Page:NIOSH Manual of Analytical Methods - 2539.pdf/3

 ALDEHYDES, SCREENING: METHOD 2539, Issue 2, dated 15 August 1994 - Page 3 of 10 4. 5. 6. 7.

Score each sampler with a file in front of the first sorbent section. Break sampler at score line. Remove and place front glass wool plug and front sorbent sec tion in a via l. Tra nsfe r ba ck s ectio n w ith re ma ining glas s wo ol plu gs to a se con d via l. Add 1.0 m L tolu ene to ea ch v ial. C rim p ca p tigh tly on to ea ch v ial. Agitate vials in an ultrasonic bath for 60 min.

CALIBRATION AND QUALITY CONTROL: 8.

9.

Prepare qualitative oxazolidine standard samples. a. Prepare aldehyde standard stock solutions. NOTE: Alde hyd es c an o xidiz e to o ther com pou nds on e xpo sure to air. Th is will introduce bias into the method, so use of freshly-opened bottles of aldehydes is recommended. (1) Inject an aliquo t of form aldeh yde s tock so lution dire ctly onto the so rben t. (2) Take sp ecial care with ace taldehyde b ecause of its volatility. To prepa re acetaldehyde standard solutions, weigh a 10-mL capped volumetric flask containing about 5 mL toluene. With a cooled pipette, transfer about 1 mL of acetaldehyde into the weighed flask, recap and reweigh. Dilute to the mark. (3) For the other aldehydes, add measured aliquots (ca. 12 :L) of each to toluene in 10-mL volumetric flasks and dilute to the mark. From the density of each aldehyde, determine the amount of each aldehyde present in each solution (ca. 1 :g/:L). b. Inject 10 :L of the standard aldehyde solutions separately onto blank tubes from the same lot as the field samples. c. Analyze (steps 4 through 7 and 10 through 12) along with blanks for qualitative identification of derivative peaks by retention times. Determine limit of detection (LOD) for individual aldehydes by GC/FID with standards covering the range 0.5 to 10 :g per sam ple. Do this onc e, wh en first se tting up the m ethod to determine approximate sensitivities for the various aldehyde derivatives. Subsequently, analyze only low-level formaldehyde standard samples with each set of samples as an internal check that the analytical system is working. a. Weigh 120-m g portions of unused sorbent from media blanks into vials. Keep at least three 120-mg portions of this sorbent for determination of the background levels of each aldehyde. b. Add 0.5- to 10-:L aliq uots of the indiv idua l alde hyd e sta nda rd so lution s to o btain standard samples in the range 0.5 to 10 :g pe r 12 0 m g po rtion of so rbe nt. C ap v ials and allow to stand overnight at room temperature. c. Desorb the standard samples of aldehydes (steps 6 and 7) and analyze (steps 10 throu gh 12 ) along with bla nks. d. Determine lowest spike to be detected (peak area greater than three times the background or lowest standard observable) to estimate LOD for each aldehyde. NOTE: Because the working standards are prepared on media blanks, no additional blank correction or desorption efficiency correction is necessary.

MEASUREMENT: 10.

11.

Set gas chromatograph to manufacturer's recommendations and to conditions given on page 2539-1. Inject 1-:L sam ple aliqu ot. NOTE: If the am oun t of oxa zolidine in the a liquot ex ceed s the c apa city of the colum n, dilute the sample with toluene. Compare retention times of unknown peaks in samples to the retention times for the oxa zolid ines as d eter min ed b y the qua litative stan dar d sa mp les. (S ee A ppe ndix B for sam ple

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition