Page:NIOSH Manual of Analytical Methods - 7906.pdf/3

PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 3 of 6

SPECIAL PRECAUTIONS: Acids, particularly HF, are extremely corrosive to skin, eyes, and mucous membranes. HF will attack glass. Plastic labware is recommended. 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 [11,12]. 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. 2. Calibrate each personal sampling pump with a representative sampler in the line. 3. Sample at an accurately known flow rate between 1 to 2 mL/min for a total sample size of 15 to 1000 L. Avoid sampler overloading. 4. After sampling, remove the filters from the cassette and place them in screw-cap plastic vessels. For the pre-filter portion: With approximately 2 mL eluent(extraction) solution, rinse material from the inside surfaces of the pre-filter portion of the cassette into the vessel. Add eluent solution into the vessels until a final volume of 10 mL is reached. 5. Submit at least three blank untreated filters and 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; i.e., place each filter into a vessel, add 10 mL of eluent solution and ship it to the lab along with the remaining samples. 6. Refrigerate all samples that are to be stored overnight (or longer) prior to shipment to the laboratory. Ship all samples to the laboratory in accordance with established chain-of-custody procedures [13]. 7. Refrigerate the samples immediately upon receipt at the lab until ready for analysis. 8. Analyze samples within 2 weeks of receipt. The samples can be stored at room temperature for one week; for longer storage, refrigerate the samples (4 °C). SAMPLE PREPARATION AND MEASUREMENT: 9. Remove sample vessels from storage and bring them to room temperature. 10. Sonicate the samples in an ultrasonic bath for at least 15 minutes and allow to cool for at least 30 minutes. 11. Using 5- or 10-mL syringes, filter each sample extract solution through a PTFE filter and a styrenebased sulfonic acid resin cartridge (follow the manufacturer’s instructions), discard the first two milliliters and place the remaining solution in clean plastic vessels. CALIBRATION AND QUALITY CONTROL: 12. With dilution of the calibration stock solution in eluent solution, prepare calibration working standard solutions covering the range of approximately 0.4 to 8 µg/mL of fluoride. Store working standards in tightly sealed polyethylene bottles. Prepare fresh working standards biweekly. 13. Calibrate the ion chromatograph with at least six working standards covering the range of (at least) 0.4 to 8 µg/mL of fluoride per sample by preparing a calibration graph of anion peak height (mm or µS) vs. concentration (µg/mL). 14. Analyze working standards together with samples, reagent blanks and field blanks at a frequency of at least 1 per 20 samples (3 minimum of each). Cellulose nitrate filters demonstrate variable batchdependent blank values, thus media blank correction is essential.

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition