ALKALINE DUSTS: METHOD 7401, Issue 2, dated 15 August 1994 - Page 3 of 4 d. e. f.
9.
Remove electrodes, rinse them into the titration vessel, and bubble N of the titration vessel for 3 to 5 min to remove dissolved CO 2. Proceed with the titration to the inflection point. Calculate the normality of the stock HCl solution:
2
gas through contents
Standardize the working (ca. 0.01 N) NaOH solution against the standardized HCl solution by following steps 8.c. and 8.e, substituting the standardized HCl stock solution for the Na 2CO 3 solution and the 0.01 N NaOH solution for the 0.1 N HCl solution. Calculate the normality of the NaOH titrating solution. NNaOH = (N HCl)(mL HCl used)/(mL NaOH used)
10.
Prepare at least three spiked media blank samples to check analytical recoveries at levels expected on the field samples.
MEASUREMENT: 11. 12.
Back-titrate the excess HCl in the samples, blanks and spiked blank solutions with the standardized NaOH solution while maintaining the N 2 purge. Observe the pH meter. Calculate the endpoint (mL of 0.01 N NaOH used).
CALCULATIONS: 13.
Using the normality (N) and volumes of NaOH in the titration of the sample (V NaOH-s ) and average blank filter (V NaOH-b ), and the volume of air sampled, V(L), calculate the concentration, C (mg/m 3), of alkalinity (as NaOH with equivalent weight = 40.0):
EVALUATION OF METHOD: Method S381 [1] was issued on July 8, 1977, and was validated using generated atmospheres of NaOH over the range 0.76 to 3.9 mg/m 3 using a 360-L sample [1,6]. Overall precision, SˆrT, was 0.062 with an average recovery of 105%, representing an insignificant bias. The NaOH concentration was independently verified by analyzing additional samples for sodium by atomic absorption spectrophotometry. An overall average collection efficiency of greater than 99% was found by sampling 1 to 360 L in an atmosphere of 7.50 mg/m 3 (NaOH) using backup Fluoropore filters and also by collecting two 615-L samples using backup impingers filled with water.
REFERENCES: [1]
[2] [3]
Backup Data Report No. S381, Sodium Hydroxide, prepared under NIOSH Contract No. 210-76-0123, available as Order No. PB 275-838 from NTIS, Springfield, VA 22161 (July 8, 1977). NIOSH Manual of Analytical Methods, 2nd. ed., V. 4, S381, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-175 (1978). Ibid, V. 1, P&CAM 241, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-A (1977). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
