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
    VOLATILE ACIDS by Ion Chromatography: METHOD 7907, Issue 1, dated 20 May 2014 - Page 4 of 6
16. 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).
    MEASUREMENT:
17. Set the ion chromatograph to recommended eluent flow rate (e.g., 1.5 mL/min) and recommended
    pressure ( e.g., 1.1 x 105
    kPa), and other conditions as specified by the instrument manufacturer.
18. Inject a sample aliquot, e.g., 25-µL, into the chromatograph, and measure the peak heights of
    the chloride, bromide and nitrate peaks (at retention times of approx. 5 min, 9 min and 12 min,
    respectively). If the peak height exceeds the linear calibration range, dilute with eluent, reanalyze
    and apply the appropriate dilution factor in calculations.
    CALCULATIONS:
19. Calculate the mass concentration of each anion, C (mg/m3
    ), in the air volume sampled, V (L):
    C C V F C V
    V
    F d = c − {
    ( ) ( )} * 1* 1 0 * 0*
    where:
    C0
    =mean concentration, in mg/L, of anion in the field blank test solutions;
    C1
    =concentration, in mg/L, of anion in the sample test solution;
    V = volume, in liters, of the air sample;
    V0
    = volume, in mL, of the field blank test solutions;
    V1
    = volume, in mL, of the sample test solutions
    Fd
    = dilution factor for each sample test solution
    Fc
    = conversion factor to convert from anion to acid concentration
    Fc
    = 1.0284 for chloride, 1.0126 for bromide, and 1.0163 for nitrate

Sample Solution