Page:NIOSH Manual of Analytical Methods - 7903.pdf/3

 ACIDS, INORGANIC: METHOD 7903, Issue 2, dated 15 August 1994 - Page 3 of 6

NOTE:	Particulate salts of the volatile acids (HCl, HB, HF, and HNO3), if present in the air sample, will collect on the glass fiber filter plug. To estimate the concentration these salts, analyze the plug separately from the front sorbent section. 6.	Place backup sorbent section in separate centrifuge tube. Discard urethane plugs. 7.	Add 6 to 8 mL eluent to each centrifuge tube. Heat in boiling waterbath for 10 min. NOTE:	Eluent used for desorption should be from same batch as the eluent used in the chromatograph to avoid carbonate/bicarbonate peaks near F- and Cl-. 8.	Allow to cool, dilute to 10.0-mL volume with eluent. 9.	Cap the centrifuge tube and shake vigorously. 10.	Pour sample into 10-mL plastic syringe fitted with in-line filter. CALIBRATION AND QUALITY CONTROL:

IC

AL

11.	Calibrate daily with at least six working standards covering the range 0.001 to 0.3 mg of each anion per sample. a.	 Add known aliquots of calibration stock solution to eluent in 50-mL volumetric flasks and dilute to the mark. b.	 Store working standards in tightly-capped polyethylene bottles. Prepare fresh working standards weekly. c.	 Analyze working standards together with samples and blanks (steps 12 through 14). d.	 Prepare a calibration graph for each anion [peak height (mm or μS) vs. concentration (μg per sample)].

ST OR

MEASUREMENT:

12.	Set ion chromatograph to conditions given on page 7903-1, according to manufacturer’s instructions. 13.	Inject 50-μL sample aliquot. For manual operation, inject 2 to 3 mL of sample from filter/syringe to ensure complete rinse of sample loop. NOTE: All samples, eluents and water flowing through the IC must be filtered to avoid plugging system valves or columns. 14.	Measure peak height. NOTE:	If sample peak height exceeds linear calibration range, dilute with eluent, reanalyze and apply the appropriate dilution factor in calculations. CALCULATIONS:

H

15.	Determine the mass, μg, of anion found in the sample front (Wf ) and back (Wb) sorbent sections, and in the average media blank front (Bf ) and back (Bb) sorbent sections. 16.	Calculate concentration, C, of acid in the air volume sampled, V (L):

C=

((Wf + Wb ) − (Bf + Bb ))F V

, mg/m3

where: F (conversion factor from anion to acid) =	 1.053 for HF; 1.028 for HCl; 1.032 for H3PO4; 1.012 for HBr; 1.016 for HNO3; and 1.021 for H2SO4.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition