Page:NIOSH Manual of Analytical Methods - 5046.pdf/4

 TETRAKIS(HYDROXYMETHYL)PHOSPHONIUM CHLORIDE: METHOD 5046, Issue 1, dated 15 March 2003 - Page 4 of 5

aliquot of the remaining sample solution, reanalyze, and apply appropriate dilution factor in the calculations. 20. To ensure validity of the samples, identify those samples which contain more than 1000 µg of THPC per sample. The capacity of the samplers may have been exceeded for these samples, and collection of smaller samples would be warranted.

CALCULATIONS: 21. Determine m ass, :g, of THPC found on the fro nt filter, W F, on the backu p filter, W B, and on the average media blank, B, from the calibration graph. 22. Ca lculate concentration, C, of THPC in the air volume sam ple, V (L). This air concentration of THPC is uncorrected for form aldehyde gas pres ent at the sam pling site (if any).

NO TE : µg/L = m g/m 3 23. Ca lculate the air concentration or average air concentration for formaldehyde gas, C form, in m g/m 3 in sideby-side sam ples collected according to NM AM 2016 [2] (see steps 4 and 6 of N MA M 50 46). 24. Ca lculate the corrected concentration, C’, of THPC (corrected for the concentration of formaldehyde gas in the air). The value of 6.35 is found by dividing the molecular weight of THPC by the molecular weight of formaldehyde.

EVALUATION OF METHOD: THPC aerosol can be determined by measuring the formaldehyde which is released from THPC in the presence of DNPH and heat. However, formaldehyde gas, if present in the air, will be an interference in the measurem ent of T HP C. This method attempts to measure TH PC aerosol by correcting for the presence of formaldehyde gas in the air. Th e sam plers for form aldehyde gas used in NMAM 2016 [2] c onceptu ally would have frits or filters in the inlets to trap THPC aerosol and allow formaldehyde gas to pass through to the beds of DNPH -coated silica gel. However, since the necessity of the frit or filter has not been determined, use of frits or filters is optional. The degree of interference from THPC aerosol in measuring formaldehyde gas by NMAM 2016 has not been determined. This method has not been tested by air sampling for THPC aerosol or by air sam pling fo r form aldehyde gas in a T HP C aeros ol environm ent. This m ethod was evaluated using 37-mm DNPH -coated glass fiber filters in three-piece cassettes and aqueous tetrakis(hydroxymethyl)phosphonium chloride. Average recoveries of 8-, 14-, 20- and 31-µg quantities of THPC from 37-m m D NPH-coated glass fiber filters ranged from 87% to 104% (23 samples, pooled RSD = 5.85%) [1]. Samples of THPC on DNPH-coated filters were stable during storage at 5 oC in the dark; average recoveries of 15.0-µg quantities of THPC from DNPH -coated filters ranged from 108 % to 131% after 7 to 28 days of storage at 5 oC (n = 21 sam ples, RS D = 2.7% to 5.4% ) [1]. The limit of detection and lower limit of quantitation of THPC were 2 and 6.5 µg per filter, respectively. These limits were fou nd by least sq uares calculation s based on six DN PH -coated filters fortified with known quantities of THPC.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition