Page:NIOSH Manual of Analytical Methods - 6008.pdf/3

 STIBINE: METHOD 6008, Issue 2, dated 15 August 1994 - Page 3 of 4 11. 12. 13. 14.

15.

Add 15 ± 5 mg ceric sulfate, swirl to dissolve and let stand unstoppered 60 s. Add 15.0 mL isopropyl ether to the funnel, stopper, and shake 30 s, releasing pressure only at the beginning and end of that period. Add 7.0 mL water, Shake 60 s. Wait 60 s to allow for separation. Remove and discard the aqueous layer. Be careful to remove all of the aqueous layer. Add 20.0 mL working Rhodamine B solution, shake 60 s, releasing pressure only at the beginning and end of that period. Allow 60 s for the phases to separate. Remove and discard aqueous (lower) layer. Drain ca. 10 mL of the remaining solution into a 15-mL centrifuge tube and cap tightly. Centrifuge 120 s at 2000 rpm. Transfer ca. 3 mL of the supernatant liquid to an absorption cell and cap. Proceed immediately to step 18.

CALIBRATION AND QUALITY CONTROL: 16.

17.

Calibrate daily with at least six working standards over the range 2 to 20 µg antimony per sample. a. Add known amounts of antimony stock solution and conc. HCl to cover the antimony concentration of 2 to 20 µg Sb per 15 mL and a reagent blank. b. Proceed as in steps 10 through 15 and 18 and 19. c. Prepare a calibration graph (absorbance vs. µg antimony/15 mL). Analyze three quality control spikes to ensure that the calibration graph is in control.

MEASUREMENT: 18. 19.

Set the spectrophotometer to manufacturer's recommendations and to conditions given on page 6008-1. Measure the absorbance using isopropyl ether as a blank.

CALCULATIONS: 20.

21.

Determine the mass, µg, of stibine found in the sample front (W f) and back (W b) sorbent sections, and in the average blank front (B f) and back (B b) sorbent sections by multiplying the mass of antimony/15 mL found for each of these sections by 1.708, a combination conversion and dilution factor (MW SbH 3/MW Sb) · (25 mL/15 mL). NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of stibine in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S243 was evaluated over the range 0.119 to 1.01 mg/m 3 using 20-L air samples [1]. Recovery averaged 98.6% in the range 0.12 to 1.0 µg SbH 3 per sample. The capacity of the sampling tubes (at a flow rate of 0.22 L/min, a SbH 3 concentration of 1.326 mg/m 3, and a relative humidity of 85%) was shown to be greater than 70 µg (as SbH 3). Previously, activated charcoal tubes were tried as a collection medium for stibine but were rejected because of poor collection efficiency [4].

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94