John H. Block

Use of flow programming in paired-ion high-performance liquid chromatographic analysis of dosage forms containing dyphylline

The use of paired-ion high-performance liquid chromatography (HPLC) for analyzing dosage forms containing dyphylline alone and in combination with other products is described. Liquid dosage forms were diluted and then injected without further treatment. Tablets required a simple extraction using the mobile phase or, in some cases, a modified mobile phase. Flow programming was utilized to hasten the analysis time for those products containing ephedrine and phenobarbital. Chromatographic conditions included a mobile phase consisting of 20 parts acetonitrile and 80 parts water which contained 4 · 10−3M octyl sodium sulfate and 1 % acetic acid. The flow-rate was 2 ml/min for the first 4.5 min and then 5 ml/min for the remaining 5 min. Sodium barbital was the internal standard. This procedure permitted the analysis of dyphylline, guaifenesin, ephedrine and phenobarbital. The HPLC results for dyphylline were compared with results obtained by ultraviolet spectrophotometry. There was no interference from dyes or preservatives.

Evaluation of descriptors and classification schemes to predict cytochrome substrates in terms of chemical information

Using a small database of defined substrates in humans for cytochrome P450 mixed function oxidases, a series of descriptors and classification methods were evaluated with respect to how well they correctly classified substrates. The descriptors ranged from structural keys to topological to electronic. A variety of classification schemes were examined in terms of their ability to point out which descriptors are important for predicting the cytochrome P450 specificity for a substrate. Results illustrate the relative effectiveness of the various kinds of descriptors and classification methods, as well as the value of using as well-defined data set as possible.