NIR spectroscopy in the petrochemical and refinery industry: The ASTM compliant tool for QC and product screening – Part 5
History of ASTM International
The American Society for Testing and Materials (ASTM) is an organization that currently provides over 12,500 international standards. Its roots date back to 1898, when ASTM was formed by a group of scientists and engineers to address the frequent rail breaks affecting the fast-growing railroad industry. The group developed a standard for the steel used to fabricate rails.
Originally, this organization was called the «American Society for Testing Materials» (1902) and was changed to the «American Society for Testing and Materials» in 1961. In 2001, ASTM officially changed its name to «ASTM International» and added the tagline «Standards Worldwide». This tagline was modified in 2014 to «Helping our world work better». Now, aside from the US, ASTM International also has offices in Belgium, Canada, China, and Peru.
ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants
Formed in 1904, ASTM Committee D02 currently meets twice per year for five days of technical meetings, attended by approximately 1000 members (out of around 2500). D02 has jurisdiction over 814 standards with a prominent role in all aspects relating to the standardization of petroleum products and lubricants, which are published in the Annual Book of ASTM Standards (Volumes 05.01 through 05.06).
Near-infrared spectroscopy—an ASTM compliant tool to assess the quality of petrochemical products
Near-infrared spectroscopy (NIRS) has been an established method for 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 NIRS as an alternative technology.
Many companies are not aware that now there are many ASTM standards about how to implement NIR spectroscopy as an alternative to conventional methods. Several NIRS-related ASTM guidelines are shown in Figure 1.
Figure 1. Overview of NIRS-related ASTM guidelines.
«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).»
«This practice covers the use of near-infrared (NIR) spectroscopy for the qualitative analysis of liquids and solids. The practice is written under the assumption that most NIR qualitative analyses will be performed with instruments designed specifically for this purpose and equipped with computerized data handling algorithms.»
«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.»
These requirements include the following topics:
- Analyzer calibration
- Correlation of NIRS vs. lab method (treated and untreated samples)
- Probationary validation
- General & Continual validation
«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).»
The main purpose for this standard is to establish the validity of test results during calibration.
«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.»
Furthermore, it includes the prescriptive requirements regarding multivariate models, including Multi Linear Regression (MLR), Partial Least Square (PLS), Principal Component Regression (PCR), Cross validation, and Outlier statistics, as well as instrument considerations.
Regarding the required accuracy of the NIRS method the expected agreement and user requirements is that the Standard Error of Prediction for the NIRS value should be equal to or smaller than the laboratory method reproducibility.
ASTM D8340 compliance with the NIRS DS2500 Petro Analyzer and Vision Air
Temperature stability, section 5.4:
There are prescriptive requirements included in this norm regarding temperature stability of the NIRS Analyzer. Section 5.4 requires sample temperature to be carefully controlled in the analyzer system hardware or that effects of temperature change be compensated in the modeling or software. Metrohm’s solution to this issue for the NIRS DS2500 Petro Analyzer is shown in Figure 2.
Figure 2. Temperature stability for the NIRS DS2500 Petro Analyzer.
Analyzer wavelength accuracy and precision, section 6.3:
Section 6.3 requires that the analyzer shall include a means of demonstrating that it is operating within the vendor’s speciﬁcation. Therefore, the analyzer shall incorporate instrument performance tests to demonstrate that it is operating within historically expected limits. Furthermore, the analyzer shall have a means of validating wavelength/frequency precision and accuracy. Also, the wavelength precision must be sufficient to allow spectra to be collected and used in creating a multivariate model that meets or exceeds user’s speciﬁcations. The wavelength precision of the analyzer used for calibration and the analyzer-to-analyzer wavelength accuracy and reproducibility must be sufficient to allow analyzers to be validated by Practice D6122. Metrohm’s solution to this is the Vision Air software shown in Figure 3.
Figure 3. Analyzer wavelength accuracy and precision for ASTM D8340 section 6.3 (click to enlarge image).
Vendor created global multivariate model, section 8.2.2:
The multivariate model can be that of a standardized test method, a user/vendor-created global multivariate model, or a user-created site-speciﬁc multivariate model. A global multivariate model is one developed by use of samples and data that may represent materials produced at multiple facilities or locations. Some locations may start with a global model and add site-speciﬁc sample to it. Metrohm offers several pre-calibrations for the NIRS DS2500 Petro Analyzer, listed in Figure 4.
Figure 4. Available NIRS pre-calibrations for the petrochemical industry.
Outlier statistics, sections 9.3, 9.4, and 9.5:
The requirements of outlier handling are described in these sections. Identiﬁcation and handling of outliers is important to the success of meeting this performance-based practice. It is permissible for the identiﬁcation and handling of outliers to be performed by the same or separate software used for generating predictions from spectra. For analysis of a sample for the purposes of determining property values, the software shall indicate whether the spectrum is identiﬁed as an outlier, based on the criteria set by the user. The sample analysis may indicate that expected performance is not reached for a sample identiﬁed as an outlier.
Vision Air is Metrohm’s universal software for Vis-NIR spectroscopy. Vision Air accounts for the unique needs of each type of instrument user. It offers specific interfaces optimized for the most common tasks – simplifying routine measurement, method development, outlier handling, and both data and instrument management. Vision Air is also compatible with third-party software like Unscrambler (Figure 5).
Figure 5. Vision Air—Metrohm’s universal software for lab Vis-NIR spectroscopy.
In the petrochemical industry, typical requirements from management are usually that quality control should be quick, operating costs should be low, feedback should be fast, and operation should be safe.
Typical requirements from the user are that the analysis should be accurate and precise, and the instrumentation should be easy to use, fast, and safe.
NIR spectroscopy is compliant with all of these requirements, and as shown in this blog series, the technology is supported by several ASTM guidelines for method development, method validation, and results validation.
By utilizing NIRS in the petrochemical industry, manufacturers not only improve the efficiency of screening and quality control of petrochemical products, but also fully adhere to internationally accepted standards.
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We offer NIRS for lab, NIRS for process, as well as Raman solutions