High-speed gas chromatographic analysis of solvents in pharmaceuticals using solid phase microextraction.

A simple, inexpensive and rapid analytical approach for the determination of organic volatile impurities in pharmaceutical drug substances is developed, where sample preparation step was conducted using solid phase microextraction (SPME), followed by a fast GC separation. With an extraction time between 3 and 5 min and separation of 13 solvents in less than 3 min employing fast temperature programming using resistively heated column, organic volatile impurities can be analyzed within a total analysis time of 6-9 min. Various SPME phases were evaluated towards sensitivity and selectivity for the extraction of 13 commonly found solvents in drug substances dissolved in dimethyl sulfoxide and water. A 2-cm Carboxen/polydimethyl siloxane/divinylbenzene (Carboxen/PDMS/DVB) phase and a 65-microm DVB/PDMS phase showed better sensitivity towards these solvents when extracted from organic and aqueous matrix in comparison with the sensitivity obtained with direct injection approach. Extraction parameters such as extraction time, extraction stir rate, etc. are discussed. %RSD of peak area of replicate extraction was between 2 and 10% when 100 microm PDMS was used for extracting solvents from aqueous matrix. When DVB/PDMS fiber was evaluated for precision, %RSD of peak area from replicate extractions of solvents from organic matrix was between 2 and 8%. One-hundred micrometer PDMS showed excellent linearity from 10 to 500 microg/ml for analytes extracted from water solutions. On the other hand, DVB/PDMS phase showed better linearity than Carboxen/PDMS/DVB fiber when it was used to extract analytes in the concentration range of 10-5000 microg/ml from organic matrix.

Evaluation of a magnetically coupled microcavity hollow cathode discharge for atomic emission spectroscopy.

A magnetically coupled microcavity hollow cathode discharge device was evaluated for its analytical potential as a boosted atomic emission source. A magnetic field using an electromagnet was applied perpendicular to the axis of the microcavity hollow cathode. The intensity of the atomic emission of copper, aluminum and the ionic emission of magnesium increased with increasing magnetic field until it reached a maximum. A further increase in the field strength did not lead to an enhancement of these emissions. The attainment of the maxima was attributed to the increase in the electron temperature and radial diffusion of the electrons from the center of the microcavity axis. Electron temperatures in the presence of the magnetic field calculated based on the semicorona model were shown to be proportional to the square of the reduced field strength. Further, these maxima were correlated to the energies of the upper levels of the transition studied.