Page:NIOSH Manual of Analytical Methods - 5601.pdf/20

 ORGANONITROGEN PESTICIDES: METHOD 5601, Issue 1, dated 15 January 1998 - Page 20 of 21 3. Industrial Chemicals (Plastic and Rubber Additives) a. Several plasticizers might elute in the window of interest depending upon the selection of column and conditions. These include diethyl and dibutyl phthalates. Dibutyl phthalate is typically found in polyvinyl gloves, flexible tubing, and in coatings on bottles and tool handles. Contact with these materials should be avoided or documented. Other plasticizers, such as dioctyl phthalate and bis-ethylhexyl adipate, have late elution times and will elute after about 30 minutes under the conditions specified. However, if the run times are shortened, these may be carried over on-column to subsequent analyses, causing interferences. b. Common antioxidants such as BHT (2,6-di-tert-butyl-4-methyl phenol) also elute late and may be carried over on-column, creating interferences in subsequent analyses. 4. Other Pesticides: Spray mixtures very often contain a mixture of pesticides. It is not uncommon to find chlorpyrifos, an organophosphate, or a pyrethroid pesticide in combination with propoxur, for example. Both of these noncarbamate pesticides can be detected under the conditions of the method. The retention time and spectra of chlorpyrifos is included for qualitative purposes. Most pyrethroids elute later than most of the carbamates; if present, they may elute in a subsequent run if run times are too short. It is also not uncommon to mix herbicides of different classes such as diuron with bromacil, atrazine, or 2,4-D. Because of this possibility, retention times and spectra of other common herbicides are also provided in Table 4 for qualitative purposes. 5. Miscellaneous Chemicals: There are a number of chemicals which elute in the retention time window of interest for carbamates and urea pesticides and may, with particular columns or conditions, interfere with analytes of interest. The presence or the known use of these compounds or their sources should be documented as part of the sample history. Table 4 lists a few of the compounds, which include the following. a. The common insect repellent, DEET (N,N-diethyl-meta-toluamide). Since DEET may be heavily used by outdoor workers, its presence on exposed areas of the skin or clothing may contribute to sampler contamination either through direct contact with the face of the sampler or through collection of vapors if the sampler is in close proximity to areas of application or is exposed to overspray during application from a spray can or bottle. b. Inadvertent collection of tobacco side-stream smoke may introduce potentially interfering compounds, one of which is nicotine. c. Compounds in beverages used during work periods, which include at least caffeine. E. SAMPLER 1. The OVS-2 Sampler. The OVS-2 (OSHA Versatile Sampler with XAD-2) combines both filter and XAD-2 sorbent in one unit. The filter is necessary to trap submicron aerosols that would pass through the XAD-2 bed. Substitutions should not be made. 2. Quartz Fiber and Glass Fiber Filters (GFF). The OVS-2 tubes are available with either glass or quartz fiber filters. OSHA Methods specify GFF. This method specifies a quartz fiber filter. For analytes being desorbed with acetonitrile, no difference in desorption efficiency was observed between glass fiber and quartz fiber filters. Therefore, the tubes may be interchanged for the analytes specified in this method. 3. Flow Rates. The OVS-2 sampler is designed for a flow rate of 1 L/min. At slower flow rates, 0.1 to 0.2 L/min, there may not be enough capture velocity for aerosols. 4. Applying Liquid Spikes. The Teflon® retainer ring should be removed when spiking the face of the OVS-2 tubes with more than approximately 10 µL, in order to prevent wicking of the carrier solvent behind the ring and consequent loss of standard. Volumes of spiking fluid greater than 15 to 30 µL will flood the XAD-2 sectionand possibly wick into the back-up section. Whenever more than 15 to 30 µL is to be applied to the tubes, air must be drawn through the tubes at approximately 1 L/min during the spiking procedure andthe solvent added in 15- to 30-µL increments with a few minutes between each addition allowed for drying of the solvent. F. CONFIRMATION NIOSH Manual of Analytical Methods, Fourth Edition