Page:NIOSH Manual of Analytical Methods - 7401.pdf/2

 ALKALINE DUSTS: METHOD 7401, Issue 2, dated 15 August 1994 - Page 2 of 4 REAGENTS:

EQUIPMENT:

1. Sodium carbonate, primary standard grade. 2. Hydrochloric acid stock solution, 0.1 N. Standardize with sodium carbonate primary standard. 3. Dilute hydrochloric acid, 0.01 N. Dilute 10.0 mL 0.1 N stock HCl to 100 mL in a volumetric flask with distilled water. 4. Water, distilled, CO 2-free. Boil and cool under N2 or bubble nitrogen through distilled water for 30 min. Store with an Ascarite trap. 5. Nitrogen, compressed. 6. Sodium hydroxide, 50% w/v.* Dissolve 50 g NaOH in CO 2-free distilled water and dilute to 100 mL. 7. Stock sodium hydroxide, 0.1 N. Dilute 8 mL 50% NaOH to 1.0 L with CO 2-free distilled water. Store under Ascarite or other CO 2absorbing trap. 8. Working sodium hydroxide solution, 0.01 N. Dilute 10 mL stock (0.1 N NaOH) to 100 mL with CO 2-free distilled water. 9. Standard buffer solutions, pH 4 and 7.

1. Sampler: 37-mm diameter PTFE membrane filter (Millipore, Fluoropore or equivalent), 1.0µm pore size, supported by a cellulose backup pad in a cassette filter holder. 2. Personal sampling pump, 1 to 4 L/min, with flexible connecting tubing. 3. pH meter with pH electrode and recorder. 4. Titration vessel, 150 to 200 mL beaker, flask or jar with cover containing openings for the pH electrode and N 2 inlet and outlet. 5. Stirrer, magnetic, and stir bar. 6. Glass rod, ca. 5-mm diameter and 10 cm long to hold filter under liquid surface in titration vessel. 7. Pipets, 5- and 10-mL. 8. Volumetric flasks, 100-mL and 1-L. 9. Burets, 50-mL, readable to 0.1 mL. 10. Tweezers.


 * See Special Precautions

SPECIAL PRECAUTIONS: NaOH solutions are corrosive to tissue [4]. Handle with care. SAMPLING: 1. 2.

Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 4 L/min for a sample size of 70 to 1000 L. Do not exceed a filter loading of ca. 2 mg total dust.

SAMPLE PREPARATION: 3. 4. 5. 6.

Transfer the sample filter to a titration vessel with tweezers. Place the filter face down in the titration vessel. Place the end of a glass rod in the center of the filter to maintain the filter below the liquid surface during the analysis. Cover the titration vessel, add 5.00 mL 0.01 N HCl, start the magnetic stirrer and N 2 purge (ca. 0.1 L/min). Allow to stand 15 min (with stirring).

CALIBRATION AND QUALITY CONTROL: 7. 8.

Calibrate the pH meter with pH 4 and pH 7 buffer solutions. Standardize aliquots of the 0.1 N HCl stock solution with sodium carbonate in triplicate [3]. a. Dry 3 to 5 g primary standard grade Na 2CO 3 at 250 °C for 4 h. Cool in a desiccator. b. Weigh ca. 2.5 g Na 2CO 3 to the nearest mg. Dissolve and dilute to exactly 1 L with CO 2-free distilled water. The concentration is ca. 0.05 N Na 2CO 3. c. Place 5.00 mL 0.05 N Na 2CO 3 solution into a titration vessel and titrate potentiometrically to a pH of 5.

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