Page:NIOSH Manual of Analytical Methods - 5601.pdf/4

 ORGANONITROGEN PESTICIDES: METHOD 5601, Issue 1, dated 15 January 1998 - Page 4 of 21 calibration blank. b. Filter aliquots of standards and blanks for analysis (See Step 8). c. Analyze together with samples, blanks, and laboratory control samples (Steps 12 through 14). d. Prepare a calibration graph (ratio of peak area of analyte over peak area of internal standard vs. µg analyte). NOTE: Use of an internal standard is recommended [1,16], but optional if the precision of the injection device and HPLC system are known to be adequate. 11. Prepare desorption efficiency(DE) samples and Laboratory Control Samples (LCS) with each sample set at a rate of 10% of samples. a. Remove cap and the PTFE retainer ring from large end of sampler tube (to prevent wicking behind the ring). Apply known volume of calibration solution to face of quartz fiber filter. NOTE: Spike no more than 15 to 30 µL at a time. If more needs to be applied, connect the sampler to a vacuum pump with a flow 1 L/min, then apply spiking solution in 15- to 30-µL aliquots. Allow several minutes for the solvent to evaporate between each aliquot, to prevent wicking along the sides of the tube into the back-up section (5% or more may deposit on the walls of the tube). b. Cap and allow to stand a minimum of one hour. NOTE: Prepare LCS when samples arrive and store with field samples until analyzed. c. Include an unspiked sampler as a media (method) blank. d. Analyze with the field samples, blanks, and the liquid standards (Steps 12 through 14). MEASUREMENT: 12. Set liquid chromatograph according to manufacturer’s recommendations and to conditions listed in Table 3. Select two wavelengths for detection with 200 and 225 nm for general-purpose screens. For selected analytes, chose a more specific wavelength {from Table 10 or} from UV spectra where available. 13. Inject sample aliquot with autosampler. See Table 4 for approximate retention times of selected analytes. NOTE: If peak area is greater than the area of the highest standard, dilute with desorbing solution containing internal standards and reanalyze. Apply the appropriate dilution factor in calculations. 14. Measure peak area of analyte(s) and internal standard(s). Divide peak area of analyte by peak area of internal standard on same chromatogram. CALCULATIONS: 15. Determine the mass, µg, (corrected for DE) of analyte found in the sample filter and front sorbent section (Wf), back sorbent section (Wb), and the media blank front (Bf) and back (Bb) sorbent sections from a standard curve. 16. Calculate concentration, C (mg/m3), of each analyte in the air volume sampled, V (L).

C

NOTE: µg/mL

Wf

Wb

Bf V

Bb

, mg/m 3

mg/m3

CONFIRMATION: Retention Times with Alternate Conditions. Whenever the identity of an analyte is uncertain, confirmation may be achieved by analysis onan alternate column. If primary analysis was performed on a base-deactivated octadecylsilyl (C18) column, identity may confirmed by reanalysis on a cyanopropyl silica column, or by changing to a water/methanol mobile phase (see Table 9 for recommended alternative conditions). See Table 4 for approximate retention times for each column type and condition. Relative retention times (retention indices for a particular set of conditions) are more convenient for the identification of unknown analytes. NIOSH Manual of Analytical Methods, Fourth Edition