Page:NIOSH Manual of Analytical Methods - 7907.pdf/2

 VOLATILE ACIDS by Ion Chromatography: METHOD 7907, Issue 1, dated 20 May 2014 - Page 2 of 6

OTHER METHODS: This procedure, which is consistent with ISO 21438-2 [4], replaces NIOSH 7903 [7] for the determination of HCl, HBr and HNO3 in workplace air samples by IC. The main advantage of this method is that it provides for lower limits of detection and quantitation for volatile acids due to higher sampling flow rates. REAGENTS:

EQUIPMENT:

1.	Water, deionized (DI), ≥18 MΩ-cm resistivity 2.	Sodium carbonate (Na2CO3), anhydrous, American Chemical Society (ACS) analytical grade 3.	Sodium hydrogen carbonate (NaHCO3), ACS analytical grade 4.	Extraction & eluent stock solution: 0.62 M Na2CO3 / 0.069 M NaHCO3; Dissolve 13.14 g Na2CO3 and 1.15 g NaHCO3 in 50 mL of deionized water and swirl to mix. Then bring to 200 mL in a volumetric flask, stopper and mix thoroughly. 5.	Extraction and eluent solution; 0.0031 M Na2CO3/ 0.00035 M NaHCO3: transfer 10 mL 0.62 M Na2CO3 / 0.069 M NaHCO3 stock solution to a 2 liter volumetric flask, dilute to the mark with deionized water, stopper and mix thoroughly. 6.	Chloride (Cl-), bromide (Br -) and nitrate (NO3-) standard solutions, 1000 mg/L. 7.	Calibration stock solution, 100 µg/mL (as the anion): Transfer 10 mL aliquots of chloride, bromide and nitrate standard solution into a 100 mL volumetric flask, dilute to the mark with deionized water, stopper and mix thoroughly. 8.	Sodium carbonate solution, for impregnation of 37 mm diameter quartz fiber filters, 1 mol/L: dissolve 10.6 g Na2CO3 in deionized water, quantitatively transfer the solution into a 100 ml volumetric flask, dilute to the mark with deionized water, stopper and mix thoroughly. 9.	Preparation of the sampling filter: Apply 500 µL of the sodium carbonate solution, 1 mol/L, evenly on the 37 mm quartz fiber filter and allow to dry for 6 hours in a desiccator. (See NOTE 1, Step 1, p 7907-3.) Good for 14 days.

1.	Sampler: filter, 37-mm diameter quartz fiber impregnated with 500 µl 1 M Na2CO3; and pre-filter, 37-mm diameter quartz fiber filter separated by a spacer in a chemically inert cassette filter holder 2.	Spacers, of 37-mm diameter suitable for use with the samplers, manufactured from a chemically inert material, e.g. polypropylene sleeves 3.	Personal sampling pump, 1 to 5 L/min, with flexible connecting tubing 4.	Ion chromatograph (IC), with pre-column (50 mm by 4.0 mm), anion-exchange column (200 mm by 4.0 mm), suppressor column (4 mm) and conductivity detector; and connected to data processing unit 5.	Ultrasonic bath 6.	Vessels, 15-mL, plastic, with screw caps 7.	Volumetric flasks, 10- to 2000 mL 8.	Pipets, 10 to 5000 µL 9.	Beakers, 25 to 100 mL 10. Water purification system, to prepare ≥18 MΩ-cm resistivity deionized water 11.	Bottles, polyethylene, 100 mL 12. Syringes, plastic, 5 mL 13. Syringe filter cartridges, with 0.45-µm pore size polytetrafluoroethylene (PTFE) membrane filters 14.	Micro-syringes, 50 µL, with 60 mm x 0.6 mm needles 15.	Auto-sampler vials, with slotted septum, 2 mL capacity 16.	Analytical balance, with capability of weighing to nearest 0.01 mg


 * See Special Precautions

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition