Intrinsic Viscosity

      • Chemical: Hydroxyl number of polyols

      • Petrochemical: Research Octane Number (RON) of gasoline; cetane index for diesel

      • Oils and Lubricants: Total Acid Number (TAN)

      • Pharma: Water content of lyophilized products; content uniformity in tablets

      • Personal care: Moisture content and active ingredients in creams

      Overall, near-infrared spectroscopy is a robust alternative technique for the determination of both chemical and physical parameters in solids and liquids. It is a fast method which can also be successfully implemented for routine analysis by staff without any laboratory education. 

      In the next installment we will answer another frequently asked question: “Is near-infrared the same as infrared spectroscopy?”.

      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 Dr. Dave van Staveren, Head of Competence Center Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.

      When do I have to exchange the filtration membrane with Inline Ultrafiltration?

      When do I have to exchange the filtration membrane with Inline Ultrafiltration?

      Inline sample preparation is a powerful tool to make your ion chromatography analysis more efficient. Inline Ultrafiltration is an easy add-on that works for many samples. Use it for any type of sample which contains particles, like surface water, groundwater, or wastewater.

      Inline Ultrafiltration by Metrohm

      Ion chromatography is equipped with Inline Ultrafiltration in many branches to save time and money, e.g.:

      • Water
      • Environmental
      • Pharmaceutical
      • Food/beverage
      • Chemical
      This combination increases filtration effectiveness and sample throughput. Consumables such as syringe filters are not necessary, and the workload for sample preparation in the laboratory is significantly reduced.

      How often is optimal?

      Customers often ask me about how often the membrane in an Ultrafiltration cell needs to be exchanged. There is no strict limit to the number of injections per membrane filter. This number strongly depends on the level of contamination of the samples.

      The optimal point in time can be easily determined using our intelligent software. MagIC Net allows you to automatically integrate a check standard measurement after a certain number of samples. When the membrane filter begins to clog, the check standard data will deviate from its accepted value. MagIC Net automatically evaluates this value, and a warning message will inform you that it is time to check the system and to exchange the membrane.

      Add this feature to any MagIC Net method. Define the monitoring period for the desired result.

      In any case that the limit value is exceeded, a warning message will pop-up in the software. The data file is highlighted in red in the database, and the respective result is also displayed in red.

      Ultimate flexibility for your needs

      Monitoring the check standard is useful for several analytical methods. In this example, I explained how to use it to automatically control the performance of the Inline Ultrafiltration. Of course, the MagIC Net software has many more options for flexible methods with feedback. Contact your Metrohm representative if you want to learn more.

      For more information

      about inline sample preparation techniques for ion chromatography, visit our website!

      Metrohm Inline Sample Preparation (MISP)

      Post written by Dr. Katinka Ruth, Senior Application Specialist Ion Chromatography at Metrohm International Headquarters, Herisau, Switzerland.
      Why your titration results aren’t reproducible: The main error sources in manual titration

      Why your titration results aren’t reproducible: The main error sources in manual titration

      In the practical course in Analytical Chemistry during my first semester at university, I had to titrate a lot. Thinking back on it, I remember carefully dosing titrant with the glass buret, the cumbersome process of refilling the buret, and the constant suspicion that I hadn’t correctly chosen the endpoint.

      Everyone in class kept getting different results—but we were never quite sure why. At the time, I wasn’t as experienced as I am now. Today, after 10 years of experience in titration, I’ve learned that the results of manual titration depend quite a lot on the person carrying it out. Here are the top error sources in manual titration and how you can avoid them.  

      Choosing the right indicator I’m sure you’ve learned at some point that the pH value of the titration endpoint depends on the acid dissociation constant (Ka) of the acid and base that are used. If a strong base is titrated by a strong acid, the pH value at the endpoint is around 7. The titration of a strong base with a weak acid shifts the endpoint towards the alkaline range. The titration of a strong acid with a weak base will result in an endpoint in the acidic range. This explains why several different indicators are used in acid-base titrations. But which is the right one to choose?
      The chart above shows some of the most frequently used pH indicators. You can probably imagine that you won’t get correct results when the pH of your endpoint is around 7, but you use crystal violet or methyl orange as the indicator. Luckily, most standards and SOPs specify an indicator. Follow the instructions, and you’re on the safe side!

      Endpoint recognition is subjective

      The problems really start when you try to recognize the endpoint. Have you ever thought about the nuances of the color change?

      Above, you see five stages of an acid-base titration of c(HCl) = 1 mol/L with c(NaOH) = 1 mol/L. The only difference between each image and its predecessor is one additional drop of titrant. Where would you choose the endpoint in this case?

      Is the endpoint reached in picture 1, where only a faint pink is visible? Or is it reached in picture 3 where the color becomes more intense? Or even in picture 5, at which point the pink color is most vibrant? Between picture 1 and picture 5, just four drops of titrant were added. With the pharmaceutical definition of a drop as a volume of 50 µL, this corresponds to 200 µL of titrant or about 7.3 mg of hydrochloric acid—an enormous error.

      Reading the buret volume

      Do you remember how to correctly read the buret? You have to stand on a footstool and make sure that you read the meniscus value horizontally. Do you know why?

      The volume reading depends upon the angle from which you view the buret. In the case shown here, the readings vary up to 0.2 mL (200 µL) from the actual value, depending on the reading angle. The more your line of sight deviates from the horizontal, the more inaccurate the reading—and the result. You can assume an average error of 200 µL. This is a lot for a titration, as I showed in the previous example!

      Improving objectivity and accuracy

      How can you eliminate these errors? The easiest one to overcome is the reading error. The solution for this is to use an electronic buret. When using an electronic buret, all you need to do is fill it with the titrant and then you press a button. The device automatically measures the volume and gives you a digital readout. Using an electronic buret ensures already a high level of objectivity for your results.

      It also improves the accuracy of your results. I don’t have to tell you how important accuracy is in analytical chemistry, but I’ll give an example. Imagine you determined the purity of gold at 90%, but in reality, it’s 99% pure. You would lose a lot of money when selling your gold under this pretense!

      Earlier, I showed that visual endpoint recognition using a color indicator can result in errors of up to 200 µL. An inaccurate buret reading can lead to an additional 200 µL error. While using an electronic buret doesn’t help you achieve a more objective endpoint recognition, it does reduce the minimum volume addition per drop: it’s no longer 50 µL, but can be as small as 0.25 µL depending on the cylinder volume you use. This substantially lowers the error resulting from endpoint recognition. The following minimum volume additions are common:

      The next step: Automated titration

      If you want to overcome all sources of error described in this post, you’ll have to switch to automated titration, or autotitration. In this case, you will use a sensor to measure pH change in the sample and a mathematical algorithm to detect the endpoint—an indicator isn’t required anymore. Additionally you have the same precision as with the electronic buret.

      Want to learn more?

      Download our free White Paper:

      Manual vs. Automated Titration: Benefits and Advantages to Switching

      Post written by Iris Kalkman, Product Specialist Titration at Metrohm International Headquarters, Herisau, Switzerland.