John P. Coates

Infrared Spectroscopic Methods for the Study of Lubricant Oxidation Products

Data processing techniques have been developed for the manipulation and enhancement of spectroscopic data. They have been applied to the infrared spectra of degraded base oils and lubricants to provide information on oxidation processes and additive depletion. Samples have been acquired from oils that have been subjected to laboratory scale oxidation and from lubricants during standard engine tests. Results are evaluated in terms of chemical species that are lost and formed during oxidative degradation. Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

Vibrational Spectroscopy: Instrumentation for Infrared and Raman Spectroscopy∗

Abstract In reviewing the contents of this article, a decision had to be made regarding the presentation of the techniques for infiared and Raman spectroscopy. The problem lies in the complementary nature of these two techniques and the significant amount of overlap in both the instrumentation and the applications. It was decided that the audience would be served better if the two techniques were presented side-by-side within the same chapter. In this way, the similarities and dissimilarities can be assimilated conveniently, and for a person new to vibrational spectroscopy, it provides a more even-handed approach to these two powerful methods of analysis. However, having made the case for combining the techniques into a single chapter, the integrity of the techniques will be retained where necessary, and the individual techniques will be discussed separately, if appropriate. ∗Originally appeared in Analytical Instrumention Handbook, G. W. Ewing, ed., Marcel Dekker, Inc., 1997.

The Interpretation of Infrared Spectra: Published Reference Sources

INTRODUCTION Historically, infrared spectroscopy made its debut as an analytical tool during World War II. At that time it was used for quality control by several major chemical manufacturing companies. The instrumentation, which was essentially home-made, was adapted for the quantitative measurements of components in polymeric and petroleum products. In the 1950s, with the introduction of gas chromatographic instrumentation, infrared spectroscopy gradually fell out of favor as a quantitative tool. As a result, the emphasis switched to qualitative analysis. This was a natural role for infrared spectroscopy because of the significant amount of unique structural and chemical/physical information that is intrinsically available from the spectrum. The resultant increase in the use of infrared spectroscopy, as a qualitative tool, was aided by the influx of new, commercial instrumentation introduced during the 1950s - including lower priced, easy to use instruments for routine analysis. Much of the published wo...

Chasing ghosts?: the relevance of certain secondary or coincidental NIR correlations

For this installment of the Process Pages, John Coates has written an article dealing with a sticky analytical issue where some have claimed success using NIR spectroscopy. However, the use of multivariate mathematics with multi-channel spectroscopic data can produce results which seem to be successful based solely on the covariance of one analyte which can be detected, to a second analyte that cannot be detected. When this occurs, NIR can be used only when the covariance relationship always exists in precisely the same manner. It is important to look to the spectroscopic interpretation of the analyte signal of interest prior to making any rash cause and effect statements based on correlation mathematics alone. It is a good idea to look to the spectroscopy when evaluating the possibilities of using a particular spectroscopic technique for a particular analyte. A later installment of this series will address the specifics of the potential problems that may arise when mathematics alone is used to measure the success of spectroscopic methods.

Computer Based Infrared Search Systems

The infrared spectra of most chemical compounds are unique and it is this feature that enables a spectroscopist to identify an unknown substance from its spectrum. Traditionally this identification is attempted either by direct interpretation or from a possible match to a standard reference spectrum. A positive match is obviously more desirable but this is usually limited by the availability of a wide range of reference spectra and, if performed manually, it can be a very time consuming operation. The ability of a computer to handle a large number of data files and to be able to perform high speed repetitive operations make it an ideal candidate for spectral searches. In fact, this was considered to be one of the first main applications of the computer for analytical chemistry.

CONSIDERATIONS IN THE FLUORESCENCE DETECTION OF LOW LEVELS OF DISSOLVED SPECIES IN HPLC AND OTHER RELATED LIQUID FLOW TECHNIQUES

*Because of commercial issues and job-related changes, the original author of this article wishes to remain anonymous. He has, however, given approval for the publication and release of this article. The subject is both timely and appropriate in todays analytical marketplace.*Because of commercial issues and job-related changes, the original author of this article wishes to remain anonymous. He has, however, given approval for the publication and release of this article. The subject is both timely and appropriate in todays analytical marketplace.

Structural and chemical characterization of neopentyl polyol esters by infrared spectroscopy

Modern instrumental methods of analysis have been applied to the study of neopentyl-polyol-based synthetic ester lubricants. These provide information on the nature of the polyol(s), the component acyl groups and the composition in term of concentration and distribution of acyl groups. In most cases, the analyses are performed directly on the base oil or the lubricant without chemical modification. Infrared spectroscopy can play a major role in the analysis and, with suitable standards, it provides all of the important information for the chemical and structural characterization. Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

Application of Curve Fit and Deconvolution to Polymer Analysis

A great wealth of information about a material is found in its infrared spectrum. For many years infrared was used not just for identifying componds but also for obtaining semi-quantitative information about structural units. In more recent years other instrumental techniques, such as NMR, have been developed and have superseded infrared spectroscopy in the quantitative determination of structural information. Now, however, because of the availability of high signal-to-noise infrared spectrometers, and the computers associated with the spectrometers, structural information, which could not be accessed previously, can be extracted from the infrared spectrum. Techniques such as deconvolution and curve fit analysis provided by the computer, allow more structural information to be made visible in the infrared spectrum than was once thought possible. In the deconvolution process broad complex bands can be mathematically narrowed to yield an improvement in the observation of the overlapped component bands. The results obtained are often similar to those obtained from samples analyzed at low temperatures.

The Application of Data Enhancement Techniques to the Study of Hydrocarbon Oxidation Processes

Oxidative and thermal degradation of hydrocarbon oils are complex processes. While the fundamental chain reaction mechanisms are known, the actual chemistry of a formulation involving several additives still remains a gray area. An understanding of some of the additive interactions and their degradation pathways will ultimately lead to a more scientific approach to formulation optimization for a given application. Current methodology involves laboratory oxidation tests as a screening mechanism before the more expensive mechanical tests are used for the final lubricant evaluation. This is particularly the case for automotive and gas turbine lubricants. The chemistry linking the laboratory test and the mechanical tests for a given oil formulation are rarely considered.