Quantitative analysis barbiturates

A number of methods have been reported recently for the gas chromatographic separation of nonderivatized "free" barbiturates. The method (35) below is applicable to the qualitative and quantitative analysis of barbiturates, glutethimide and Dilantin from serum. It is a simple, rapid but accurate procedure using only 3 cm of serum. Dilantin could be separated on the same column as the barbiturates after it had been converted to its methylated derivative. 

Barbiturates in either the free acid or salt forms are readily soluble in methanol and thus this is the solvent of choice for extraction in qualitative analysis. A known mass of the dose form is dissolved in a volume of methanol to provide the drug component at a working concentration of between 1 and 20 mgml The extract should be filtered or centrifuged prior to analysis in order to remove any unwanted particulate materials. For quantitative analysis, ethyl acetate can be used as the extraction solvent - if the drug is in the free acid form - with the extract treated in the same way as described above. If the original material is in the salt form, then the drug can be converted to the free acid form and extracted if required. 

The substance is dissolved in a 0.2 M alcoholic solution of trimethylanilinium hydroxide (1 5 w/v for the effect of concentration of the derivatizing agent upon the quantitation of barbiturates see Note and Ref. 22) and, after 2 min, the solution is injected into the gas chromatography for on-column reaction and GC analysis. 

The thermal decomposition of tetramethylammonium salts of barbiturates is a procedure used extensively for their methylation [512-515]. Decomposition is performed at 240°C (temperature of the injection port) with analysis on SE-30, QF-1 and similar stationary phases. The use of trimethylanilinium hydroxide leads to better reproducibility of the preparation of the phenobarbital derivatives and to an improvement in the quantitative results [516,517]. The disadvantage of this procedure is the dependence of the course of the reaction on several parameters, e.g., geometry of the injection port, temperature. 

Benzodiazepines may conveniently be extracted into methanol for both qualitative and quantitative analyses. The dose form should be triturated in methanol and as with barbiturates any solid material removed by centrifugation or filtration prior to analysis of the drug in solution. 

UV and visible absorption (also reflectance) microspectrometry has an extensive use in screening pigments and colors in paints, inks, and fibers, whereas it has found applications mostly for quantitative measurements in drug analysis (in particular for barbiturates). The development of sensitive IR spectrometers with Fourier transformation and... 

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