SIFT-MS measurement of VOC distribution coefficients in human blood constituents and urine.

The new technique of selected ion flow tube-mass spectrometry (SIFT-MS) has been applied to the measurement of Henry's Law constants for the volatile organic chemicals o-xylene and trichloroethylene that both have low solubility in aqueous solvents. The method is validated by measurements in water at 298 K using the equilibrium partitioning in closed systems (EPICS) methodology in which the equilibrium headspace concentrations for the volatile organic compounds (VOCs) are measured in two sealed bottles containing different liquid volumes of very dilute solutions of the VOC. The range of solvents is then extended to human body fluids at 309 K including urine, saline, whole blood, red cells in saline, and plasma. The dimensionless distribution coefficients for these solvents vary markedly in the different fluids. For o-xylene they range from k(H) = 0.12-0.15 for water, saline, and urine; 0.53 for red cells in saline; 1.9 for whole blood; to 2.4 for plasma. For trichloroethylene the distribution coefficients range from k(H) = 0.070-0.091 for water, saline, and urine; 0.28 for red cells in saline; 0.35 for plasma; to 0.48 in whole blood. The very different solubilities of organic solvents in body fluids influence the uptake of solvents in workers exposed to VOCs. Some implications of these measurements are briefly discussed.

Reactions of CH3OCH2+ with hydrocarbons and O, N, and S compounds: applications for chemical ionization in selected ion flow tube studies.

We report the results of a flowing afterglow ion source-selected ion flow tube study (FA-SIFT) of the reactions of the methoxymethyl cation, CH3OCH2+. Rate coefficients and product branching ratios are reported for twenty nine reagent molecules including those that constitute the major ingredients of air, the hydrocarbons CH4, C2H6, C3H8, n-C4H10, C2H2, C2H4, C3H4 (allene and propyne), C6H6, and the S-containing molecules H2S, CH3SH, C2H5SH, (CH3)2SH, and (C2H5)2SH. In addition, we examined the reactions with the N-containing molecules NH3, CH3NH2, (CH3)2NH, (CH3)3N, pyrrole, pyridine as well as CH3COCH3. The results can be summarized under three general reaction types: Reaction at the CH3 carbon, reaction at the CH2 carbon, and association. The results also indicate that the methoxymethyl cation can be used as a chemical ionization source for the detection of trace levels of S-containing compounds in saturated hydrocarbons.

In situ analysis of solvents on breath and blood: a selected ion flow tube mass spectrometric study.

We report measurements of residual vapour levels of xylenes and trimethylbenzenes, present following a floor re-surfacing procedure, using the technique of selected ion flow tube mass spectrometry (SIFT-MS). A subject exposed to controlled amounts of xylene and mesitylene was monitored by direct breath exhalation over a 4-hour period after exposure to the volatile organic compounds (VOCs) had stopped. The headspace gases above 5 mL blood samples taken over this period were also monitored. The decays of the solvent levels with time were fitted to a two-compartment model with residence times for xylene and mesitylene of 0.37 h and 0.38 h, respectively (compartment one) and 2.5 h and 2.8 h, respectively (compartment two).