Page:NIOSH Manual of Analytical Methods - 9111.pdf/12

 METHAMPHETAMINE on Wipes by LC/MS : METHOD 9111, Issue 1, dated 17 October 2011 - Page 12 of 12

the gauze is facing inward. Using a fresh surface of the gauze, wipe or blot the area again with at least five overlapping top-to-bottom vertical passes beginning at the left side and progressing to the right in an “N” pattern. If blotting, blot at least five times on each vertical pass. Roll or fold the gauze again and insert into the shipping container. Blotting is suggested in areas so soiled or rough that the threads of the gauze media are continually snagged. NOTE: On areas larger than 100 cm², more than five passes and blots will be needed. c.	 Repeat or Serial Wiping: If isopropanol is used for wiping, a serial or repeat wipe sample of the same area with a fresh gauze wipe will improve sampling efficiency. For serial wiping, repeat the wiping procedure described above (APPENDIX 7a or 7b) with a fresh gauze wipe. Place the second gauze wipe into the same shipping container as the first gauze. The 50-mL polypropylene centrifuge tubes are large enough to contain up to two gauze wipes of either the 3” x 3” 12-ply or 4” x 4” 8-ply sizes. NOTE:		 If the area to be wiped remains substantially wet from the first gauze, the second gauze wipe might be used in the dry state to soak up the residual solvent from the first gauze wipe. 8.	Cap shipping containers securely and keep refrigerated (<6 °C). Make sure caps are not crossthreaded. Containers must have no chips, fractures, or other irregularities on the sealing edge. Do not use polyethylene plastic bags. While methamphetamine and several related amines are stable on the recommended wipe media for at least 7 days at room temperature, refrigeration is recommended as soon as possible. 9.	Label each sample clearly with a unique sample identification number or name, and the date, time, location, and initials or identification number of the individual taking the sample. The above information and a description of the sample and the area wiped should also be recorded in a logbook for later correlation with the analytical results. SAMPLE PREPARATION Samples requiring pH adjustment: If there is reason to believe that the samples may be alkaline enough to overcome the acidity of the desorption solution (e.g. wipes of unpainted concrete or stucco surfaces), then the pH must be adjusted to about ≤ 4. The pH may be checked with pH paper or monitored with the addition of about 2 drops of the mixed pH indicator solution of bromothymol blue and phenolphthalein. (The color should be yellow and not green or blue.) The preparation of this indicator solution can be found in NIOSH 9106 or NIOSH 9109. [2, 3] If the pH needs to be adjusted, a solution of dilute (2.5 to 3 M) sulfuric acid is used and added dropwise. Mix the contents by shaking or inversion a few times by hand after each addition of acid before checking the pH.

Method rev. 1.1.1

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition