Page:NIOSH Manual of Analytical Methods - 5006.pdf/3

 CARBARYL: METHOD 5006, Issue 2, dated 15 August 1994 - Page 3 of 4 NOTE 1: The color degrades steadily with time. All samples, blanks, recovery spikes, and working standards must have exactly the same time for color development. NOTE 2: The PTFE in-line filter removes glass fibers from the samples. (Standards do not have to be filtered.) CALIBRATION AND QUALITY CONTROL: 10. Calibrate with at least six working standards over the range 0.05 to 1.0 mg Carbaryl per sample. a. Add known amounts of calibration stock solution to methanolic 0.1 M KOH in vials to make 20 mL of solution. b. After 5 min, transfer 2.0 mL of each solution into a clean vial. c. Prepare as in steps 7 through 9. d. Analyze together with samples and blanks (steps 13 through 15). e. Prepare calibration graph (absorbance vs. mg Carbaryl). 11. Check recovery with at least three spiked media blanks per sample set. a. Add aliquot of calibration stock solution with a microliter syringe directly to a representative filter. Air dry. b. Prepare and analyze together with working standards (steps 4 through 9 and 13 through 15). c. Calculate recovery [(mg recovered - mg blank)/mg added]. 12. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph is in control.

MEASUREMENT: 13. Set spectrophotometer at 475 nm. 14. Adjust baseline to zero with distilled water in both cells. 15. Read the absorbance of the sample against the absorbance of the reagent blank. NOTE 1: Prepare a fresh reagent blank with each small group of samples. The absorbance of reagent blanks increases with time [5]. NOTE 2: If absorbance of the sample is >1.0, dilute the filter extract (step 4) with methanolic 0.1 M KOH, reanalyze, and apply the appropriate dilution factor in calculations.

CALCULATIONS: 16. Determine the mass, mg of Carbaryl found on the filter, W, and average media blank, B, from the calibration graph. 17. Calculate the concentration, C (mg/m 3), of Carbaryl in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S273 [2] was issued on February 27, 1976, and validated over the range of 1.96 to 13.4 mg/m at 24 °C and 763 mm Hg [1]. Overall precision, SˆrT, was 0.057 with an average recovery of 102%, representing a non-significant bias. The concentration of Carbaryl was independently verified by a Thermo Systems particle mass monitor. Generated atmospheres were produced by nebulization of a toluene solution of a commercial formulation of Sevin containing 15% Carbaryl by weight. No Carbaryl was detected in bubblers (containing 0.1 M KOH in methanol) placed behind the glass fiber filters when 90-L air samples were taken of an atmosphere containing 15 mg/m 3 Carbaryl. Thus, it was concluded that Carbaryl vapor was not a significant factor. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94

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