National Institute for Occupational Safety and Health

“ Concentration of TEA = 0.2 mM, water = 0.2%, and internal standards = 120 μg/mL. Stableup to 30 days at 0 to 4 °C. 10. Individual analyte stock solutions, 5 mg/mL. Add each analyte to acetonitrile in separate volumetric flasks. Use methylene chloride for benomyl and carbendazim. Use 50/50 v/v methanol/acetonitrilefor formetanate. Store at –12 ± 1 °C. (Solutions are stable up to 30 days.) 11. Calibration stock solution. Combine stock solutions of analytes of interest in a volumetric flask to produce the highest concentration standard (suggest 120 to 480 μg/mL) . ”

“ Some analytes (O-aryl carbamates especially) can be confirmed by GC/MS using highly deactivated injection ports and analytical GC columns, or by HPLC/MS.
EVALUATION OF METHOD: This method was evaluated over the ranges specified in Table 2 at 25 °C with 240-L air samples. Samplers were tested at 15 and 80% relative humidity and 10 and 30 °C. In these experiments, test atmospheres were not generated; instead, analytes were fortified on the face of the sampler filters. The conditioned air was pulled through the samplers at 1 L/min for four hours. ”

“ If the baseline is rising, a background selected from the backside of the peak may induce losses of absorption in the region below 210 nm. Conversely, one selected from in front of the unknown HPLC peak may add to this region of the spectra. It is better to get an averaged background first. Spectra maxima should match within a few nanometers. Relative absorbance at each maxima may vary, even after background subtraction, depending upon the concentration of the analytes and the characteristics of different scanning UV detectors. ”

“ Dead volumes can cause the method to fail seriously. Important areas to look for are larger bore and longer-than-necessary transfer lines between the sample injector and the analytical column [15] . Another area of potential large dead volumes are poorly designed or connected guard columns and sample injectors. 7. UV Wavelength Selection a. The wavelengths specified in this method are a best compromise for all of the analytes listed in Table 1. There are maxima for each of the pesticides that would give greater sensitivity and/or signal-to-noise ratio. ”

“ Water, however, is deleterious to several of the analytes specified in this method (see note A17 above) . Therefore, an acceptable alternative is to inject very small volumes, not greater than 5 μL [31] , of the desorption solvent (acetonitrile in this method) on a high-resolution HPLC column. If it is known that only analytes that are stable in aqueous solutions are to be determinede.g., ( oxamyl and methomyl, but not formetanate or captan) , the desorbates may be diluted with water and larger volumes injected. ”

“ Use of an internal standard is recommended [1,16] , but optional if the precision of the injection device and HPLC system are known to be adequate. 11. Prepare desorption efficiency (DE) samples and Laboratory Control Samples (LCS) with each sample set at a rate of 10% of samples. a. Remove cap and the PTFE retainer ring from large end of sampler tube (to prevent wicking behind the ring) . Apply known volume of calibration solution to face of quartz fiber filter. NOTE: Spike no more than 15 to 30 μL at a time. ”

“ Actual RIs need to be established for each set of conditions. Compounds that are ionic under elution conditions or that interact strongly with polar sites on the column will have the most variable retention times and retention indices. 2. By Second Column. The cyanopropyl stationary phase strongly induces some exchanges in elution orders and alters relative spacings between adjacent analytes in the chromatogram that may be useful in confirmations. 3. By Alternate Solvent. ”

“ 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. ”

“ By diluting with water, sharper peaks may be obtained for early eluting compounds with accelerated elution conditions such as the use of shorter HPLC columns, higher percentages of organic modifier, or higher percentages of mobile phase B in the initial conditions. ”

“ No serious problems are expected to be encountered. 8. Diuron: The breakdown product of carbaryl, 1-naphthol, elutes immediately after diuron under the conditions given. On certain columns, it may coelute with diuron, giving false positive responses. The retention time of 1-naphthol relative to diuron must be determined for any particular column if carbaryl is anticipated to have been present in the sample. 9. Formetanate a. At analytical concentrations formetanate is not stable either in methanol or in aqueous mixtures of methanol or acetonitrile with or without chloroacetic acid. ”

“ The basic compounds (benomyl, carbendazim, and formetanate) present special challenges that are easily overcome with highly inert or base-deactivated columns [26] . The addition of TEA-PO4 buffer to mobile phase A also greatly improves performance for these compounds [16, 26, 27] . c. Dimensions: A longer column (300 mm) was used in this method in order to improve resolution for a large number of analytes and interferences, expected and unexpected. Long columns have higher operating pressures ”

“ Buffer concentration should be 0.01 to 0.05M. The concentration and pH of the bufferhad a great effect on exact retention time of formetanate. 5. Dwell Volumes: Dwell volumes can affect the retention times and peak shapes of analytes. This is internal volume of the system from the point of mixture of the mobile phases A and B to the head of the column. It includes the volume of the transfer lines; any in-line filters (which should be between the pump and the sample injector if at all, and definitely not after the sample injector) ; the sample injector; the guard column ”

“ Program rate Program time (min) Program type Final hold time (min) Flow rate (mL/min) Column temperature ( C) Dwell volume (mL) Injection volume (μL) Injection solvent
A B
C
D
Ligand density (micromole/m2) is a better description of surface coverage than % carbon loading [22,23] . Choice of alcohol modifier is not critical. Percentages may be varied to adjust retention times andpeak shapes for early eluting analytes. Reequilibration time may be shorter with 1-propanol [24-26] . Buffer is very essential for basic analytes such as Formetanate, Carbendazim, and Benomyl [12,27,28] . ”

“ If only two wavelength channels are used (225 nm and 200 nm) , the response for aldicarb at 200 nm should be monitored (refer to UV spectrum for aldicarb) . At 205 nm the signal will be smaller, but the signal-to- noise ratio may be better on particular instruments. An alternative but lesser maximum is at approximately 245 to 246 nm. This latter maximum, though small, may have less background noise and interferences from coelutants. b. Aldicarb is a highly toxic pesticide. Care should be exercised in handling pure stock material. 2. Benomyl (see also Carbendazim) a. ”