Summary of Methods Used in the Study of Pesticide Biotransformation and Disposition - Pesticide Biotransformation and Disposition - page 5

and more effective pest management strategies. Although new techniques and instru-
ments continue to enter the commercial market, the basic analytical process has not
changed. One must:
l Define the research goal(s)
l Identify appropriate techniques and methods
l Develop a sampling scheme to obtain representative samples
l Isolate the compound(s) of interest
l Remove potential interfering components
l Quantify and evaluate the data in relation to the original research goals
Based on the data generated, many options are available. For example, was the
sampling scheme complete? Would further refinement of the analytical procedure be
required? Should other sample types be analyzed? Thus it is obvious that within these
general categories, particular methods vary considerably depending on the chemical
characteristics of the toxicant. This chapter is concerned with the sampling, isolation,
separation, and measurement of chemicals, which are needed to study the biotransfor-
mation and disposition of pesticides. It is intended to give the reader a brief summary
of some of the methods used in the elucidation of the disposition and metabolism of
pesticides. Because an exhaustive treatment of this topic would require several volumes,
the topics will be covered in such a way as to give the reader an overview and a “nod-
ding acquaintanceship” with the topic. The reader is directed to the cited references for
a more thorough treatment of individual topics.
ANALYTICAL METHODS FOR PESTICIDES AND PESTICIDE
METABOLITES
Elucidation of the often complex mechanisms and pathways involved in pesticide
biotransformation requires well-thought-out and well-controlled experiments. One
of the cornerstones of these studies is good analytical chemistry methods that will
produce robust and reliable data on the parent compound, metabolites, and (poten-
tially) changes in gene and protein expression. This starts with an appropriate sampling
technique, including not just the collection of the sample but an appropriate handling
and storage process as well. The samples are then cleaned up (if necessary) and enriched
so that they may be identified. There are a wide variety of techniques available; how-
ever, the use of mass spectrometry (MS) coupled with either gas chromatography (GC)
or liquid chromatography (LC) is among the most prevalent. In this section we discuss
these methodologies as well as tools used for toxicokinetics.
Sampling
Even with the most sophisticated analytical equipment available, the resulting data
are only as representative as the samples from which the results are derived. The vast