Analytical Standardization and Calibration

Briefly explain the differences between calibrating an analytical balance and calibrating a pH meter and what happens if the measured standard does not give the correct result. 

The ability to make analytical measurements depends intimately on the availability of well-defined standards and calibrants. Many measurements of analytes in seawater (such as dissolved organic carbon and dissolved organic nitrogen) cannot be compared among laboratories because of the lack of appropriate reference materials and blanks for instrument calibration and testing. Intercomparison exercises are critical (NRC, 1993, p. 75). 

J.S. Shenk and M.O. Westerhaus, New standardization and calibration procedures for NIRS analytical systems. Crop Sci. 31, 1694-1696 (1991). 

An offline analytical HPLC method with small injection volumes can be used to confirm the composition of cuts collected from a preparative run. Ideally, an analytical HPLC method provides an acceptable separation of the mixture components, displays peaks that can be assigned to known components, and gives a detector response that is a linear function of analyte concentration. Using isolated standards and calibrating the analytical detector for the concentration of each component is a good way to know the mass of each component eluting from a chromatography column, when such standards are available. 

The control of analytical variables, which includes analytical methodology, standardization and calibration procedures, documentation of analytical protocols and procedures, and the monitoring of critical equipment and materials. 

The quality of the calibrators and the calibration procedure used are major factors in determining the reliability of the analytical values obtained with a procedure. To appreciate the problems in standardization and calibration, knowledge of the overall structure of an accuracy-based measurement system is necessary. Uriano and Cali and Tietz have defined a hierarchy of analytical methods and reference materials that shows the relationship between reference materials and analytical methods of different quality. Figure 19-7 illustrates how "field methods are related to "reference methods by secondary reference materials and how reference methods are related to definitive methods by primary reference materials. ... 

Sampling is one of the most important operations in a chemical analysis. Chemical analyses use only a small fraction of the available sample. The fractions of the sandy and loam soil samples shown in the photo that are collected for analyses must be representative of the bulk materials. Knowing how much sample to collect and how to further subdivide the collected sample to obtain a laboratory sample is vital in the analytical process. Sampling, standardization, and calibration are the focal points of this chapter. All three steps require a knowledge of statistics. 

Gravimetric methods do not require a calibration or standardization step (as do all other analytical procedures except coulometry) because the results are calculated directly from the experimental data and atomic masses. Thus, when only one or two samples are to be analyzed, a gravimetric procedure may be the method of choice because it requires less time and effort than a procedure that requires preparation of standards and calibration. 

Chapter 3 Using Spreadsheets in Analytical Chemistry 54 Chapter 4 Calculations Used in Analytical Chemistry 71 Chapter 5 Errors in Chemical Analyses 90 Chapter 6 Random Errors in Chemical Analysis 105 Chapter 7 Statistical Data Treatment and Evaluation 142 Chapter 8 Sampling, Standardization, and Calibration 175... 

On the other hand, a number of factors hamper the development and validation of analytical methodologies alternative to the biological bioassays. A serious problem is that accurate and readily available calibration standards are required for each of the various toxins. The lack of pure analytical standards and reference materials has always been—and still is—the major drawback both in shellfish toxin research and monitoring. Moreover, only limited progress has been achieved in the synthesis of these compounds. 

The separation of dairy proteins by CE has been generally carried out by CZE and has been exhaustively covered in several review papers, - - thus Table 30.8 only presents the key methodologies that offer the reader an overview of their most distinctive features. Basically, dairy protein analysis has been performed in whole milk for the simultaneous determination of caseins and whey proteins, or in fractions isolated from milk after casein precipitation. The first approach being used when the quantitative determination of the major proteins is required for the calculation of casein/whey protein ratios or for authentication purposes where an analysis of the whole protein profile is required. In both cases, accurate quantitative data must be derived. However, few studies have addressed the analysis of both groups of proteins in a single run by presenting quantitative data based on calibration curves constructed with analytical standards and good recovery of all proteins from milk samples. 

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