2,4-D AND 2,4,5-T: METHOD 5001, Issue 2, dated 15 August 1994 - Page 3 of 4 SAMPLE PREPARATION: 4. 5. 6.
Remove the filter from the cassette with clean tweezers and place it in a 20-mL vial. Add 15 mL methanol and mix by swirling. Allow to stand at least 30 min. Filter the sample. a. Pour the sample solution into a 20-mL syringe which is fitted with a 5-µm PTFE filter. b. Filter the sample into a clean vial. c. Clean the PTFE filter by backflushing with methanol. Rinse the syringe and plunger with methanol. Dry with air or nitrogen.
CALIBRATION AND QUALITY CONTROL: 7.
8.
Calibrate daily with at least five working standards. a. Dilute aliquots of calibration stock solution to 10 mL with methanol in volumetric flasks. b. Analyze working standards (steps 9 and 10). c. Prepare calibration graph (peak area vs. mg 2,4-D or mg 2,4,5-T). Check recovery with at least four spiked media blanks at each of four levels. a. Add aliquot of recovery stock solution to media blank. b. Analyze using standards prepared from the recovery stock solution. c. Calculate R (mg recovered/mg added).
MEASUREMENT: 9. 10.
Establish chromatographic conditions listed on page 5001-1 for either 2,4-D or 2,4,5-T. Inject 50 µL of sample in duplicate. Rinse and dry the syringe between samples. NOTE 1: The analyte is the chlorinated phenoxyacetate, whether the air sample contained salts or free acid forms of 2,4-D and 2,4,5-T. NOTE 2: Esters of 2,4-D and 2,4,5-T will not elute from the HPLC column and may, if present in large amounts, degrade the HPLC column. Protect the main column with a precolumn of Zipax SAX if esters are known to be present. The sample preparation conditions are sufficiently mild so as to preclude hydrolysis of the esters.
CALCULATIONS: 11. 12.
Read the mass of analyte, mg (corrected for recovery), in the sample (W) and average media blank (B) from the calibration curve. Calculate the concentration, C (mg/m 3), of 2,4-D or 2,4,5-T in air volume, V (L), taken:
EVALUATION OF METHOD: Methods S279 (2,4-D) and S303 (2,4,5-T) were issued on February 17, 1978, and March 17, 1978, respectively [3], and validated using 100-L air samples [1,2,5]. Atmospheres were generated using 2,4-D dimethylamine salt for S279 and Weedar Amine BK (Amchem; equal parts of 2,4-D dimethylamine salt and 2,4,5-T triethylamine salt) for S303. Overall precision and recovery for 100-L samples were as shown, representing non-significant bias in each method:
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
