Imaging, Chemometrics and New Developments in Sensor Technologies
Committee E13 on Molecular Spectroscopy and Chromatography
by Jerome (Jerry) Workman, Jr.
ASTM Committee E13 on Molecular Spectroscopy and Chromatography has traditionally fulfilled a mission to facilitate the advancement of the field of molecular spectroscopy involving absorption, luminescence, scattering, or polarization of radiant energy; nuclear magnetic resonance; and the advancement of the field of chromatography. This main committee promotes the exchange of information, sponsors meetings and symposia for the presentation of papers, standardizes terminology, and coordinates and formulates scientific practices relative to methods of analysis. The work of this committee is coordinated with other committees and organizations having mutual interests.
Committee E13 has been meeting on a regular basis since its inception in 1950. Its members meet twice a year, generally in March at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy (Pittcon), and October/November at either the Eastern Analytical Symposium (EAS) or the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) meeting. The committee currently has jurisdiction over 30 active standards published in Volume 03.06 of the Annual Book of ASTM Standards.
A renewed interest in the development of level zero and level one tests to include the latest trends in instrumentation technology is an area of growing interest among the 150-plus members of E13. A level one test is a simple series of measurements designed to provide quantitative data on various aspects of spectrophotometer performance and information on which to base the diagnosis of problems. A level zero test is a routine check of spectrophotometer performance, which can be done in a few minutes, designed to visually detect significant changes in instrument performance and provide a database to determine instrument performance over time.
Molecular Spectroscopic Optical Imaging
A new subcommittee, E13.10 on Molecular Spectroscopic Optical Imaging, is organized with the purpose of developing standard practices and terminology for spatial and spectral imaging and mapping techniques. Chemical and medical imaging is a combination of molecular spectroscopy and imaging technologies. Data sets generated by imaging systems are quite large, are multivariate in nature, and require significant data processing and computational power. Image analysis is so powerful as a technique because it exploits the ability of humans to interpret spatial information rapidly and effectively. The combination of chemical and physical-optical information combined with spatial-structural information yields much richer information content than non-imaging methods.
Initial subcommittee meetings have discussed the use of mid-infrared (MIR), near infrared (NIR), Raman, and fluorescence (FL) imaging practices. Task groups are being formed to look at best practices for macro- and microspectroscopic imaging, standards for spatial and spectral resolution, NIR microspectroscopy, NIR macroscopic imaging, and general mapping techniques and practices. For mid-infrared such topics as frequency calibration, intensity calibration, linearity testing, terminology, flat fielding, pixel biasing and associated topics are under discussion. Microbeam techniques are another topic of interest to this newly formed group.
Subcommittee E13.11 on Chemometrics is concerned with defining chemometric methods for batch processing and manufacturing as well as terminology for this rapidly advancing field. Chemometrics can generally be described as the application of mathematical and statistical methods to (1) improve chemical measurement processes, and (2) extract more useful information from chemical and physical measurement data. This group has recently discussed such topics as chemometric methods for pharmaceutical applications, and the development of standard libraries for the testing of data processing and preprocessing algorithms. The main task of this group has been to codify chemometric methods for manufacturing and process control applications where it is critical that the analytical method pass the criteria demanded by strict scientific scrutiny. Calibration of infrared and near infrared spectrometers is one of the most popular uses of chemometrics in both academic and industrial circles.
The challenge to the chemometric subcommittee is that many analytical chemists in academia and industry do not take advantage of the power offered in using multivariate chemometric methods. Chemometrics is often considered to be overly complicated. The mathematical methods can be misinterpreted and misused or are considered esoteric and not relevant. Due to the wide latitude of interpretation of these mathematical techniques readily available in many modern software packages, problems can easily arise in the implementation and maintenance of these methods for routine measurements. There is a lack of official practices and methods associated with chemometrics.
However through the diligent efforts of E13.11, an excellent document has been generated and updated that thoroughly describes many of the confusing aspects of chemometricsE 1655, Practices for Infrared, Multivariate, Quantitative Analyses. This standard includes a guide for the multivariate calibration of infrared (IR) spectrometers used in determining the physical or chemical characteristics of materials. The practice applies to the NIR spectral region (roughly 780 to 2500 nanometres) through the MIR spectral region (roughly 4000 to 400 cm-1). In addition, the practice also includes procedures for collecting and treating data for developing IR calibrations. Definitions for terms and calibration techniques are described. Criteria for validating the performance of a calibration model are also described.
This practice provides the first comprehensive official working document for the application of chemometric multivariate analysis techniques to NIR, IR, and other spectrometers. Technical discussions are included for selecting the calibration set; determination of concentrations or properties, or both, for calibration samples; and the collection of IR and NIR spectra. In addition, the topics of calculating the mathematical model, validating the mathematical model, and applying the finished model for analysis of unknowns is described; the technical issues for routine analysis and monitoring, and calibration transfer are included within the practice. The mathematics of multilinear regression (MLR), principal components regression (PCR), and partial least squares (PLS) are delineated; with a discussion of the estimation of parameter values from spectra also included.
Ultraviolet and Visible Spectroscopy
Subcommittee E13.01 on UV-Vis Spectroscopy is involved with such activities as practices and test methods for calibration and characterization of spectrophotometers. In addition, issues such as stray radiant power ratio of spectrophotometers is being addressed for NIR, UV-Vis, and the specifics of modern diode-array instrumentation. This subcommittee has the task of updating specific traditional practices and methods into suitable standards for the most advanced modern instruments. A task group of E13.01 is in detailed discussions regarding the use of spectroML, i.e., generalized analytical markup language (GAML) and extensible markup language (XML) data formatting and related issues. Although file and communications standards are critical to on-line and manufacturing-based applications of spectroscopic data, there is currently no accepted standard for data formatting.
E13.03 is the subcommittee working directly with the various aspects of infrared spectroscopy. The current activity of this working group includes new practices and standards for spectral searching, a new infrared method to determine the condition of used oil, a guide to Fourier-transform infrared spectroscopy, qualification of optical instruments for molecular spectroscopy, and a practice for spectral searching algorithms. In addition, older practices and methods are in the process of being updated to include imaging, chemometrics, and new array-based technologies. As an example, the Infrared Search Algorithm Task Group is exploring the database requirements, methods, and the recent advances in computer-based search mathematics in order to create a new method for spectral searching that will include the traditional wisdom of spectroscopists that understand the importance of accurate techniques for spectral interpretation, classification, and identification.
Subcommittee E13.19 on Chromatography has the task of updating and maintaining important chromatographic practices, methods and terminology standards. Various task groups update chromatographic terms and are initiating expanded methods for LC-MS, micro-LC and micro-GC, as well as capillary electrophoresis.
The E13.08 Raman subcommittee is leading discussions and work to create standards and materials for an intensity standard, a resolution standard, and a Raman shift standard. The molecular spectroscopic optical imaging subcommittee is reviewing the requirements for spatial and spectral standards for Raman imaging applications.
Recent advances in the measurement fields described within this article have presented E13 with exciting opportunities and challenges in the development and modernization of standards. The rapid expansion of knowledge and technology in imaging, computer assisted methods, and data analysis are in the forefront of these changes. E13 activities provide an active venue for advancing the measurement techniques essential to research, manufacturing, and quality issues for multiple products and industries. Participation in E13 not only provides state-of-the-art information to members, but also helps in the proliferation of sound scientific and technological practices on a global scale. //
Copyright 2002, ASTM