Suppose you are asked to develop an analytical method to determine the concentration of lead in drinking water. How would you approach this problem? To provide a structure for answering this question let’s draw a distinction among four levels of analytical methodology: techniques, methods, procedures, and protocols.1
- A technique is any chemical or physical principle we can use to study an analyte. There are many techniques for determining the concentration of lead in drinking water.2 In graphite furnace atomic absorption spectroscopy (GFAAS), for example, we first convert aqueous lead ions into a free atom state—a process we call atomization. We then measure the amount of light absorbed by the free atoms. Thus, GFAAS uses both a chemical principle (atomization) and a physical principle (absorption of light).
- A method is the application of a technique for a specific analyte in a specific matrix. As shown in Figure 3.2, the GFAAS method for determining lead in water is different from that for lead in soil or blood.
- A procedure is a set of written directions telling us how to apply a method to a particular sample, including information on obtaining samples, handling interferents, and validating results. A method may have several procedures as each analyst or agency adapts it to a specific need. As shown in Figure 3.2, the American Public Health Agency and the American Society for Testing Materials publish separate procedures for determining the concentration of lead in water.
- A protocol is a set of stringent guidelines specifying a procedure that must be followed if an agency is to accept the results. Protocols are common when the result of an analysis supports or defines public policy. When determining the concentration of lead in water under the Safe Drinking Water Act, for example, labs must use a protocol specified by the Environmental Protection Agency.
There is an obvious order to these four levels of analytical methodology. Ideally, a protocol uses a previously validated procedure. Before developing and validating a procedure, a method of analysis must be selected. This requires, in turn, an initial screening of available techniques to determine those that have the potential for monitoring the analyte.
Figure 3.2 Chart showing the hierarchical relationship among a technique, methods using that technique, and procedures and protocols for one method. The abbreviations are APHA: American Public Health Association, ASTM: American Society for Testing Materials, EPA: Environmental Protection Agency.