METHAMPHETAMINE . . .on Wipes by Liquid-Liquid Extraction: METHOD 9106, Issue 1, dated 17 October 2011 - Page 5 of 31
NOTE: The dark color of the crystal violet helps make the residue more visible when it is dried. If at least 0.1 mL of isopropanol was present in the eluates, the crystal violet will also go through a series of color changes that helps in monitoring the drying process. b. To each dried sample, add 100 μL of chlorodifluoroacetic anhydride and recap tubes. Mix the contents by vortexing briefly. NOTE 1: It is recommended that the tubes be kept capped and to only uncap about 5 at a time for the addition of the derivatizing reagent. Do not leave the acid anhydride bottle open between taking aliquots since the reagent is moisture sensitive. NOTE 2: If incomplete derivatization is routinely experienced, increase volume of reagent to 150 or 200 μL. The color of the crystal violet will turn yellow or yellow-green with the addition of chlorodifluoroacetic anhydride. c. Heat in an oven at 70-75 °C for 20-30 minutes. d. After heating, allow the tubes to cool to room temperature. Remove caps and evaporate the contents to dryness under a stream of nitrogen at room temperature. As the solution concentrates it turns from a yellow or yellowish-green solution to a bluish-green just before going to dryness. At the point of dryness the color of the residue normally turns rapidly to blue or violet, depending upon the amount of coextractants (the more co-extractants, the more blue the color and the less likely a violet color will develop). Remove the tubes just as soon as the blue or violet color becomes apparent. Losses have been experienced if blowing is continued for more than 2 minutes beyond the blue or violet color stage. NOTE: If an oil-like residue or film persists, then the sample may have too many contaminants that were not removed at the cleanup step or were introduced subsequent to cleanup. In such a case, return to step 7f and perform the clean-up (step 8) on another 10-mL aliquot of the sample desorbate using methylene chloride as the cleanup solvent instead of hexane. Discard the (lower) organic layer to waste before proceeding to steps 9 through 11. e. Reconstitute the dried residue with 1 mL of the reconstitution solvent. The reconstituted solution normally will become deep blue in color. Mix by vortexing briefly a couple of times. Transfer the solutions to 2-mL amber-colored GC vials containing 200 to 250 mg anhydrous sodium sulfate. Cap vials, label, and analyze by GC/MS (See MEASUREMENT, steps 15-17). NOTE: Derivatives of phenylpropanolamine (norephedrine) break down significantly over several days at room temperature. GC vials containing derivatives should be kept refrigerated until analysis. CALIBRATION AND QUALITY CONTROL: 12. Determine retention times for the derivatives of the analytes of interest using the column and chromatographic conditions specified on page 9106-1. Table 10 gives typical retention times for various drugs, precursors, and adulterants. 13. Calibrate daily with at least six calibration standards plus a blank (CS0) selected from Table 7 to cover the analytical range. a. Prepare the analyte spiking solution as follows: Add known amounts of individual drug stock solutions to a volumetric flask and dilute to volume with methanol. A recommended final concentration for this solution is approximately 200 μg each per mL. b. Prepare calibration standards and media blanks in clean shipping containers (e.g. 50-mL polypropylene centrifuge tubes or equivalent). NOTE: Liquid standards (standards without added blank wipe media) may be prepared in lieu of media standards if cotton gauze was used for the samples. c. Add 3 mL methanol (or isopropanol if isopropanol was used with the samples in the field) to each calibration standard and media blank.
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition
Method rev. 1.1.1
