A simple method using head-space gas for determination of blood alcohol by gas chromatography.

Abstract

A head-space gas chromatographic method for the determination of blood alcohol on a routine basis has been described and is simple, convenient, specific, and reliable. Samples and reference standards are prepared by placing 1 ml of blood in a serum bottle containing 20 mg of sodium fluoride and closed with a sleeve-type rubber cap. After reaching equilibrium in a thermostatically controlled water bath at slightly above room temperature, 1 ml of head gas is removed and injected into the gas chromatograph using a dual hydrogen flame detector. No internal standards are necessary. Reference standards are conveniently prepared from fresh bovine blood preserved with sodium fluoride and are stable as long as three months. The amount of blood sample placed in the vial before withdrawing the vapor is of little importance to the determination, and multiple withdrawals of head-space gas may be made. Salt concentration effects on small samples were eliminated by arranging the sample blood and the reference standards to contain at least 30 mg NaF/ml blood in the headspace vial. The most critical parameter of the procedure is the equilibrium temperature of the sample from which the head-gas is drawn. At slightly about room temperature a deviation of 1 deg C between standard and sample could result in a difference of apparent alcohol content of as much as 0.03 percent, and the effect of temperature variation is even greater at elevated temperatures. Other volatile compounds including alcohols can be differentiated from ethanol. Good precision is obtained, peak heights of standards are linear, and accuracy was proved by comparison with oxidation methods. The charts obtained are valuable records for court purposes.