Page:NIOSH Manual of Analytical Methods - 5022.pdf/3

 ARSENIC, organo-: METHOD 5022, Issue 2, dated 15 August 1994 - Page 3 of 6 SAMPLING: 1. 2. 3.

Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 3 L/min for a total sample volume of 50 to 1000 L. Cap the cassettes and pack securely for shipment.

SAMPLE PREPARATION: 4. 5. 6.

For each sample, pipet 25 mL Eluent A into a clean 50-mL beaker. Open the cassette, remove the PTFE filter with clean forceps, and transfer it to the beaker. Place the exposed side of the filter in contact with the solution. Cover beaker. Agitate contents of the beaker for 30 min in an ultrasonic water bath. If the extracts will not be analyzed immediately, store at ca. 4 °C until measurement.

CALIBRATION AND QUALITY CONTROL: 7.

Calibrate daily with at least six working standards over the range 0.2 to 2 µg As per sample (0.008 to 0.08 µg As/mL). a. Add known amounts of calibration stock solution to Eluent A in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with the samples and blanks (steps 8 through 12). c. Prepare calibration graph for each arsenic species (peak area or height vs. µg As).

MEASUREMENT: 8.

9.

Set the ion chromatograph to the conditions given on page 5022-1. Allow the columns to equilibrate with eluent ≥1 h before connecting effluent to the arsine generator. NOTE: Eluent A allows the separation of methylarsonic acid (t r = 2 min), p-aminophenylarsonic acid (t r = 4 min), and As(V) (t r = 7.5 min); As(III) and dimethylarsenic acid (t r = 1 min) are not resolved. If a signal is obtained at the approximate retention time of the latter two compounds, or if both compounds are known to be present in the sample, perform a second analysis using Eluent B (lower ionic strength). If either of the two compounds is known not to be present, Eluent A will effectively determine the remaining compounds. With Eluent B the other species have very long retention times and will accumulate on the column, tying up active resin sites. Therefore, flush the column with Eluent A after each 10 to 15 samples and reequilibrate with Eluent B before further analysis. Connect the IC effluent to the arsine generator into which the following flow: Saturated K 2S2O 8 solution: NaBH 4 solution: Ar carrier gas:

10.

11.

0.8 mL/min 2.0 mL/min 300 mL/min

NOTE: The gaseous arsines formed in the arsine generator are first separated from liquid solution using the gas-liquid separator (Figure 2) and then transferred by argon carrier gas through PTFE tubing to the heated quartz furnace. Set the AAS according to manufacturer's recommendations and to the conditions given on page 5022-1. Align the quartz cell in the optical path. Heat the quartz cell gradually to 800 °C using a variable transformer and thermocouple. Using a syringe, inject a sample aliquot ( ca. 2 to 3 mL) into the chromatograph, flushing the injection loop to avoid contamination from the previous injection. Rinse the syringe with deionized water and dry it between samples, or use disposable syringes. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94