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The precision and sensitivity of head‐space GC can be improved by careful selection of the operating conditions: partitioning in the vapor phase can be promoted by altering the sample matrix; the ratio of the volumes of the gaseous and liquid phases, the sample temperature, the equilibration time, and the effect of sample mixing should also be considered. Most of the principles covered here can be applied to either manual headspace GC or to headspace GC utilizing an automated sampler.

An autosampler intended for liquid injection into a gas chromatograph was modified to serve as an automatic headspace sampler by replacing the syringe with a 100-microL gas-tight syringe and shortening the needle that normally enters the vials for sampling. Instead of the usual 1.0 to 1.5 mL of liquid sample, the vials contained 200 microL of liquid; the vapor above the liquid was injected into the gas chromatograph. Blood samples from California drivers were analyzed for ethanol by using the modified autosampler and the values were compared with those obtained by two other methods: the Smith modified version of the Widmark diffusion desiccation oxidation method (J Lab Clin Med 38: 762, 1951) and direct injection of diluted blood into the gas chromatograph. The correlation coefficient between the headspace method described in this paper and the titration method was 0.984; with direct injection, 0.997.

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