An analytical method is essentially a list
of instructions for performing a laboratory test procedure. Analytical
methods development provides tools to answers the questions: “Is
it there”? And, if so, “How much of it is there”?
Thus, it involves both qualitative and quantitative analysis.
In practice, scientists may want to, say, apply a new repellent to
a crop to test its effectiveness against bird depredation. If the repellent
is ineffective, there may be multiple reasons. One important reason
may be that the repellent application process did not result in enough
of the repellent staying on the crop. To determine the concentration
of the repellent on the plants, one or more analytical methods may need
to be modified or developed.
How are Methods Developed?
Sometimes analytical methods are readily available, having been previously
developed by others. Some developed methods may need additional work
by NWRC chemists to make them applicable to Center research. Sometimes
methods must be developed from scratch.
For example, an NWRC chemist may want to develop a test for the repellent
methyl anthranilate (MA) on blueberries. First it must be determined
what MA is soluble in (often found in reference books such as the Merck
Index). The material to be tested must be in a soluble form for use
in analytical equipment. Then, if the sample is contaminated with other
materials (plant residues, soil, etc.) it must be purified or cleansed
as much as possible by running it through a procedure like liquid-liquid
extraction (or the newer solid-phase extraction) that removes materials
of no interest.
Next an analytical technique is selected, usually high-performance
liquid chromatography or gas chromatography, depending upon the thermic
stability of the molecule. All compounds have an identifiable pattern
of peaks on chromatographic paper. A peak or peaks associated with a
specific chemical or compound may be determined from the literature
or obtained from previous tests with technical grade samples of the
The detection system should not only aid in identifying the compound
present but also have sufficient sensitivity to quantify it. If a scientist
knows the purity of the manufacturer-supplied active ingredient, and
has developed “standards” from mixing a known amount of
the active ingredient in a known amount of solution, concentration of
the test material can be established.
Tetracycline, for instance, is often used as a biomarker, and NWRC scientists
have had to determine amounts of the compound in animal tissues. The
tissues are introduced into a liquid in which the tetracycline dissolves.
The resulting liquid is filtered and injected into the analytical instrument
to see how much tetracycline is present from the known amount of tissue.
Results are reported as micrograms of tetracycline per gram of tissue
(= concentration). Varying units of concentration are used depending
on how concentrated the active ingredient is in the tissue.
Once a method or procedure is developed it must be validated or tested
and documented. All NWRC methods are validated under EPA guidelines.
This work is performed by the NWRC Analytical Services group.
Types of Methods
Methods developed (or in development) by NWRC chemists include those
for analyzing the following:
methyl anthranilate on blueberries
acetaminophen in crabs
caffeine in rice paddy water
tetracycline in rat liver tissues and whole body
diphacinone in rat livers and whole body
brodifacoum in crab tissues
Goal and Objectives