POLYNUCLEAR AROMATIC HYDROCARBONS by HPLC: METHOD 5506, Issue 3, dated 15 January 1998 - Page 4 of 9
13. Set HPLC according to manufacturer’s instructions, conditions on page 5506-1, and steps 14 and 15. 14. Inject sample aliquot (10 to 50 µL). Start mobile phase gradient: a. Linear gradient from 60% acetonitrile/40% deionized water to 100% acetonitrile at 1 mL/min over 20 min. b. Hold at 100% acetonitrile for 20 min. c. Linear gradient to initial condition, 5 min. 15. Measure peak areas for each analyte using the appropriate detector as specified in Table 1. NOTE 1: The order of elution for the PAHs appears in Table 4. NOTE 2: If peak area is above the calibration range, dilute with acetonitrile, reanalyze, and apply dilution factor in calculations. NOTE 3: If sample has many interferences, additional sample cleanup may be necessary.
CALCULATIONS: 16. Read the mass, µg (corrected for R or DE) of each analyte found on the filter (W) and front sorbent (Wf) and back sorbent (Wb) sections, and on the average media blank filter (B) and front sorbent (B f) and back sorbent (Bb) sections from the calibration graphs. 17. Calculate concentration, C (mg/m3), as the sum of the particulate concentration and the vapor concentration in the actual air volume sampled, V (L).
W
C
Wf
Wb
B V
Bf
Bb
, mg/m 3
mg/m3
NOTE 1:
µg/mL
NOTE 2:
Wf and Wb include analyte originally collected on the filter as particulate, then volatilized during sampling. This can be a significant fraction for many PAHs (e.g., anthracene, fluoranthene, fluorene, naphthalene, phenanthrene).
EVALUATION OF METHOD: The UV detector is used to analyze for some PAHs (see Table 1), and the remaining PAHs are analyzed by a fluorescent detector, which gave better sensitivity for some PAHs. The ranges of the limit of detection (LOD) and the limit of quantitation (LOQ) values for the 17 PAHs are reported in Table 4 [4]. The LOD and LOQ values varied because of differences in the detectors used and the concentrations of the standards. Therefore, it is important that the LOD and LOQ values be determined for each set of samples. The LOQs are the lower end of the analytical ranges. The upper end of the analytical ranges were not determined. This method was evaluated by means of a user check [5]. An independent laboratory prepared spiked filters and sorbent tubes for a recovery and desorption efficiency study (see Table 4). For the filters, except naphthalene, the recovery results were greater than or equal to 75%. Since naphthalene is fairly volatile under ambient conditions, this may account for the poor recovery results. For the sorbent tubes, only four of the 17 analytes had desorption efficiencies that were greater than or equal to 75%. During the user check, the sorbent tubes were extracted by adding 5 mL acetonitrile and were allowed to stand for 30 minutes with occasional swirling. In more recent quality control experiments, the desorption efficiencies were often better for some analytes (see Table 4) [4]. These results were achieved using an ultrasonic bath for 30 to 60 minutes. The results indicated the importance of preparing media spikes for recovery and desorption efficiency studies for each set of samples; moreover, the results reenforce this need when using new lots of media.
REFERENCES:
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
