# NIOSH Manual of Analytical Methods/Chapter C

​C. QUALITY ASSURANCE by David L. Smith, CIH; Michele L. Bolyard, CIH; and Peter M. Eller, Ph.D., CIH
| | Contents: | Page |
| 1. | Role of Laboratory Quality Assurance Program | 7 |
| 2. | Organization | 8 |
| | a. Quality Assurance Coordinator | 8 |
| | b. Sample Clerk | 9 |
| 3. | Quality Assurance in Sampling | 9 |
| 4. | Quality Assurance in Measurement | 10 |
| | a. Methods | 10 |
| | b. Standards | 10 |
| | c. Blanks | 11 |
| | d. Blind Samples | 11 |
| | e. Recovery Studies | 12 |
| | f. Duplicates | 12 |
| 5. | Interlaboratory Testing | 12 |
| 6. | Reporting | 13 |
| 7. | Laboratory Notebooks | 13 |
| 8. | Instrument Maintenance | 14 |
| 9. | Sample Tracking | 15 |
| 10. | Quality Assurance Records | 15 |
| 11. | References | 15 |
1. ROLE OF LABORATORY QUALITY ASSURANCE PROGRAM
Analytical data are used to make a variety of decisions, i.e., to decide whether a particular chemical agent is present in a workplace atmosphere, whether a hazard to workers' health exists in that atmosphere, or whether a workroom atmosphere complies with applicable standards. Errors in such data can have a variety of costly effects. The consequences of erroneous data may lead to the wrong decision being made as to whether a non-compliance situation exists. If the analytical results are a part of a larger experiment, perhaps the wrong conclusion might be reached or the results might be uninterpretable. If the presence or absence of a particular agent is erroneously reported, a threat to workers' health may be allowed to continue. It is the role of a laboratory's quality assurance program to provide the necessary safeguards to minimize these occurrences and to provide a means of detecting errors when they do occur. There are many good texts and articles addressing the subject of laboratory quality control. The purpose of this chapter is to address some of the ​aspects of quality control as they relate to industrial hygiene laboratory quality control.
It is not possible to design a quality assurance program to fit all laboratories since no two laboratories serve the exact same purpose or operate in exactly the same manner. Each laboratory must set its own operating procedures and quality control practices, and document them in a Quality Assurance Manual. This chapter, therefore, will not set forth concrete recommendations for implementing a quality assurance program, but rather will present aspects of laboratory quality assurance and quality control which should be addressed by each laboratory.
A successful quality assurance effort cannot be achieved through the efforts of only one individual. A laboratory’s quality assurance coordinator needs the assistance and cooperation of all laboratory personnel to be effective. To this end, it is necessary to discourage adversarial relationships between quality control personnel and bench chemists. Analysts must be trained and made aware of the purpose and value of quality assurance functions and, in turn, the quality assurance program must be designed so that its functions are based on sound goals directed toward improving the performance of both the individual analyst and the laboratory as a whole.
Frequently, analytical results are challenged months or years after the analysis is complete. In order to support the original data, an effective, complete, record-keeping system must be maintained. Another chemist must be able to reconstruct the exact treatment to which the samples were subjected solely from a laboratory’s records. Furthermore, if the appropriate quality control checks were performed with the analysis and documented, there can be no doubt regarding the results.
2. ORGANIZATION
A laboratory, just as any other organization, should have a clearly defined organizational structure. Responsibilities of each member of the laboratory staff should be in writing and understood by all. In this way, confusion regarding tasks which need to be performed can be avoided.
The specific organizational structure of the laboratory will vary, depending on the laboratory’s function. Two functions which relate to quality assurance should be assigned in every laboratory: the quality assurance coordinator and the sample clerk. The size and nature of the laboratory may preclude assignment of a full-time position to these functions; however, a laboratory member should be assigned these duties and it should be understood that they are to have top priority.
* Quality Assurance Coordinator The quality assurance coordinator's functions will depend on the size and nature of the laboratory. This professional has overall responsibility for assuring that reported data meet established standards for precision and accuracy and that these results can be supported scientifically by the various quality control checks performed with the analysis. One of the major functions of this individual is to perform audits of the quality control system and to implement changes that eliminate recurring errors.</noinclude> ​The quality assurance coordinator should not be under the direct supervision of management responsible for day-to-day laboratory operation. In this way, conflicts between the laboratory’s dual responsibilities of providing analytical results in a rapid fashion while maintaining quality can be avoided. The quality assurance coordinator should also serve as a resource person for chemists or managers on questions or problems related to quality assurance and should have a working knowledge of statistics, including quality control charting, and experimental design.
* Sample Clerk The sample clerk's functions will also vary, depending on the size and function of the laboratory. As a minimum, the sample clerk is responsible for the receipt and log-in of samples. Field samples should be stored in a secure location under proper conditions (temperature, etc.) until analysis. Logging and tracking of samples in the laboratory is important so that the history of these samples can be documented and processed in a timely manner. The sample clerk may also be given the responsibility of maintaining chain of custody documentation.
3. QUALITY ASSURANCE IN SAMPLING
Quality assurance procedures should not be overlooked by personnel performing field sampling. The field sampling parameters often have more effect on precision and accuracy of the final result than parameters of the measurement. Field personnel should become familiar with sampling and measurement methods which they will use. The methods usually specify the proper sampling media to be used, the correct flow rate and sample volume, as well as special precautions on sample handling, shipping and possible interferences.
Sampling equipment must be maintained in reliable working order. It is desirable to have one person or group given responsibility for the care, maintenance and stocking of field sampling equipment. This person or group should periodically inspect and repair all equipment and keep track of the use and location of sampling equipment when it is signed out. Sampling pumps should be calibrated with each use. This calibration should be performed with the sampler in line. Since differences in pressure drop across the sampler will affect flow rate, it may be necessary to perform the calibration with the actual sampler to be used.
The exact sampling time must be known in order to accurately estimate the sampled volume. Recording only the start and stop time assumes that the pump functions properly over the entire sampling period. Occasional spot checks for proper operation should be made throughout the sampling period.
Since many modern analytical techniques are extremely sensitive, special care must be taken to avoid contamination of field samples. Samples must not be stored or shipped with bulk materials which ​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. 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 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 ​generated samples, the stability of collected samples or possible interferences to accurate use of the method. Methods should be tested for ruggedness so that critical steps in the analysis can be identified. Experimental designs have been published which permit rapid evaluation of a number of factors involved in the analysis (e.g.,).
* Standards Standard solutions may be for either identification or quantitation of the analyte of interest. The bulk material used for preparation of standards should be of sufficient purity to avoid errors in the identification or quantitation. Where available, Standard Reference Materials (SRMs available from the U.S. National Institute of Standards and Technology) or other well-characterized standards are useful for assuring that results are consistent with other organizations and agencies. Laboratory reagents and standards should also be properly labelled with contents, and receipt and expiration dates. For quantitation, sufficient numbers of standards should be prepared so that adequate confidence intervals on reported values can be obtained. As a guideline, we recommend that calibration curves be prepared with triplicate points at each of at least five different concentration levels. The standard curve should be prepared so that linearity can be assured over the range of the curve. Also, it is important that the concentration of standard solutions be chosen to bracket the actual samples. In this way, extrapolation outside the range of standards is avoided. The concentration of standard solutions should be chosen to be consistent with the purpose of the sampling. That is, if it is desired to demonstrate whether exposure standards are being met, then the standard curve should be constructed to bracket the concentrations which would be encountered at or near the applicable exposure standard. If it is desired to demonstrate whether a compound is present in the atmosphere being sampled, then the calibration curve should be constructed closer to the limit of detection. During measurement, working standards should be interspersed with field samples. In this way, it should be possible to detect if instrument drift becomes significant. Internal standards are useful for correcting instrument response for the actual amount of sample injected into a chromatograph. The internal standard should be chosen so that its retention time is reasonably close, without peak overlap, to the peak of interest.
* Blanks (also see page 26) A particular analysis may involve several types of "blank" measurements including reagent blanks, media blanks or field blanks. Reagent blanks measure the signal contribution from solvents, acids or other reagents used by the laboratory in preparing samples for analysis. Media blanks measure the signal contribution from the collection media (impinger solution, filter, sorbent tube, etc.) and field blanks measure signal contribution of the media plus any contamination which may have occurred during handling, shipping and storage before analysis. The nature and number of blank measurements will depend on the method and circumstances, but the purpose of all blank measurements is to help prevent errors in identification and quantitation of field samples.
* ↑ Hunter, J. S. "The National System of Scientific Measurement," Science, 210. 869 (1980).
* ↑ Garfield, F. M. Quality Assurance Principles for Analytical Laboratories, Association of Official Analytical Chemists, AOAC International, Arlington, VA (1991).
* ↑ Taylor, J. K. Quality Assurance of Chemical Measurements, Lewis Publishers, Chelsea, MI (1987).
* ↑ Keith, L. H. Environmental Sampling and Analysis: A Practical Guide, Lewis Publishers, Chelsea, MI (1991).
* ↑ Dux, J. P. Handbook of Quality Assurance for the Analytical Chemistry Laboratory, Van Nostrand Reinhold, New York (1986).
* ↑ Kratochvil, B. and J. K. Taylor. "Sampling for Chemical Analysis," Anal. Chem., 53, 924A–938A (1981).
* ↑ Cali, J. P. and W. P. Reed. Accuracy in Trace Analysis: Sampling, Sample Handling, Analysis, NBS Spec. Publication 422, Vol 1, 41 (1976).
* ↑ Kosta L. Talanta, 29, 985–992 (1982).
* ↑ 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).
* ↑ Youden W. J. and E. H. Steiner. Statistical Manual of the Association of Official Analytical Chemists, AOAC, Washington, DC (1975).
* ↑ Taylor, J. K. Statistical Techniques for Data Analysis, Lewis Publishers, Chelsea, MI (1990).
* ↑ DeVoe, J.R., Ed. ACS Symp. Ser. No. 63, American Chemical Society, Washington, DC (1977).
* ↑ Shulman, S.A., J.H. Groff, and M.T. Abell, "Performance of Laboratories Measuring Silica in the Proficiency Analytical Testing Program," Amer. Ind. Hyg. Assoc. J., 53: 49-56 (1992).
* ↑ American Association for Laboratory Accreditation, A2LA 1993 Directory of Accredited Laboratories, Gaithersburg, MD (1993).
* ↑ Keith, L.H. Environmental Sampling and Analysis: A Practical Guide, Lewis Publishers, Chelsea, MI (1991).
* ↑ Taylor, J.K. Statistical Techniques for Data Analysis, Lewis Publishers, Chelsea, MI (1990)
* ↑ Kelley, W.D., T.A. Ratcliff Jr., and C. Nenadic. Basic Statistics for Laboratories - A Primary for Laboratory Workers, Van Nostrand Reinhold, New York (1992).
* ↑ Kanare, H.M. Writing the Laboratory Notebook, American Chemical Society, Washington, DC (1985)