Summary of Methods Used in the Study of Pesticide Biotransformation and Disposition - Pesticide Biotransformation and Disposition - page 6

majority of errors in analytical measurements are introduced during the sample col-
lection, preservation, and storage. Therefore a great deal of effort should go into
the planning of this phase of the study and care must be taken to ensure that the
resulting data meet the objectives of the study. Often special attention to sampling
procedures is necessary. Ultimately, the initial hypothesis and goals of the study will
determine what will be the most appropriate sampling schemes and analytical meth-
ods. In its simplest form, the goal in developing a sampling scheme is to come up
with a representative sample, or representative samples. What this means is a sample that
truly reflects the composition of the matrix to be analyzed within the context of the
study aims.
In the context of this discussion, the samples of interest will tend to be biologi-
cal. They may include whole blood, plasma, urine, bile/feces, cell culture media, saliva,
adipose and organ tissue, or plant material. Each of these sample media has unique
characteristics that could affect the choice of method, but there are a few constants that
should be kept in mind. First, and foremost, any use of human tissue samples should
have all appropriate informed consent and IRB approvals in place at the outset. With
that said, there are some common considerations regardless of the matrix. Sample col-
lection apparatus should be clean and of an appropriate material. For instance, highly
hydrophobic compounds could adhere to polyethylene or silicone parts in a collec-
tion syringe and reduce the amount of compound available for analysis. Sample storage
containers should likewise follow this rule. In general, glass containers with Teflon-
lined lids are the most common. If the compound is photolabile, then the containers
should be amber or otherwise protected from light. If the samples are not going to be
analyzed immediately, then they should be stored at  20 to  80°C.
Blood
In human volunteers, this type of collection is relatively straightforward; in rodents,
however, it is more problematic. Blood or plasma can be collected from laboratory ani-
mals through a variety of mechanisms. In smaller rodents it is especially important that
the frequency of collection is not such that it significantly alters the total blood volume
of the organism. In rats, 100- to 200-µl blood samples can be collected from the tail
vein. In addition, a more complex method is to anesthetize the animal and insert a
cannula into the external jugular vein. The orbital sinus in mice can be used to collect
blood but only under terminal anesthesia, whereas in rabbits, the terminal ear vein may
be used as a collection site without anesthesia ( Hayes, 2008 ).
Urine and Bile
As with blood, collection of urine or fecal samples is not overly problematic with
human volunteers. In rodents, urine and fecal samples can be collected by placing the
animal in a metabolism cage. In this type of apparatus, the urine and feces are collected