|KOK, ANDRE DE|
Submitted to: Trends in Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2008
Publication Date: 1/1/2009
Citation: Lehotay, S.J., Mastovska, K., Amirav, A., Fialkov, A.B., Alon, T., Martos, P.A., Kok, A., Fernandez-Alba, A.R. 2009. Identification and confirmation of chemical residues by chromatography-mass spectrometry and other techniques. Trends in Analytical Chemistry. 27(11):1070-1090.
Interpretive Summary: Numerous applications require analytical chemists to determine what chemicals are in the sample and how much of the detected chemicals are there. This is the basis for qualitative and quantitative analysis in analytical chemistry, and one of the fundamental questions is how well does the analyst know that the signal analyzed is actually the chemical of interest. Science does not allow 100% certainty in the result, so analytical chemists have devised criteria, particularly in chemical residue applications for regulatory enforcement, that help the analyst determine if the chemical is “identified” or not. In the absence of scientific certaintly, though, this topic is a matter of scientific debate. In this paper, we add our voices to the debate by reminding the analytical community to conduct multiple analyses using independent methods, and not to rely on any single set of results even if the most sophisticated techniques are used. This minimizes the chances of mistakes and false accusations made in the regulatory arena.
Technical Abstract: A quantitative answer cannot exist in an analysis without a qualitative component to give enough confidence that the result meets the analytical needs for the analysis (i.e. the result relates to the analyte and not something else). Just as a quantitative method must typically undergo an empirical validation process to demonstrate that it is fit for purpose, qualitative methods should also empirically demonstrate suitability for the needs of the analysis; however, thorough qualitative method validation requires analysis of a great number of samples (possibly more than can be reasonably done), which is commonly avoided due to the time and effort involved. Instead, mass spectrometry (MS) is generally assumed to be the gold standard for qualitative methods, and its results are typically unquestioned. For example, a system of MS identification points (2002/657/EC) was developed by European regulators of veterinary drug residues in food animals, in which a different number of identification points are given in MS analyses depending on the general degree of selectivity of the MS technique used. This well-defined approach gives a definite answer for decision-makers, and for that reason it has attained growing popularity, but the point system is not scientific. The reality is that each situation requires information gathering and careful deductive thinking on the part of the analyst to make MS identifications. Rather than devising arbitrary requirements that need to be met by an unthinking analyst, we wish to remind the analytical community that confirmation can only be made from two or more independent analyses in agreement, preferably using orthogonally selective (independent) chemical mechanisms. In this article, we discuss the proper use of terminology, demonstrate how MS identifications can fail, discuss the identification power of various MS techniques, and re-assert the value of basic confirmation practices, qualitative method validation, informational checklists, routine quality control procedures, and blind proficiency test analyses.