Page:NIOSH Manual of Analytical Methods - 5046.pdf/3

 TETRAKIS(HYDROXYMETHYL)PHOSPHONIUM CHLORIDE: METHOD 5046, Issue 1, dated 15 March 2003 - Page 3 of 5

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In a similar fashion, prepare DNPH-coated silica gel samples for air sampling of formaldehyde gas [2]. NOTE: A frit or filter can be added in the inlet to trap T HP C aeros ol and sep arate the THPC from the formaldehyde gas. However, since the necessity of the frit or filter ha s not been dete rm ined, its use is option al. 5. Sample 1 to 480 liters of air at 1.0 to 1.7 L/min for THPC. 6. Conduct side-by-side air sampling for formaldehyde gas for the same period of time. Sample at 0.5 to 1.5 L/m in for fo rm aldehyde gas by NM AM 201 6 [2]. 7. Re place inlet ca sse tte piec e on the T HP C sam pler. Cap the outlet of the T HP C sam pler. Protect THPC sam ples from hea t. 8. Place end caps onto the formaldehyde sampler and seal sam pler in an envelope. Protect formaldehyde sam ples from hea t. 9. Ship THPC and formaldehyde samples in separate containers on ice (0 oC).

SAMPLE PREPARATION: 10. Fo ld the front and back DN PH-c oated filters using 2 pairs of forcep s and place into sepa rate 4-m L vials. Avo id finge r con tact. 11. Ad d 4.00 m L of carbonyl-free aceton itrile to each vial. C ap the vials tightly. 12. Place vials in water bath at 60 oC fo r 1 ho ur. 13. Rem ove vials from water bath and allow to cool to room tem perature. 14. Filter the sample solutions with syringe filters. Collect filtrates in separate autosampler vials. Cap the autosampler vials. NO TE : Follow NM AM 201 6, Issue 2, for the ana lysis of form aldehyde gas sam ples [2].

CALIBRATION AND QUALITY CONTRO L: 15. Ca librate daily with at leas t six wo rking (m edia) stan dard s over the rang e of interes t. a. Prepare a series of aqueo us TH PC s olutions for fortification of blank D NPH -coated filters (media blanks) by dilution of THPC fortification stock solution (item 6) with DI water. Suggested concentrations of THPC in solution include 400 and 800 µg/m L. M edia blanks and coated filters for actual air sampling should be from the same lot and should be handled and stored in the same m anner. b. Place folded filters in 4-mL vials and fortify with known quantities of THPC solution in the range of 20 to 80 µL. c. Prepare the m edia standard s (steps 11-1 4) an d an alyze (ste ps 1 7-19 ). d. Prepare a calibration graph (pe ak area or height vs. µg TH PC p er sam ple). 16. Determine percent yield of formaldehyde from TH PC in the calibration range (step 15) at least once. a. Ca lculate the concentration of formaldehyde-DNPH derivative in the calibration stock solution (about 1000 µg/m L). Calculate the equivalent concentration of free formaldehyde in solution by multiplying the derivative concentration by 0.143 (molecular weight of formaldehyde divided by the molecula r weight of form aldhyde-DNP H). b. Prepare a series of dilutions [working standards (liquid standards)] from 0.02 to about 1 µg/mL. c. Prepare six samples at the same level by fortifying six DNPH -coated filters with a known quantity of TH PC (step 15). d. Analyze sam ples (steps 17-19 ). e. Calculate the molar quantity of formaldehyde found in each sample. f. Calculate the m olar quantity of TH PC a pplied to each DN PH-c oated filter. g. Consider that one mole of THPC releases one mole of form aldehyde in the presence of DNPH. Calculate the percen t yield of form aldehyde (yield should be 100 %).

MEASUREMENT: 17. Set the liquid chro m atog raph acc ording to manufacturer’s recomm endations and to conditions given on page 5046-1. 18. Inject a 20-µL aliquot of filtered sample solution. 19. Mea sure peak height or peak area. If sample peak is larger than the largest standard peak, dilute an NIOSH Manual of Analytical Methods (NMAM), Fourth Edition