Page:NIOSH Manual of Analytical Methods - 5525.pdf/7

 ISOCYANAT ES, TOTA L (MAP): METHO D 5525, Issue 1, dated 15 March 2003 - Page 7 of 17 a. For impinger samples use the following formula:

whe re: M = N= W teq = Vf = Vt = V al =

m ass of isocyanate sp ecies (µg/sam ple), the normality (isocyanate milliequivalents per milliliter) of the analyzed sample solution as take n from the calibration curve, the equivalent weight of the m onomeric isocyanate in milligrams per isocyanate m illiequ ivalent, the final volum e of S PE solution in m illiliters, the 15-mL volume of the total sample, and the vo lum e of the aliquot analyzed.

b. For filter samples use the following formula:

where: M = N= W teq = Vf =

mass of isocyanate species (µg/sample) the normality (isocyanate m illiequ ivalents per milliliter) of the analyzed sam ple solution as taken from the calibration curve, the equivalent w eight of the monom eric isocyanate in milligrams per isocyanate milliequivalent, and the final volume of the sample solution in milliliters.

19. Oligom ers (total isocyanate): Identification of oligomers is best done by following the flow chart presented in Appendix E. T he bulk chrom atogram is used as the comparison standard when identifying which peaks to include in the quantification. Quantifica tion of oligomers m ust be acco m plished using a UV area calibration curve generated from analyzin g m onom er sta ndards, preferably using the m onom er on which the oligom er is based. Generate a calibration curve, plotting UV peak are a as a fun ctio n of concentratio n (n orm ality, isocyanate m illiequ ivalents per milliliter) of monom er standards. Use the slope of the linear portion of the calibration curve to determine the normality of a single compone nt, a gro up of c om ponents, or all isocyanate com pon ents in the analyzed sam ple aliqu ot.

where: N= UV = slopecal =

the norm ality of sam ple co m pon ent(s ), the UV area of sample component(s), and the slope of the calibra tion curve in units of U V area per norm ality.

The method m easures normality of oligomeric isocyanate group in the analyzed sample. It cannot m easure µg per sample unless the molecular weight of the component is known. Generally, there is a m ixture of compounds of different and unknown molecular weights. To deal in micrograms per sample, use the form ulae given above for m onom er quantification and the equivalent weight of the particular monom er of interest. This value is the monom er mass equivalent - the mass of the monom er that would conta in the same number of isocyanate groups as w as fou nd in the sam ple. Alte rnatively, the micrograms of isocyanate group per sample can be calculated using the formulae and entering 42 for the equivalent weight.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition