4,4'-METHYLENEDIANILINE: METHOD 5029, Issue 2, dated 15 August 1994 - Page 3 of 5 SAMPLE PREPARATION: 6. 7.
Agitate the samples for 1 hour in an ultrasonic water bath. Filter the sample solution through a 0.45-µm PTFE filter and a disposable syringe into a clean vial.
CALIBRATION AND QUALITY CONTROL: 8.
Calibrate daily with at least six working standards over the range of interest. a. Make serial dilutions as needed to obtain MDA concentrations in the range 0.025 to 1 µg/mL. b. Analyze together with samples and blanks (steps 11 through 13). c. Prepare a calibration graph (peak area vs. concentration of MDA, µg per sample) for each detector (UV and ECHD). Determine the recovery at least once for each lot of filters used for sampling in the range of interest. Prepare six filters at each of three concentration levels plus three media blanks. a. Add known amounts of MDA in methanol to the filters, using a microliter syringe. b. Cover filters. Allow to stand overnight for solvent evaporation. c. Extract with 4.0 mL extracting solutions, prepare samples (steps 6 and 7) and analyze (steps 11 through 13) together with standards and blanks. d. Determine recovery (R). Construct a graph of R vs. µg MDA recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and recovery graph are in control.
9.
10.
MEASUREMENT: 11.
Set liquid chromatograph to manufacturer's recommendations and parameters given on page 5029-1. Inject sample aliquot manually or with autosampler. Measure peak areas for UV and ECHD responses.
12. 13.
CALCULATIONS: 14.
Determine the mass, µg (corrected for recovery) of MDA found on the sample filter (W) and in the average blank filter (B). Calculate concentration (C) of MDA in the air volume sampled, V (L):
15.
EVALUATION OF METHOD: A calibration curve for the UV absorption detector was constructed from 8 standards over the range 0.03 µg/mL to 1.22 µg/mL [1]. The curve was linear over this region and the LOD was determined to be 0.03 µg/mL. A calibration curve for the ECHD over the range 0.001 µg/mL to 0.12 µg/mL was linear and the LOD was determined to be 0.002 µg/mL. Test samples were prepared by spiking acid-impregnated filters with known amounts of MDA from a solution in methanol. Samples were prepared in triplicate at levels between 0.009 µg per filter and 3.7 µg per filter. (See Table 1 for results): a.
To evaluate extraction efficiency, the filters were analyzed immediately.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
