Comparison of two gas-liquid chromatographic methods for the determination of nitrazepam in plasma

Nitrazepam in plasma was determined by gas-liquid chromatography with a nickel-63 electron-capture detector, unchanged by a direct method and also by a hydrolysis method. The extraction in the direct method was carried out with benzenedichloromethane (90:10) and in the hydrolysis method with diethyl ether. The hydrolysis was performed with 6 N sulphuric acid. The hydrolysis product was extracted with toluene-n-heptane-ethyl acetate (80:20:5) directly from acid. Thus the commonly used change in pH was omitted. Nitrazepam concentrations in plasma were determined in 10 healthy volunteers after two oral doses (5 and 10 mg); 0.5 ml of plasma was used for each determination and clonazepam, methylbromazepam and methylnitrazepam were used as internal standards. The recoveries of the methods are almost quantitative (greater than 96%). The two methods are clinically comparable. The high sensitivity and specificity make these methods useful in clinical determinations of nitrazepam in plasma. Advantages and disadvantages of both methods are discussed.