Page:NIOSH Manual of Analytical Methods - 7907.pdf/3

 VOLATILE ACIDS by Ion Chromatography: METHOD 7907, Issue 1, dated 20 May 2014 - Page 3 of 6

SPECIAL PRECAUTIONS: Wear gloves, lab coat, and safety glasses while handling acids. All work should be performed with adequate ventilation for personnel and equipment. It is imperative that acid be added to water in order to avoid a violent exothermic reaction. Avoid direct contact since acids are both corrosive and irritants to eyes, skin, and the respiratory system [8,9]. SAMPLING, SAMPLE TRANSPORT AND STORAGE: 1.	Prior to sampling, load each clean sampler, first with a sampling (impregnated) filter, then with a prefilter, separating the filters with a spacer. Ensure that the configuration in which the filters are loaded leads to the sampled air passing first through the pre-filter and then through the sampling filter. Note 1:	 Three-piece polystyrene cassettes are appropriate, with the middle ring section of the cassette acting as the spacer. Impregnated filters that are stored in a desiccator can be prepared up to 14 days prior to their use for sampling. Note 2:	 Silica gel sorbent tubes [7] can be used in lieu of impregnated filters, but each sorbent tube must be preceded by a pre-filter. 2.	Calibrate each personal sampling pump with a representative sampler in the line. 3.	Sample accurately at 2 L/min for a total sample size of 30 to 500 L. Avoid sampler overloading [6]. 4.	Transport the samples to the laboratory in a manner that prevents contamination or damage to the filters. 5.	Submit at least three blank impregnated filters as field blanks for each set of samples collected per day. Handle these in the same way as the field samples. 6.	Ship all samples to the laboratory in accordance with established chain-of-custody procedures [10]. 7.	The samples can be stored at room temperature for one week; for longer storage, refrigerate the samples (4 °C). 8.	Analyze samples between 4 days and 4 weeks of sample collection. SAMPLE PREPARATION: 9.	Prior to carrying out sample dissolution, store the sampling filter for at least four days (to avoid nitric acid losses). 10.	Remove sample cassettes from storage and bring them to room temperature. Discard the pre-filters. NOTE:	If desired, the pre-filters can be analyzed for determination of particulate chlorides, bromides and nitrates. If this analysis is carried out, it is recommended to rinse the inside surfaces of the sampler with a few mL of DI water so as to include wall deposits along with material collected on the prefilter. 11.	Place the sampling filters (i.e., impregnated filter samples) in 15-mL plastic screw-cap vessels and add 10 mL of deionzied water to each sample. Securely cap the vessels. 12.	Sonicate the samples in an ultrasonic bath for at least 15 minutes, and allow to cool for approx. 30 minutes. 13.	Using 5-mL syringes, filter 5-mL aliquots of each sample extract solution through a PTFE filter into clean auto-sampler vials. CALIBRATION AND QUALITY CONTROL: 14.	With dilution of the calibration stock solution in eluent solution, prepare calibration working standard solutions covering the range of approximately 0.4 to 4 mg/L of chloride, bromide and nitrate. Store working standards in tightly sealed polyethylene bottles. Prepare fresh working standards weekly. 15.	Calibrate the ion chromatograph with at least six working standards covering the range of 0.4 to 4 mg/L of chloride, bromide and nitrate per sample by preparing a calibration graph of anion peak height (mm or µS [micro-siemens]) vs. concentration (mg/L).

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition