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Methods Development

   
 

 

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 chemical.

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


 

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