Page:NIOSH Manual of Analytical Methods - 5041.pdf/3

 Prepare three filters at each of five concentration levels plus three media blanks.


 * NOTE: Use separate filters for each analyte unless chromatographic conditions have been modified to permit baseline separation at concentrations >0.2 µg/mL (see APPLICABILITY and INTERFERENCES, Page 5041-1).
 * a. Place 13-mm glass fiber filters into 4-mL vials.
 * b. With a microliter syringe, fortify each filter with recovery solution.
 * c. Allow the uncapped vials to stand overnight at room temperature.
 * d. Prepare and analyze with working standards (steps 5 through 8, and steps 12 and 13).
 * e. Prepare graph of R vs. µg of analyte recovered.

11. Analyze three quality control blind spikes and three analyst spikes for each analyte to ensure that the respective calibration graphs are in control.

MEASUREMENT:

12. Set high performance liquid chromatograph according to manufacturer’s recommendations and to conditions given on page 5041-1. Inject 25-µL sample aliquot manually or with autosampler.
 * NOTE: If peak area is above the range of the working standards, dilute with acetonitrile, reanalyze, and apply appropriate dilution factor in calculations.

13. Measure peak area or height for each analyte.

CALCULATIONS:

14. Determine the mass, µg (corrected for R), of each analyte found on the filter (W) and the average media blank (B).

15. Calculate the concentration, C, of each analyte in the air volume sampled (L):

EVALUATION OF METHOD:

Average recoveries of capsaicin after fortification of 13-mm glass fiber filters with 0.13-, 0.28-, 0.58-, 1.1-, 2.9-, and 17-µg quantities of the compound were 1.02, 0.95, 0.98, 0.99, 1.04, and 1.00, respectively; precision (Š) was 0.042 (35 samples, pooled). After 28 days storage at 5 °C, the average recovery of 0.99-µg quantities of capsaicin from glass fiber filters was 0.96; Sr was 0.023 (6 samples). In addition, the average recovery of 0.99µg quantities of capsaicin from glass fiber filters after 28 days storage at room temperature was 0.92; Sr was 0.052 (6 samples). These data for stored samples suggest that recovery and precision of measurement are improved when samples are stored at the lower temperature. Empty glass vials were fortified with 0.90-µg quantities of capsaicin and stored uncapped for three days at room temperature. The average recovery from the vials was 0.98; thus, the vapor pressure of capsaicin at room temperature is insignificant.

A standard solution of capsaicin in acetonitrile at a concentration of 0.5 µg/mL was found to be stable during 9 weeks storage at 5 °C. The container was sealed tightly to prevent evaporation of solvent during refrigeration.

Average recoveries of dihydrocapsaicin after fortification of 13-mm glass fiber filters with 0.11-, 0.28-, 1.1-, and 3.0-µg quantities of the compound were 0.94, 1.03, 0.99, and 0.93, respectively; precision (Šr) was 0.065 (23 samples, pooled). After 26 days storage at 5 °C, the average recovery from glass fiber filters fortified with 0.88 µg of dihydrocapsaicin was 0.88; Sr was 0.047 (6 samples).

This method was not evaluated with controlled atmospheres in a laboratory. However, the method was employed for measurement of capsaicin and dihydrocapsaicin in air at a pickle pepper processing plant [1,11]. A curious phenomenon was the fact that in each of many of the samples the ratio of capsaicin to dihydrocapsaicin was less than 1:1. Generally, capsaicin is the capsaicinoid that occurs in Capsicum fruit in the greatest abundance [3].