General Steps in a Chemical Analysis

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Introduction

The analytical process often begins with a question that is not phrased in terms of a chemical analysis. The question could be "Does lead in petrol enter our food supply?" or "Is this water safe to drink?" or "Does emission testing of automobiles reduce air pollution?" A scientist translates such questions into the need for particular measurements. An analytical chemist then must choose or invent a procedure to carry out those measurements,
When the analysis is complete, the analyst must translate the results into terms that can be understood by others ­ preferably by the general public. A most important feature of any results is its limitations. What is the statistical uncertainty in reported results? If you took samples in a different manner, would you obtain the same results? Is a tiny amount (a trace) of analyte found in a sample really there or is it contamination? Once all interested parties understand the results and their limitations, then they can draw conclusions and reach decisions.

The Process

Formulating the question	1.	Translate general questions into specific questions amenable to being answered through chemical measurements.
Selecting analytical procedures	2.	Search the chemical literature to find appropriate procedures or, if necessary, develop original procedures to make the required measurements.
Sampling	3.	Obtain a representative bulk sample from the lot.
	4.	Extract from the bulk sample a homogeneous laboratory sample.
Sample preparation	5.	Convert the laboratory sample into a form suitable for analysis, which usually means dissolving the sample. Samples with a low concentration of analyte may need to be concentrated prior to analysis.
	6.	Remove or mask species that interfere with the chemical analysis.
Analysis	7.	Measure the concentration of analyte in several aliquots. The purpose of replicate measurements (repeated measurements) is to assess the variability (uncertainty) in the analysis and to guard against a gross error in the analysis of a single aliquot. The uncertainty of a measurement is as important as the measurement itself, because it tells us how reliable a measurement is. If necessary, use different analytical methods on similar samples to make sure that each method gives the same result and that the choice of analytical method is not biasing the result. You may also wish to construct and analyse several different bulk samples to see what variations arise from your sampling procedure.
Reporting and interpretation	8.	Deliver a clearly written, complete report of your results, highlighting any special limitations that you attach to them. Your report might be written to be read only by a specialist (such as your instructor), or it might be written for a general audience (such as your mother). Be sure the report is appropriate for its intended audience.
Drawing conclusions	9.	Once a report is written, the analyst might or might not be further involved in what is done with the information, such as modifying the raw material supply for a factory or creating new laws to regulate food additives. The more clearly a report is written, the less likely it is to be misinterpreted by those who use it. The analyst should at least have the responsibility to ensure that conclusions drawn from his or her data are consistent with the data.