UV spectrophotometric method for determination of phenacetin in biological specimens

Liquid chromatography in pharmaceutical analysis IX: Determination of muscle relaxant--analgesic mixtures using normal phase chromatography

High-pressure liquid chromatography was used to optimize the resolution of eight widely prescribed therapeutic agents commonly found in muscle relaxant--analgesic mixtures. The compounds were chromatographed on normal phase porpous silica or cyanopropylsilane columns, using various solvent systems paired on the basis of Synder's solvent selectivity scheme to give a polarity index for each system of 3.3. A carisoprodol, phenacetin, and caffeine mixture was selected to demonstrate the utility of the separation and quantification method. The mixture was chromatographed on a porous silica column, using tetrahydrofuran--toluene (50:50) at a flow rate of 2.0 ml/min. Each determination can be achieved in approximately 8 min with an accuracy of 3--5%.

GLC microanalyses of phenacetin and acetaminophen plasma levels

A GLC method utilizing a flame-ionization detector is described for the simultaneous analysis of acetaminophen and phenacetin in plasma. p-Bromoacetanilide is used as an internal standard. The drugs are extracted with ether from plasma diluted with 1 M phosphate buffer (pH 7.4). The ether extract is evaporated to dryness under nitrogen, and the residue is dissolved in 300 microliter of ethyl acetate. The ethyl acetate is transferred to a microcentrifuge tube (0.4 ml), and the sample is evaporated in a vacuum centrifuge. Then the residue is redissolved in 0.2 M trimethylanilinium hydroxide in methanol for GLC analysis. Extraction efficiency of added phenacetin and acetaminophen in plasma at concentrations of 1-10 microgram/ml was complete, and the limit of detection in plasma was less than 0.1 microgram.