The effect of sodium chloride concentration, water content, and protein on the gas chromatographic headspace analysis of ethanol in plasma.

The authors used gas chromatographic headspace analysis to study the sodium chloride concentration dependence of the partitioning of acetonitrile, ethanol, n-propanol, and t-butanol from water and plasma to headspace vapor. Increasing the sodium chloride concentration caused logarithmic increases in the partitioning. At 25 degrees C the slopes (log10[peak height]/mol sodium/L) obtained with the use of water or plasma were as follows: acetonitrile, 0.064 (0.059); ethanol, 0.126 (0.125); n-propanol, 0.152 (0.149); and t-butanol, 0.200 (0.183). Differences in water content between the two liquids may contribute to the small differences in the regression data. More importantly, saturation with sodium chloride at 25 degrees C produced solutions with different sodium molarities: 5.2 mol/L for water and 4.8 mol/L for plasma. This difference in salt concentration at saturation and the volatile dependent slopes can account for a large part of the error in plasma ethanol concentrations when measured with the use of aqueous external standardization and internal standardization with any of the other volatiles. Deproteinization of the plasma abolished the liquid phase-dependent differences in saturated salt concentration and partitioning.

The effect of biologic specimen type on the gas chromatographic headspace analysis of ethanol and other volatile compounds.

Gas chromatographic analyses of 37 degrees C headspace vapors above liquid phases saturated with sodium chloride demonstrated that the partitioning of isopropanol, n-propanol, and t-butanol from blood, plasma, or serum to headspace vapor was greatly reduced relative to that observed with the use of water as the liquid phase. The partitioning of ethanol and acetone was moderately reduced with these specimens relative to water, while no effect was seen with methanol or acetonitrile. Normal urine only slightly affected relative partitioning, and vitreous humor had no effect. The partitioning reductions observed with blood were not affected by changing the equilibration temperature to 25 degrees C, by lengthening the equilibration time to three days, nor by changing the concentration of the volatiles in the liquid phase. The use of saturated sodium sulfate enhanced the differences in partitioning observed between water and blood. Only with substantial dilution (5:1) of blood specimens was the effect abolished.

Use of commercially prepared control sera as quality control materials for spectrophotometric bilirubin determinations in amniotic fluid.

The visible absorption spectra of dilutions of commercially prepared chemistry control sera closely mimic those of jaundiced amniotic fluids in cases of fetal rhesus isoimmunization. The authors have assessed the use of these materials for the quality control of net absorbance measurements at 450 nm on amniotic fluids. The authors conclude that they are excellent quality control materials because of their ready availability, low cost, long-term stability, wide range of bilirubin concentrations, and their close resemblance to jaundiced amniotic fluids with respect to light absorption and scattering, sensitivity to light, and pigment extractability into chloroform. Their spectra also contain a maximum at 410 nm, so these materials can also be used as controls for net absorbance measurements at 410 nm, a determination that indicates the extent of heme or meconium pigment interference with net absorbance measurements at 450 nm. These materials both supplement and complement the requisite spectrophotometric performance checks of wavelength calibration and photometric accuracy.