Microtechniques for the gas chromatographic determination of barbiturates in small blood samples

A method for the determination of therapeutic levels of barbituric acids in 25 microliter of whole blood is described. After extraction and controlled concentration of the extract to a volume of 5 microliter, the barbituric acids are N,N'-dimethylated using a microrefluxer. Of the total extract 20-100% is injected into the gas chromatograph. Low blanks, recoveries of 70--80% and peak ratios that are comparable to those in calibration experiments are obtained provided the detailed working instructions are followed strictly. In addition, barbiturates were determined (1 ng in 25 microliter blood) using column-switching devices and nitrogen-sensitive detection.