3: The Vocabulary of Analytical Chemistry
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- 167741
If you leaf through an issue of the journal Analytical Chemistry, you will soon discover that the authors and readers share a common vocabulary of analytical terms. You are probably familiar with some of these terms, such as accuracy and precision, but other terms, such as analyte and matrix may be less familiar to you. In order to participate in the community of analytical chemists, you must first understand its vocabulary. The goal of this chapter, therefore, is to introduce you to some important analytical terms. Becoming comfortable with these terms will make the material in the chapters that follow easier to read and understand.
- 3.1: Analysis, Determination, and Measurement
- The first important distinction we will make is among the terms analysis, determination, and measurement. An analysis provides chemical or physical information about a sample. The component of interest in the sample is called the analyte, and the remainder of the sample is the matrix. In an analysis we determine the identity, concentration, or properties of an analyte. To make this determination we measure one or more of the analyte’s chemical or physical properties.
- 3.2: Techniques, Methods, Procedures, and Protocols
- 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.
- 3.3: Classifying Analytical Techniques
- Analyzing a sample generates a chemical or physical signal that is proportional to the amount of analyte in the sample. This signal may be anything we can measure, such as mass or absorbance. It is convenient to divide analytical techniques into two general classes depending on whether the signal is proportional to the mass or moles of analyte, or to the analyte’s concentration.
- 3.4: Selecting an Analytical Method
- A method is the application of a technique to a specific analyte in a specific matrix. We can develop an analytical method for determining the concentration of lead in drinking water using any of the techniques mentioned in the previous section. The requirements of the analysis determine the best method and consideration is given the following criteria: accuracy, precision, sensitivity, selectivity, robustness, ruggedness, scale of operation, analysis time, availability of equipment, and cost.
- 3.5: Developing the Procedure
- After selecting a method the next step is to develop a procedure that will accomplish the goals of our analysis. In developing the procedure attention is given to compensating for interferences, to selecting and calibrating equipment, to acquiring a representative sample, and to validating the method.
- 3.6: Protocols
- A protocol is a set of stringent written guidelines specifying an exact procedure that must be followed before an agency will accept the results of an analysis. A protocol contains explicit instructions regarding internal and external quality assurance and quality control (QA/QC) procedures. The goal of internal QA/QC is to ensure that a laboratory’s work is both accurate and precise. External QA/QC is a process in which an external agency certifies a laboratory.
- 3.7: The Importance of Analytical Methodology
- The importance of analytical methodology is evident if we examine environmental monitoring programs. The purpose of a monitoring program is to determine the present status of an environmental system, and to assess long term trends in the system’s health. These are broad and poorly defined goals. In many cases, an environmental monitoring program begins before the essential questions are known. This is not surprising since it is difficult to formulate questions in the absence of any results.
- 3.8: The Vocabulary of Analytical Chemistry (Exercises)
- These are homework exercises to accompany "Chapter 3: The Vocabulary of Analytical Chemistry" from Harvey's "Analytical Chemistry 2.0" Textmap.
- 3.9: The Vocabulary of Analytical Chemistry (Summary)
- This is a summary to accompany "Chapter 3: The Vocabulary of Analytical Chemistry" from Harvey's "Analytical Chemistry 2.0" Textmap.
Thumbnail: Colonies of fecal coliform bacteria from a water supply. Source: Susan Boyer. Photo courtesy of ARS–USDA (www.ars.usda.gov). Fecal coliform counts provide a general measure of the presence of pathogenic organisms in a water supply. For drinking water, the current maximum contaminant level (MCL) for total coliforms, including fecal coliforms is less than 1 colony/100 mL. Municipal water departments must regularly test the water supply and must take action if more than 5% of the samples in any month test positive for coliform bacteria.