Eugene R. Kennedy, Ph.D., Thomas J. Fischbach, Ruiguang Song, Ph.D., Peter M. Eller, Ph.D., Stanley A. Shulman, Ph.D., NIOSH/DPSE and R. DeLon Hull, Ph.D., NIOSH/DSHEFS

“ When attempting to generate a concentration of an analyte, the impact of environmental conditions, such as temperature, pressure, humidity, and interferences, on sampler performance and/or generation should be considered. The effect of elevated temperature on the collection medium of a sampler may decrease the capacity of the sampler or may decompose the analyte during generation and sampling. Reduced pressure may also reduce the capacity of a sampler. ”

“ Since industrial hygiene analytical methods are geared toward measuring personal exposure, the size, weight, and convenience of the sampler are important elements in sampler design. The personal sampler should allow freedom of movement and should be unobtrusive, unbreakable, and not prone to leakage. The pressure drop across the sampler should not be so great as to limit sample collection times to 10 h with personal sampling pumps. ”

“ Triplicate samplers at three different flow rates should be included to verify capacity at each of the six different humidity and temperature levels. For samplers which contain backup sampling media, only the front section of the sampler should be used. A means is required to quantitate analyte in the effluent from the sampler. This may involve the use of a backup sampler, continuous monitor or other appropriate means which can provide a measure of analyte concentration in the sampler effluent (ca. 1 - 5% of the influent concentration) . ”

“ These also aid in establishment of analyte purity. Potential sources of this information include chemical reference books, health hazard evaluation reports, bulk sample analyses, material safety data sheets, chemical process information, etc. Since innovation is a key element in the sampling and analytical method development process, detailed experiments for the initial development of the sampling approach and optimization of the analytical procedure are better left to the discretion of the researcher. ”

“ The bias and imprecision of the source measurements can be differentially affected by intermediate operations in producing the final estimate. For example, if the final estimate is a function of a single average of many source measurements, its bias is not affected by the averaging while imprecision is reduced as a function of the square root of the number of measurements. ”

“ High relative humidity in many instances has been observed to reduce sampler capacity [3] . In other instances it has increased sampler capacity [11] . A typical interference (s) should be generated along with the analyte to approximate a typical workplace sampling environment.
Generation of particulate material can be extremely complex [12,13] , especially if particles of a required size range must be generated for the evaluation of a specified sampler inlet design. ”

“ Also the precision and bias of the independent method should be homogeneous over the concentrations investigated. (See Reference 1 for the definitions of these attributes.) In instances where the concentration of the generator can be based only on calculations using flow rates in the generator and the amount of analyte injected, the generation system should be well characterized [1] so that analyte losses are minimized. ”

“ The use of potentially toxic reagents should be avoided unless they can be used safely. Reagents used should not pose any exposure hazard to the worker wearing the sampler or to the industrial hygienist taking the samples.
b. Recovery of the Analyte from the Medium During the course of method development experiments, the ability to recover the analyte from the sampling medium should be determined. ”

“ A concentration of 0.5 times the lowest exposure limit should be sampled with 30 samplers for a minimum of 1⁄2 the MRST. The humidity and temperature of the generator should be at the same level as defined in the sample capacity experiment to reduce sample capacity. ”

“ During development, it should be recognized that appropriate, statistically designed experiments will optimize the amount of information obtained. Therefore, consultation with a statistician about appropriately designed experiments will be of value during this phase of the research. ”

“ Analysis and reanalysis results should agree within 5% of each other.
c. Stability of the Analyte on the Medium An extension to the experiment described above may be performed to investigate potential stability problems early in the experimentation. An additional set of fortified samples at each of the 4 concentrations should be prepared and analyzed after 7-days' storage at room temperature. Recovery should be similar to the above results within experimental error. ”

“ Guidelines for Air Sampling and Analytical Method Development and Evaluation. NIOSH Technical report, (DHHS (NIOSH) Publication No. 95-117) Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Division of Physical Sciences and Engineering, 1995. ”

“ Performance of the NIOSH Charcoal Tube Technique for the Determination of Air Concentrations of Organic Vapors. Am. Ind. Hyg. Assoc. J. 38:476-486 (1977) .
[5] Posner, J., and J. Okenfuss: Desorption of Organic Analytes from Activated Carbon. Am. Ind. Hyg. Assoc. ”