might spill or otherwise present the possibility for contamination. The glassware or other containers used in sampling and shipping should be subjected to any cleaning procedures recommended in the analytical method.
Careful record keeping in the field is also important. Pertinent information such as temperature, humidity, possible interfering compounds, sampling location, etc. should be documented. Special care should be taken in sample labelling and in preparation of paperwork accompanying the samples so that confusion in the laboratory is avoided.
Field blanks are used to estimate contamination which may occur immediately before and after sampling, during shipment, or while awaiting measurement in the laboratory. The nature and number of blanks taken will depend on the method and sampling situation; therefore, field sampling personnel must attempt to determine what sources of contamination are possible in the specific situation at hand. The field blank strategy must then be designed accordingly. Where possible, a written sample protocol should be developed before actual sampling begins.[1][2][3][4] The protocol should contain a description of the environment being sampled; the assumptions made in derivation of the model of that environment; when, where, and how the sampling will be done; and how many samples will be taken. Samplers should be identified by batch or lot number of sampling media.
4. QUALITY ASSURANCE IN MEASUREMENT
Certain quality control checks should be performed with each sample set[5][2] to further support the reported results on actual field samples. The exact number and nature of these checks depend on the specific method and circumstances under consideration and should be thought of as an integral part of the method itself (i.e., a measurement should not be considered completed without the quality control checks also being completed). Each analyst must take an independent responsibility for assuring that the analytical quality control system works. This can be accomplished by using known spiked samples which closely simulate field samples with regard to concentration and interferences. Since the analyst is most familiar with the methods being used and should know what range of recoveries to expect, problems with the system can be detected early. We will attempt to recommend specific quality control checks to be performed with the methods in NMAM; however, our recommendations cannot be expected to cover all situations. The user of these methods should consider adding additional quality control checks as appropriate.
- Methods
First, and perhaps most important in the area of quality control, a laboratory must have adequate measurement procedures. These methods should be written so that there is no doubt in the analyst's mind of the exact steps which must be performed and so that future references to the work can be as exact as possible. The methods used should be evaluated, where possible (either by the laboratory itself or by some other organization), to verify that the methods perform satisfactorily. Factors which could be evaluated include the recovery of the analyte of interest from both spiked samples and
- ↑ Taylor, J. K. Quality Assurance of Chemical Measurements, Lewis Publishers, Chelsea, MI (1987).
- ↑ 2.0 2.1 Keith, L. H. Environmental Sampling and Analysis: A Practical Guide, Lewis Publishers, Chelsea, MI (1991).
- ↑ Leidel, N. A., K. A. Busch, and J. R. Lynch. Occupational Exposure Sampling Strategy Manual, U.S. Department of Health and Human Services, Publ. (NIOSH) 77–179 (1977).
- ↑ Leidel, N. A. and K. A. Busch. Statistical Design and Data Analysis Requirements, Chapter 3 in L. V. Cralley and L. J. Cralley, Eds., Patty's Industrial Hygiene and Toxicology, Vol. III, 2nd Edition, Theory and Rational of Industrial Hygiene Practice. John Wiley & Sons, NY (1984).
- ↑ Garfield, F. M. Quality Assurance Principles for Analytical Laboratories, Association of Official Analytical Chemists, AOAC International, Arlington, VA (1991).
