Page:NIOSH Manual of Analytical Methods - 2008.pdf/3

 CHLOROACETIC ACID: METHOD 2008, Issue 2, dated 15 August 1994 - Page 3 of 4 CALIBRATION AND QUALITY CONTROL: 10.

11.

12.

Calibrate daily with at least six working standards. a. Add known aliquots of calibration stock solution to deionized water in 10-mL volumetric flasks and dilute to the mark. Use serial dilutions as needed to obtain chloroacetic acid concentrations in the range 0.02 to 40 µg/mL. b. Analyze together with samples and blanks (steps 13 through 15). c. Prepare calibration graph [peak height (mm or µS) vs. µg chloroacetic acid per sample]. Determine desorption efficiency (DE) for each batch of silica gel used for sampling in the calibration range. Prepare at least three tubes at each of five levels. a. Place silica gel from unused front section in vial. b. Inject a known amount (2 to 20 µL) of calibration stock solution, or a serial dilution thereof, onto front sorbent section with a microliter syringe. c. Cap the vial. Allow to stand overnight. d. Desorb (steps 7 through 9) and analyze together with working standards (steps 13 through 15). e. Prepare graph of DE vs. µg chloroacetic acid recovered. Analyze three quality control spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.

MEASUREMENT: 13. 14.

15.

Set ion chromatograph according to manufacturer's recommendations and to conditions given on page 2008-1. Inject sample aliquot manually or use autosampler. a. Flush sample loop with 0.5 mL sample extract, then inject 0.5 mL sample. b. Rinse sample loop with 1 to 2 mL deionized water between determinations of separate samples. NOTE: All samples, eluents, and water flowing through the IC must be filtered to avoid plugging the system valves or columns. Measure peak height. NOTE: If sample peak height exceeds linear calibration range, dilute with deionized water, reanalyze, and apply appropriate dilution factor.

CALCULATIONS: 16. 17.

Determine mass, µg (corrected for DE), of analyte found in the sample front (W f) and back (W b) sorbent sections, and in the average media blank front (B f) and back (B b) sorbent sections. Calculate concentration, C, of chloroacetic acid in the air volume sampled, V (L):

EVALUATION OF METHOD: This method was developed and evaluated by Southern Research Institute [1] using dynamicallygenerated atmospheres of chloroacetic acid over the concentration range of 0.35 to 29 mg/m 3 at 25 to 27 °C and at relative humidity ≥80%. Average recovery based on 18 samples, six at each of three levels, was 98% representing a negligible bias. Precision at 0.35 mg/m 3 was inhomogeneous with those of higher levels; therefore, precisions were not pooled. Using this poorest precision (S r = 0.064), the overall precision ( SˆrT) was estimated to be ≤0.081.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94