ALIPHATIC ALDEHYD ES: METHO D 2018, Issue 1, dated 15 March 2003 - page 4 of 10 9. Determine recoveries (R) of aldehydes from samplers in the calibration range (step 8). Prepare three sorbent beds at each of five concen tration levels for each aldehyde plus three m edia blanks. Re covery is exp ecte d to be near 100% for acetaldehyde, propionaldehyde, and valeraldehyde and about 86% for isovaleraldehyde. a. Prepare series of dilutions of fresh fortification stock solutions in the range of 50 to 300 µg/mL in 20m L vials (one dilution fo r eac h fortification level for eac h alde hyde). Cap vials tigh tly. Use acetaldehyde fortification solutions within 15 minutes of preparation or significant losses of acetaldehyde may occur. Use propionaldehyde, valeraldehyde and isovaleraldehyde fortification solutions within 30 m inutes of preparation (a limit of 30 minutes is preca utionary). b. Fortify beds of sorben t. Usin g a 100-µL syringe, measure 20 to 90 µL of the particular aldehyde solution. Penetrate the center of the frit at the inlet of the sampler with the needle of the syringe. Inject the solution into the cente r of the sorb ent bed. It is recom m end ed that each s am pler be fortified with only one injection of 90 µL of less. Injection of an exces sive volume of solution may lead to incom plete reaction of aldehyde with DNPH. c. Prepare the fortified sam ples (steps 7a an d 7b). d. Transfer 3-m L aliquots of sam ples to 4-m L vials a nd a nalyze togeth er with working standards (steps 11, 13 and 14 ). e. Prepare graph of peak height vs. concentration of aldehyde in µg/sample for each of the aldehydes. f. Ca lculate recovery (R) for each sample by dividing the quantity of aldehyde found in the sample by the quantity of aldehyde applied. g. Prepare g raphs of R vs. µg of aldehyde found (rec overed). 10. Fortify three quality control samples and three analyst samples with known quantities of free aldehyde and aldehyde-DNPH in separate experiments. Analyze these samples to ensure that the calibration and recovery graphs are in control.
MEASUREMENT: 11. Set the liquid chromatograph according to manufacturer’s recomm endations and to conditions given on page 2018-1 and in Table 1. 12. Transfer an aliquot of the sam ple solution from ste p 7.b. to a 4-m L vial. C ap the vial. 13. Injec t a 20-µL sam ple aliqu ot. 14. Mea sure peak height or peak area. If a sample peak is larger than the largest standard peak, dilute an aliquot of the rem aining sam ple so lution, reanalyze, and apply appropriate dilution factor in the calculations. 15. To ensure validity of the samples, identify those samples which contain more than 105, 183, 50 or 50 µg of acetaldehyde, propionaldehyde, valeraldehyde or isovaleraldehyde per sample, respectively. The cap acity of the samplers may have been exceeded for these samples, and collection of smaller samples would be warranted.
CALCULATIONS: 16. Determine m ass , µg, of aldehyde, W , foun d in the sam ple an d the average m edia blank , B, from the appropriate calibration graph. 17. Calculate conce ntration, C, of the aldehyde in the air volume sa m pled, V (L).
NO TE : :g/L = m g/m 3
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
