IODINE: METHOD 6005, Issue 2, dated 15 August 1994 - Page 3 of 4 10. 11.
Agitate vials in ultrasonic bath for 2 min at room temperature. Draw sample extract through 13-mm PTFE filter attached to 3-mL syringe. NOTE: All samples, eluents and water flowing through the IC must be filtered to avoid plugging the system valves or columns.
CALIBRATION AND QUALITY CONTROL: 12.
13.
14.
Calibrate daily with at least six working standards. a. Add known aliquots of calibration stock solution to eluent in 50-mL volumetric flasks and dilute to the mark to prepare solutions containing 1 to 60 µg/mL of I¯ (equivalent to 1.2 to 72 µg/mL of I 2). Store in tightly-capped polyethylene bottles. Prepare fresh working standards weekly. b. Analyze working standards with samples and blanks (steps 15 through 17). c. Prepare calibration graph [peak height (mm or µS) vs. µg]. Determine desorption efficiency (DE) for each lot of charcoal used for sampling in the calibration range. Prepare at least three tubes at each of five levels. a. Place treated charcoal from unused front sorbent section in vial. Discard glass wool and backup section. b. Inject a known amount (2 to 5 µL) of DE stock solution, or a serial dilution thereof, onto charcoal with microliter syringe. c. Cap the vial. Allow to stand overnight. d. Desorb (steps 9 through 11) and analyze together with standards (steps 15 through 17). e. Prepare a graph of DE vs. µg I 2 recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 15. 16. 17.
Set ion chromatograph according to manufacturer's recommendations and to conditions given on page 6005-1. Inject sample aliquot. For manual operation, inject 1 to 2 mL of sample to ensure complete rinse of sample loop, or use autosampler. Measure peak height. NOTE: If sample peak height exceeds linear calibration range, dilute with eluent, reanalyze, and apply appropriate dilution factor in calculations.
CALCULATIONS: 18. 19.
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 iodine in the air volume sampled, V (L):
where 1.2 =
The stoichiometric factor arising from conversion of iodine to iodide on the sampler (3 I 2 + 6 OH¯ → 3 H 20 + 5 I¯ + IO ¯3).
EVALUATION OF METHOD: This method was optimized and evaluated by Southern Research Institute [1] and is based on a method developed by Kim et al. [5]. The method was evaluated over the range 0.74 to 2.11 mg/m 3 iodine in NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
