ISOCYANATES: METHOD 5522, Issue 2, dated 15 January 1998 - Page 3 of 6 b. Analyze together with samples, controls, and blanks (steps 10 through 12). c. Prepare calibration graph (response vs. µg per mL monomeric diisocyanate-tryptamine derivative). 9. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph is in control. MEASUREMENT: 10.
11.
12.
Set liquid chromatograph according tomanufacturer’s recommendations and to conditions given on page 5522-1. Inject 25-µL sample aliquot with a syringe, a fixed volume sample loop, or an autosampler. NOTE: Field sample run time = 60 min. To investigate any intrinsic fluorescence from the bulk components, add an aliquot of the bulk sample to 100% DMSO containing no tryptamine reagent and run a chromatogram (See Figure 1). NOTE: If the bulk sample is not soluble in DMSO, prepare a stock solution in an alternative solvent such as dichloromethane. Add aliquots of the stock solution to DMSO. Measure fluorescent response for all peaks in the chromatogram that also give an electrochemical response (See Figure 2). NOTE: If peak response is above the linear range of the working standards, dilute with sampling medium, reanalyze, and apply the appropriate dilution factors in the calculations.
CALCULATIONS: 13.
14.
Determine solution concentration (µg/mL) of each monomer derivative in the sample,sC , and average media blank, Wb, from calibration graph (step 8.c.). Sum the responses of all other confirmed peaks in the chromatogram that elute later than the monomer peak. Read solution concentration,s C (µg/mL), from calibration graph, and report as oligomer diisocyanate-tryptamine derivative. NOTE: Report the results for each monomer separately and the isocyanate-based oligomers as a group. Using the solution volumes (mL) of the samples, V s, and media blanks, Vb, calculate the concentration, C (mg/m3), of each monomer and oligomer in the volume of air sampled, V (L), applying the ratio of molecular weight of diisocyanate, MWDI (see Table 1), to the molecular weight of diisocyanatetryptamine derivative, MWDIT (see APPENDIX):
C
NOTE: µg/mL
(CsVs
CbVb) (MWDI / MWDIT) V
, mg/m 3
mg/m3
EVALUATION OF METHOD: During method development, the performance of the fluorescence detector was verified through the use of a second detector in series (an electrochemical detector). Recovery studies were conducted by analyzing groupsof five to six samples of each diisocyanate. Vapor spikes of 2,4-TDI, 2,6-TDI, and HDI were prepared. Because of the low vapor pressure of MDI, liquid spikes were prepared instead of vapor spikes. For 2,4-TDI, 3 concentrations ranging from 4.9 to 60 µg per sample yielded an average recovery of 90.5%. For 2,6-TDI, 3 concentrations ranging from 6.0 to 60 µg per sample yielded an average recovery of 102.8%. For HDI, 3 concentrations ranging from 5.0 to 47 µg per sample yielded an average recovery of 89.5%. For MDI, 3 concentrations ranging from 3.2 to 72 µg per sample yielded an average recovery of 96.4%. The recovery studies also were conducted in the presence of 17% water, since the DMSO solvent is known to be hygroscopic. The recoveries for 2,4-TDI, HDI, and MDI with 17% water present were measured at one concentration level with an average recovery of 94.5%. Storage stability studies were conducted at one concentration level by spiking groups of five to six impinger samplers with each diisocyanate-tryptamine derivative and storing at room temperature in the dark. Since NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
