Summary of Methods Used in the Study of Pesticide Biotransformation and Disposition - Pesticide Biotransformation and Disposition - page 7

via a stainless steel funnel with a steep-angled surface and which is covered with a spe-
cial nonwetting material. The cone is equipped with an apparatus to separate the urine
and feces into two different collection containers. The cages are also equipped with
special food and water containers to prevent spillage into the sample collection area.
For more on the collection of urine from laboratory animals, the reader is referred to
Kurien et al. (2004) or Hayes (2008) . Bile, on the other hand, can be collected via a
cannula inserted into the bile duct of an anesthetized animal. However, not allowing
the bile salts to circulate can lead to changes in the physiology of the animal.
Tissue
The collection of tissue can range from collecting small biopsies of muscle or adipose
tissue to harvesting entire organs from necropsied animals. If one is investigating the
biotransformation of pesticides in plants, it may include the collection of plant material
such as leaves or stems. In all of these cases, the procedure is relatively uncomplicated
and the biggest concern will tend to be the mass of sample available for collection, as
this will affect the sensitivity of the analysis.
Other Methods
Although this is not an exhaustive list, there are a few other sampling methodologies
that are worthy of note. The first is the use of microdialysis. The principle of dialy-
sis is that compounds will partition through a semipermeable membrane, driven by
the concentration gradient across the membrane. Although there are various designs,
this sampling method generally uses a small concentric probe of dialysis tubing with a
membrane at the tip. Perfusate can be cycled through the probe at a constant flow rate
and collected in a vial ( Plock and Kloft, 2005 ). The advantages of this type of sampling
are that samples can be collected at the site of interest and the samples are free of pro-
tein that can confound analysis. In addition, samples can be collected over a period of
time to determine toxicokinetic profiles without concern for blood loss in the animal.
Some of the drawbacks of this technique include the potential for tissue trauma at the
site of the probe insertion as well as the potential for bacterial contamination. In addi-
tion, the size of the sample is relatively small and therefore the analytical technique
chosen has to have sufficient sensitivity to detect the analytes at very low concentra-
tions. One such apparatus uses a microdialysis pump that directly injects into a high-
performance liquid chromatography (HPLC) system with a mass spectrometer ( Davies,
2000 ). In addition to its use in animals, the microdialysis technique has been used to
determine pesticide residue concentrations in plants ( Zhou et al., 2009 ).
Another technique that shows some promise in this area is the use of solid-phase
microextraction (SPME). This solventless technique was first introduced in the early
1990s but has found much of its use in the flavor and fragrance industry as well as for