Page:NIOSH Manual of Analytical Methods - 9106.pdf/7

 METHAMPHETAMINE. . .on Wipes by Liquid-Liquid Extraction: METHOD 9106, Issue 1, dated 17 October 2011 - Page 7 of 31

V1 = volume correction factor (needed only when the volume of internal standard V2 spiking solution used for spiking the samples – such as for composite samples requiring larger desorption solution volumes – is different from that used for spiking the calibration standards). (See Table 7, footnote 4.)

V1 =  volume in μL of internal standard spiking solution used to spike samples. V2 =  volume in μL of internal standard spiking solution used to spike the standards.

V3 = dilution factor, if applicable V4 V3 = 10 mL (volume of desorbate taken for cleanup in step 8). V4 = volume in mL of desorbate actually taken for cleanup and diluted to 10 mL with blank desorbing solution containing internal standard. b = concentration in media blank (in μg/sample determined from the calibration curve). V5 = volume correction factor for the media blank (needed only if the volume of V2 internal standard spiking solution used for spiking the media blank is different from that used for spiking the calibration standards.) V5 =   volume in μL of internal standard spiking solution used to spike media blank. 20.	Report concentration, C’, in μg per total area wiped (in cm2) as follows:

C’=

C A

Where: C = μg/sample (step 19). A = Total area wiped in cm2 per sample. NOTE:	 For example, if the sample was a composite sample and the area was 400 cm2, report results as μg/400 cm2 and not averaged to μg/100 cm2. In general, if the area wiped was greater than or less than 100 cm2, do not convert value to μg/100 cm2. To avoid confusion, report separately both μg/sample (C) and the total area wiped in cm2 per sample (A) for both discrete and composite samples. EVALUATION OF METHOD: This method was evaluated for those analytes listed in Tables 8a and 8b over a range of approximately 0.1 μg/sample to 30 μg/sample. These concentration levels represent approximately the 1 through 300 times the limit of quantitation (LOQ) level for most of the analytes [8]. Results are reported in the Backup Data Report for NIOSH 9106 [1]. The limits of detection (LOD and LOQ) were determined by preparing a series of liquid standards in desorption solution, processing them through the liquid-liquid extraction procedure of NIOSH 9106, and analyzing in both the scan and SIM modes. The LODs were estimated using the procedure of Burkart [8]. An LOD of 0.05 μg/sample for methamphetamine on wipes was achieved in either scan or SIM mode. The LOD was set at 0.05 μg/sample because that was the level of the lowest calibration standard for the LOD study. Lower LODs (e.g. 0.02 μg/sample) have been achieved in practice by including calibration standards at lower concentration levels. The cleanliness and performance of the mass spectrometer must be maintained such that at 0.1 μg/sample, a signal of at least 5 to 10 times the baseline noise is achievable. This is more easily accomplished in the SIM mode with the mass spectrometer. Six different wipe media were evaluated. These were 3”×3” 12-ply cotton gauze, 4”×4” AlphaWipes® (TX® 1004), 4”×4” 4-ply NU GAUZE®, 4”×4” 4-ply MIRASORB®, 4”×4” 6-ply SOF-WICK®, and 4”×4” 4-ply TOPPER® sponges. Results are given in the Backup Data Report [1]. No synthetic media performed NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

Method rev. 1.1.1