CALCIUM and compounds, as Ca: METHOD 7020, Issue 2, dated 15 August 1994 - Page 3 of 4 CALIBRATION AND QUALITY CONTROL: 13.
14. 15. 16. 17. 18.
Add known amounts, covering the range 0 to 500 µg Ca per sample, of calibration stock solution to 100-mL volumetric flasks containing 2 mL each of the 50 mg/mL Cs and La solutions and dilute to volume with 5% HCl. Analyze the working standards along with the samples and blanks (steps 19 and 20). Prepare a calibration graph of absorbance vs. solution concentration (µg/mL). Aspirate a standard for every 10 samples to check instrument drift. Check recoveries with at least one spiked media blank per 10 samples. Use method of additions occasionally to check for interferences.
MEASUREMENT: 19. 20.
Set spectrophotometer according to manufacturer's recommendations and to conditions on page 7020-1. Aspirate standards and samples. Record absorbance readings. NOTE: If the absorbance values for the samples are above the linear range of the standards, dilute the solutions with 5% HCl and an appropriate amount of the 50 mg/mL Cs and La solutions, reanalyze, and apply the appropriate dilution factor in the calculations.
CALCULATIONS: 21. 22.
Using the measured absorbances, calculate the corresponding concentrations (µg/mL) of calcium 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, C (mg/m 3), of calcium in the volume of air sampled, V (L):
EVALUATION OF METHOD: Method S205 [2] was issued on September 26, 1975, and validated over the range 2.6 to 10.2 mg/m 3 using an 85-L air sample by lab testing with spiked filters and generated atmospheres of CaO, verified by EDTA titration [1]. Collection efficiency of 1.00 was determined for the sampling device. Precision and accuracy data are given on page 7020-1. An additional check showed an estimated LOD of 1 µg Ca per sample [3].
REFERENCES: [1] Documentation of the NIOSH Validation Tests, S205, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-185 (1977). [2] V. 3, S205, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-C (1979). [3] User check, UBTL, NIOSH Seq. #3990-Q (unpublished, November 29, 1983). [4] Ibid, NIOSH Manual of Analytical Methods, 2nd ed., Vol. 5, P&CAM 173, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 79-141 (1979).
METHOD REVISED BY: Mark Millson, NIOSH/DPSE and R. DeLon Hull, Ph.D., NIOSH/DBBS; S205 originally validated under NIOSH Contract CDC-99-74-45. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
