Page:NIOSH Manual of Analytical Methods - 3600.pdf/4
MA NEB , Derm al Patch: MET HO D 360 0, Issue 1, dated 15 M arch 200 3 - Page 4 o f 5 CALCULATIONS: 18. From the calibration graph, read the concentration, C (µg/mL), of Maneb found in the sample. 19. Calculate the m ass, M, of M aneb in the sam ple (µg/sam ple).
CONFIRMATION: No confirm ation me thod has be en tested. Poss ible alternatives are ion-pairing chromatography with a C-18 colum n [5], or ana lysis of m ethylated de rivatives on a C-1 8 co lum n [3,4].
EVALUATION OF METHOD: This method has been evaluated in the laboratory only. No field samples have been analyzed to date. LOD/LOQ A s eries of m edia standard s (See N ote above un der s tep 13.d.) from 0.1 to 100 µg/mL were prepared in duplicate, analyzed, and fitted with a linear curve. The Limit of Detection (LO D), 0.02 m g/s am ple for a 40-mL desorbing volume, and Limit of Quantitation (LOQ), 0.066 mg/sample, were estimated using NIO SH SO P 01 8 [10]. PRECISION AND ACCURACY Twenty-four media standards were prepared, six at each of four levels: 3xLOQ, 10xLOQ, 30xLOQ, and 100xLOQ, as described above in Note under step 13.d. The m edia standards were desorbed with 40 m L of desorbing solution and analyzed. Levels 3xLOQ, 10xLOQ , and 100xLOQ were used to obtain a pooled relative standard de viation. One of the six sam ples at the 100xLO Q level was shown to be an outlier by Grubbs’ test and was not included in the calculations. Bias, Accuracy, and Overall Precision were not determined. The recoveries were all greater than 90% except for Level 3xLOQ, which was 88% [1]. STABILITY Stab ility studies were perform ed at 528 µg Maneb per dermal patch. At room temperature (24 / C), Maneb on dry Nu Gauze® patches was not stable, with less than 60% recovery on Day 2. At 4 / C, however, Maneb was stable on dry Nu Gauze® to at least Day 8. Maneb which was spiked onto Nu Gauze® and allowed to stand approximately two hours while the solvent dried and was then desorbed in a 1% L-cysteine, 3% Na 4EDTA solution, was stable to Day 22 with recoveries greater than 90% . At Da y 30 the reco very was 8 7% [1].
COM MEN TS: Most ethylene-bis-dithiocarbam ates (EBD C) containing divalent (or higher) metals (e.g., Maneb, Mancozeb, and Zineb) dissolve with difficulty in alm ost every so lvent. If the m etal ion is rem oved by co m plexation w ith E DT A (at hig h pH), the EBDC will dissolve but will begin to degrade rapidly, presumably by oxidation, to dis ulfides or o the r products. Adding an antio xidant su ch as L-c yste ine gre atly inhibits th is oxidative degradation. Ex cluding headspace air h as been show n to assist in re ducing oxidatio n; however, coo ling to 4 / C is one of the most important factors in sample preservation.
NIOSH Manual of Analytical Methods, Fourth Edition