Page:NIOSH Manual of Analytical Methods - 6016.pdf/3

 AMMONIA by IC: METHOD 6016, Issue 1, dated 15 May 1996 - Page 3 of 4 NOTE: Analyses should be completed within one day after the ammonia is desorbed. 7. Transfer samples to 10-mL syringes fitted with inline syringe filters for manual injection or transfer to autosampler vials. CALIBRATION AND QUALITY CONTROL: 8. Calibrate daily with at least six working standards over the range of 1 to 110 µg NH3 per sample (about 0.11 to 12 µg/mL NH4+). a. Add known aliquots of ammonia stock solution to 0.01 N H2SO4 in 10-mL volumetric flasks. NOTE: Prepare standards just before use. b. Analyze working standards together with samples and blanks (steps 9 through 11). c. Prepare calibration graph (peak height vs. µg NH3). MEASUREMENT: 9. Set ion chromatograph to conditions given on page 6016-1, according to manufacturer’s instructions. 10. Inject 50-µL sample aliquot manually or with autosampler. For manual operation, inject 2 to 3 mL of sample from filter/syringe to ensure complete rinse of sample loop. 11. Measure peak height. NOTE: If peak height exceeds linear calibration range, dilute with 0.01 N H2SO4, reanalyze and apply the appropriate dilution factor in calculations. CALCULATIONS: 12. Determine the mass, µg, of ammonia found in the sample front (W) f and back (Wb) sorbent sections, and in the average media blank front (B) f and back (Bb) sorbent sections. 13. Calculate concentration, C, of NH3 in the air volume sampled, V (L):

C

(W f

Wb

Bf V

Bb)

, mg/m 3

EVALUATION OF METHOD: This method combines the sampling procedure of NIOSH Methods S347 [4] and 6015 with the ion chromatographic analytical procedure of NIOSH Method 6701 [5] and OSHA Method ID-188 [3]. This method will serve as an alternate analytical procedure to the automated spectrophotometric procedure of method 6015. Although the methods from which this method is derived are fully evaluated methods, the combination of the sulfuric acid-treated silica gel sampler and IC analysis has not received a full evaluation as such. During the development of the passive monitor method for ammonia (6701), sulfuric acid-treated silica gel tubes were used as one of the reference methods [5]. The silica gel samples with IC analysis showed good agreement with the other reference methods, bubbler collection with colorimetric analysis using Nessler’s Reagent, and bubbler collection with IC analysis. A storage stability study compared the sulfuric acid-treated silica gel tube and sulfuric acid-treated carbon beads used in OSHA Method ID-188. When stored at room temperature for five days and then refrigerated for 21 days, silica gel samples had a mean recovery of 102 ± 3.8% (n = 8), while carbon beads had a mean recovery of 95 ± 1.6% (n = 8). The samples stored on carbon beads for 35 days showed significantly lower (although still acceptable) recovery compared to samples stored for 14 days: 103 ± 3.8% for silica gel (n = 12), and 108 ± 7.0% for carbon beads (n = 12) [2]. REFERENCES: [1]

NIOSH [1977]. Ammonia: Backup data report No. S347. Ten NIOSH analytical methods, set 6. SRI NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 5/15/96