Page:NIOSH Manual of Analytical Methods - 5525.pdf/5

 ISOCYANAT ES, TOTA L (MAP): METHO D 5525, Issue 1, dated 15 March 2003 - Page 5 of 17 CALIBRATION AND QUALITY CONTRO L: 7. Ca librate with six working standards in the range of interest. Prepare liquid standards with concentrations in terms of m oles isocyanate group per liter (normality) in the range 3 x 10 -5 N to 2 x 10- 8 N. Intersperse standards am ong sam ples. For filter samples and impingers, liquid standards should consist of the MAP derivative(s) of the app ropriate diisocyanate m onom er(s) in acetonitrile. A concentrated stock solution of the MAP derivatives of isocyanate monom ers can be made in methylene chloride. (Solubility: 1x10 -3N to 5x10 -3N). See AP PE NDIX C for synthe sis of M AP deriva tives to be used as standards. For filter samples only, to m imic sam ples in artifac t content, a MAP impregnated filter similar to the filter used for the sam ple ca n be place d in 5.0 mL of each level of standard, and then treated the same as the samples starting at step 4. 8. Prepare calibration graphs (response vs. no rm ality of stan dard solution) for both the UV and fluorescence dete ctors. a. The calibration curve prepared from either the UV or the FL detector may be used to quantify the m onom er. A quadratic fit may be used for the fluorescence calibration curve if curvature is seen at the low end. b. A linear calibration curve using UV peak area must be used to quantify the oligomer because the UV respon se fo r m ono m er an d oligom er is the sam e wh ile the FL res pon se is not. 9. Analyze two solvent blanks at the beginning of each sample set. Using the second blank chromatogram, subtract this chromatogram electronically from sam ple chromatograms. This improves the UV baseline of sample chromatograms and facilitates accurate integration of peaks in low level samples. Analyze one add itional so lvent blank within the sam ple se t. 10. Analyze a minimum of three field controls and three field blanks or at least one field control and one fie ld blank for every ten samples. Use the field controls and field blanks to identify non-isocyanate peaks (generally reagent artifact peaks) that are likely to appear in the samples. If the blanks are consistent and the sam ple set is analyzed soon after sampling, subtraction of a field blank instead of the solvent blank from the sam ple data m ay ma ke interpretation of the data simpler. 11. Analyze bulk isocyanate products whenever available, but if oligomer is to be quantified, analysis of the bulk products used at the worksite must be done. Bulk isocyanate chromatograms are useful for qualitative confirmation of p eaks observe d in the sam ple chro m atog ram s. It is also advisable to an alyze bulk non-isocyanate products (such as the polyol portion of a two-part spray system) in the same m anner to ensure that they give rise to no interfering com pounds that may be m istaken for isocyanates. Bulk prod ucts m ust be deriva tized with M AP prio r to analysis. A n appropriate dilution of the bulk in methylene chloride bas ed o n the m anu facturer’s NC O c onte nt, followed by imm ediate derivatization of an aliquot of this diluted bulk in 5 x 10-4 M MAP in aceton itrile m ust be done. After rea ctin g overnight, ac etyla te th is bulk-MAP rea ctio n m ixture with acetic anhydride as in step 4.b. AP PE NDIX D is a protoc ol fo r a b ulk dilution/derivatization with MAP that works well for most representative bulks. This bulk-MAP sample can then be analyzed on the HPLC. 12. Analyze three qu ality contro l blind sp ikes per s am ple se t.

MEASUREMENT: 13. Set HP LC and detectors to conditions an d se ttings g iven on pa ges 552 5-1 a nd 5 525 -2. Note th at in addition to a mobile phase flow of 1.5 mL/min, there is also a post column addition of 0.7 mL/min of 65:35 (v/v) ace tonitrile-4.4 N phos pho ric acid. Keep the column at constant temperature in an oven at 30 oC. Equilibrate the entire system for at least forty minutes before the sta rt of the daily analysis, us ing m obile phase B (65:35 (v/v) acetonitrile-pH 1.6 buffer), running post-column acid mobile phase also. 14. The HP LC grad ient pro gram can be custo m ized to optim ize the se para tion of the particular isoc yanate species. An example of a gradient program to start with is: 0 - 4 min: 100% m obile phase A (65:35 (v/v) acetonitrile-pH 6 b uffer) 4 - 17 min: Linear gradient from 100% mobile phase A to 100% mobile phase B (65:35 (v/v) acetonitrile-pH 1.6 bu ffer) 17 - 30 min: Hold 100% mobile phase B 30 - 36 min: Re-equilibrate at 100% m obile phase A NOTE 1: A gradient that provides better resolution for aliph atic isocyanate produ cts is given in Bello et al. [7].

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition