Regulations
Francis Amore Henkel Corporation 2010 East Hennepin Minneapolis, Minnesota 55413
Good Analytical Practices
Since its inception, this column has been concerned with regulations as they affect the analytical chemist. A number of the reports, including the one in March (/), have addressed the question of licensing, registration, and certification of the analytical chemist. All of the regulations proposed which most directly affect the analytical chemist are aimed at assuring the reliability of analytical results that have become an integral part of regulatory and enforcement activities relating to human health and environmental health. Too often, most of these programs seem to have lost sight of their real purpose, i.e., how can the reliability of the data be controlled and evaluated. Too often, the focus is on the analysis, or on the facility, or on the method, when the concern should be with the quality of the final result. The fact that a chemist is licensed, a facility is certified, or a method is a "standard" method doesn't guarantee the quality or reliability of a reported number. However, if a reported number meets certain acceptable levels of accuracy and precision, then it is safe to say that the analysts did a good job, the facility was adequate for perform-
ing the work, and the method used was acceptable. Since there are inherent limitations in all measurements and therefore no absolutes in analytical results, it becomes apparent that what is needed is some indication of the reliability of the result, i.e., what is the precision and accuracy of the reported value and are these acceptable for the end use of the data. An approach which emphasizes quality assurance in laboratory operation as the best method for improving the reliability of analytical results is necessary. The concept is not new and should be common procedure in all laboratories performing analyses. Recently, Horwitz (2) has discussed the concept as an extension of the FDA Good Laboratory Practices relating to toxicological testing. The approach can be called Good Analytical Practices.
Also of concern are the tools of the measurement system. Reagents should be of the highest quality and checked for purity, strength, deterioration with time, and contamination. Class A volumetric glassware should be thoroughly cleaned and calibrated when necessary. Balances should be checked out with certified weights and records kept. All instruments should be calibrated with appropriate standards on a routine basis and operation logs on performance maintained. Acceptable inner and outer control limits should be established and control charts showing response and precision should be kept for each instrument. Quality assurance samples should be included along with the test sample at determined intervals such as every tenth sample. The protocol should have both an internal and external component.
Quality Assurance Protocol Any protocol for quality assurance must concern itself with both accuracy and precision. Cost and time must also be considered. In general, a laboratory should devote 10-20% of its effort to quality assurance.
Internal Components The internal steps include blind duplicates, blanks, spiked blanks, spiked samples, certified standards, synthetic samples, and secondary standard samples. Blanks are run to determine possible contamination; spiked blanks as an indication of general procedure performance. When using spiked samples to determine if potential matrix effects are influencing the final results and to check recoveries, it should be remembered that material added as a spike might not behave in the same manner as material incorporated by other mechanisms. Because of this possibility, precaution should be used in the interpretation of results from spiked samples. Samples should be spiked at levels consistent with the range of concentrations being measured in the sample. Certified samples such as those provided by NBS have reported values based on extensive analysis and are considered to be highly reliable based on the manner in which they were obtained (3). Unfortunately, only a few certified samples are available at this time for environmental studies.
Figure 1. Precision and accuracy through good analytical practices 0003-2700/79/A351-1105$01.00/0 © 1979 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 5 1 , NO. 11, SEPTEMBER 1979 • 1105 A
