CROTONALDEHYDE: METHOD 3516, Issue 1, dated 15 August 1994 - Page 3 of 4 SAMPLE PREPARATION: 8.
Remove bubbler stem and drain contents into bubbler flask. If necessary, bring to 10-mL mark with distilled water. Add 5 mL formate buffer solution and swirl bubbler to mix contents well.
CALIBRATION AND QUALITY CONTROL: 9.
10.
Prepare at least six working standards having concentrations to cover the range of 6 to 280 µg per sample (corresponding to 0.1 to 4 times the OSHA standard). a. Add appropriate aliquots ( ≤ 100 µL) of stock solution to 10 mL of hydroxylamine solution, followed by addition of 5 mL of formate buffer solution. b. Analyze with samples and blanks (step 11). c. Prepare calibration graph of peak current vs. mass (µg) of crotonaldehyde per 15 mL of sample. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph is in control.
MEASUREMENT: 11.
Transfer sample to electrochemical cell and purge with oxygen-free nitrogen for 3 min at 200 mL/min. Analyze by differential pulse polarography: 1 second drop time, 5 mV/second scan rate, and -0.6 V to -1.2 V scan range vs. a saturated calomel electrode (SCE). Analysis should be conducted in a relatively stable temperature environment. Measure peak current due to reduction of crotonaldehyde oxime. The half wave potential, E ½, of crotonaldehyde oxime is -1.03 V vs. SCE. Rinse electrodes before analyzing next sample.
CALCULATIONS: 12. 13.
Determine the mass, µg, for each sample (W) and for the average media blank (B) from the standard calibration graph. Calculate concentration, C, of crotonaldehyde in the air volume sampled, V (L), applying a correction for the collection efficiency, which was determined to be 96%:
EVALUATION OF METHOD: The average concentrations obtained from analysis of samples collected from test atmospheres at 0.5X, 1X, 2X, and 4X the OSHA standard were 10.0% lower, 2.1% lower, 3.7% higher, and 3% higher, respectively, than the "true" concentrations. The difference between the "found" and "true" concentrations may not represent a bias in the sampling and analytical method, but rather a random variation from the experimentally determined "true" concentration. Therefore, the method has no uncorrected bias. Storage stability studies on samples collected in a test atmosphere at a concentration of 5.80 mg/m 3 indicated that collected samples are stable for at least 7 days at 8 °C. Collection efficiency for the midget bubbler was determined to be 0.96 for an average of 24 samples and a correction must be applied. Statistical information [6] and details of the test procedures [1] can be found elsewhere.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
