BARIUM, soluble compounds: METHOD 7056, Issue 2, dated 15 August 1994 - Page 3 of 3 CALIBRATION AND QUALITY CONTROL: 11.
12. 13. 14. 15. 16.
Add known amounts of calibration stock solution to 10-mL volumetric flasks and dilute to volume with 5% HCl/1.1 mg/mL Na + solution to produce Ba 2+ concentrations in the range 0.4 to 40 µg/mL (0.002 to 0.2 mg per sample). Prepare fresh daily. Analyze working standards with the blanks and samples (steps 17 and 18). Prepare calibration graph (absorbance vs. solution concentration, µg/mL). Aspirate a standard for every ten samples to check instrument drift. Check recoveries with at least one spiked media blank per ten samples. Use method of standard additions occasionally to check for interferences.
MEASUREMENT: 17. 18.
Set spectrophotometer according to manufacturer's recommendations and to conditions on page 7056-1. Aspirate standards and samples. Record absorbance readings. NOTE: If absorbance values for samples are above the linear range of the standards, dilute with 5% HCl/1.1 mg/mL Na + solution, reanalyze, and apply the appropriate dilution factor in calculations.
CALCULATIONS: 19. 20.
Using the measured absorbances, calculate the corresponding concentrations (µg/mL) of barium in the sample, C s, and average media blank, C b, from the calibration graph. Using the solution volumes (mL) of the sample, V s, and media blanks, V b, calculate the concentration of barium, C (mg/m 3), in the volume of air sampled, V (L):
EVALUATION OF METHOD: Method S198 was validated using atomized aqueous solutions of barium chloride to generate atmospheres at approximately 0.3 to 1.1 mg/m 3 [1]. Samples taken at 1.4 L/min showed 100% collection efficiency. Recovery of barium chloride standards spiked on filters was 102% with Sr = 1.4% in the range 0.043 to 0.18 mg barium per sample.
REFERENCES: [1] Documentation of the NIOSH Validation Tests, S198, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-185 (1977), available as Stock No. PB 274-248 from NTIS, Springfield, VA 22161. [2] NIOSH Manual of Analytical Methods, 2nd ed., Vol. 3, S198, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-C (1977).
METHOD REVISED BY: Mary Ellen Cassinelli, NIOSH/DPSE.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
