Techniques, Methods, Procedures, and Protocols
Suppose you are asked to develop a way to determine the concentration of lead in drinking water. How would you approach this problem? To answer this question it helps to distinguish among four levels of analytical methodology: techniques, meth- ods, procedures, and protocols.
A technique is any chemical or physical principle that can be used to study an analyte. Many techniques have been used to determine lead levels.2 For example, in graphite furnace atomic absorption spectroscopy lead is atomized, and the ability of the free atoms to absorb light is measured; thus, both a chemical principle (atom- ization) and a physical principle (absorption of light) are used in this technique.
A method is the application of a technique for the determination of a specific analyte in a specific matrix. As shown in Figure 3.2, the graphite furnace atomic ab- sorption spectroscopic method for determining lead levels in water is different from that for the determination of lead in soil or blood. Choosing a method for deter- mining lead in water depends on how the information is to be used and the estab- lished design criteria (Figure 3.3). For some analytical problems the best method might use graphite furnace atomic absorption spectroscopy, whereas other prob- lems might be more easily solved by using another technique, such as anodic strip- ping voltammetry or potentiometry with a lead ion-selective electrode.
A procedure is a set of written directions detailing how to apply a method to a particular sample, including information on proper sampling, handling of interfer- ents, and validating results. A method does not necessarily lead to a single proce- dure, as different analysts or agencies will adapt the method to their specific needs. As shown in Figure 3.2, the American Public Health Agency and the American Soci- ety for Testing Materials publish separate procedures for the determination of lead levels in water.
Finally, a protocol is a set of stringent written guidelines detailing the proce- dure that must be followed if the agency specifying the protocol is to accept the re- sults of the analysis. Protocols are commonly encountered when analytical chem- istry is used to support or define public policy. For purposes of determining lead levels in water under the Safe Drinking Water Act, labs follow a protocol specified by the Environmental Protection Agency.
There is an obvious order to these four facets of analytical methodology. Ide- ally, a protocol uses a previously validated procedure. Before developing and vali- dating 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. We begin by considering a useful way to classify analyti- cal techniques.