National Institute for Occupational Safety and Health

“ C. I. Direct Brown 95, 24.3 to 243 μg dye per sample, 78.5% recovery ( Sr = 6.7%) ; C. I. Direct Black 38, 12.5 to 250.0 μg dye per sample, 78.1% recovery ( Sr = 12.8%) . The pooled precisions ( Sr) for samples at three concentrations in the measurement range for each dye are as follows: Direct Red 28, 0.045; Direct Blue 6, 0.061; Direct Brown 95, 0.072; Direct Black 38, 0.078. Since the method does not distinguish between various benzidine-based dyes, recovery correction factors cannot be applied unless a single known dye is contained on the filter. ”

“ Prepare three filters at each of five concentration levels. c. Analyze the filters by steps 3 through 9 and 12 through 14. d. On the day of analysis of the filters, add the same volume of dye solution which was spiked onto the filters to 2.0 mL H 2O. Reduce this solution (steps 7 through 9) and analyze together with samples and standards (steps 12 through 14) . e. Calculate recovery (μg benzidine, o-tolidine, or o-dianisidine recovered from the filter/μg from step 11.d) . f. Prepare graph of recovery vs. μg benzidine, o-tolidine or o-dianisidine recovered. ”

“ The metho d will not distinguish benzidine obtained from reduction of the dyes and free benzidine in the dye formulation.
INTERFERENCES: Aniline, azobenzene, p-aminophenol, p-phenylenediamine or p-nitroaniline do not interfere in the measurement when present in equimolar amounts.
OTHER METHODS: This revises P&CAM 325 [2,3] . P&CAM 234 [4,5] , a general colorimetric method for diazonium salts and azo dyes, has not been revised. ”