Controlled-pH tissue cleanup protocol for signal enhancement of small molecule drugs analyzed by MALDI-MS imaging.

The limit of detection of low-molecular weight compounds in tissue sections, analyzed by matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), was significantly improved by employing sample washing using a pH-controlled buffer solution. The pH of the washing solutions were set at values whereby the target analytes would have low solubility. Washing the tissue sections in the buffered solution resulted in removal of endogenous soluble ionization-suppressing compounds and salts, while the target compound remained in situ with minor or no delocalization during the buffered washing procedure. Two pharmaceutical compounds (cimetidine and imipramine) and one new protease inhibitor compound were successfully used to evaluate the feasibility of the pH-controlled tissue washing protocol for MALDI-MSI. Enhancement in signal-to-noise ratio was achieved by a factor of up to 10.

Unexpected products and reaction mechanisms of the aqueous chlorination of cimetidine.

Many pharmaceuticals and personal care products (PPCPs) resist degradation in wastewater treatment plants. Thus, they may be transformed by chemical disinfectants in the final treatment stage, generating products that may possess enhanced toxicity/biological activity relative to the parent compounds. For this reason, the reaction of cimetidine, an over-the-counter antacid, with the frequently used disinfectant, free chlorine, was investigated. Cimetidine degraded rapidly in the presence of excess free chlorine, indicating that it will likely undergo significant transformation during wastewater disinfection. Four major products were isolated and extensively characterized by comparison of liquid chromatographic retention times to known standards, mass spectrometry, 1H- and 2D-nuclear magnetic resonance spectroscopy, and infrared spectroscopy. An expected sulfur oxidation product, cimetidine sulfoxide, was identified along with three unexpected products: 4-hydroxymethyl-5-methyl-1H-imidazole, 4-chloro-5-methyl-1H-imidazole, and a product proposed to be either a beta- or delta-sultam. The last three products are formed by transformations not frequently observed in free chlorine reactions of PPCPs such as C-C bond cleavage and intramolecular nucleophilic substitution. The unexpected transformations yielded compounds with more substantial structural changes than would be observed in common free chlorine reactions such as N-chlorination or electrophilic halogenation. The reaction pathway was elucidated by kinetic analysis and by independently treating isolated intermediates with free chlorine, and reaction mechanisms were proposed. Finally, the predicted no-effect concentration (PNEC) of the chlorination products was estimated, and the products 4-hydroxymethyl-5-methyl-1H-imidazole and 4-chloro-5-methyl-1H-imidazole were estimated to have lower PNECs than cimetidine.

Liquid-phase microextraction based on carrier mediated transport combined with liquid chromatography-mass spectrometry. New concept for the determination of polar drugs in a single drop of human plasma.

Recently, we demonstrated for the first time liquid-phase microextraction (LPME) of polar drugs based on carrier mediated transport. In this new extraction technique, selected analytes were extracted as ion-pairs from small volumes of biological samples, through a thin layer of a water immiscible organic solvent immobilised in the pores of a porous hollow fibre (liquid membrane), and into a microl volume of an acidic aqueous acceptor solution placed inside the lumen of the hollow fibre. In the current paper, this new extraction technique was combined with liquid chromatography-mass spectrometry (LC-MS) for the first time. Carrier mediated LPME was evaluated for several new model drugs (0.01

Chemical and analytical characterization of related organic impurities in drugs.

A system is proposed for the classification of related organic impurities in drugs and drug products including among others (separated and non-separated) intermediates, various kinds of by-products, among them products of different side reactions, epimeric/diastereomeric, enantiomeric impurities, impurities in natural products, and finally degradation products. Examples are taken mainly from the author's own experience and from among the named impurities in the European Pharmacopoeia with focus on impurities in hydrocortisone, prednisolone, enalapril maleate, lisinopril, ethynodiol diacetate, pipecuronium bromide, cimetidine, and ethynylsteroids. The methodological aspects of impurity profiling from the detection to the identification/structure elucidation and quantitative determination of impurities are briefly summarized.

Procedimiento para la obtención de Cimetidina Polimorfo "A" a partir de Cimetidina Polimorfo "B" impuro / Method for obtaining \"A\" polymorph cimetidine from impure \"B\" polymorph cimetidine

Se describen procedimientos que permiten mediante cristalización en mezclas alcohol etílico-agua (solventes de producción nacional), obtener cimetidina polimorfo a que cumple los requerimientos de la Farmacopea de los EE.UU. a partir de polimorfos A y b impuros. Se estableció que si el contenido de impureza era igual o menor al doble del permitido, podía utilizarse alcohol etilico absoluto con un rendimiento en peso superior al 70 por ciento, pero si el contenido de impurezas estaba entre 2 y 3 veces, era necesario utilizar alcohol etílico con un contenido de agua del 6 por ciento y un rendimiento en peso del 60 al 65 por ciento. Se presentan además los resultados obtenidos durante su comprobación a escala industrial

Ion-pair solid-phase extraction of cimetidine from plasma and subsequent analysis by high-performance liquid chromatography.

An improved method is described for the solid-phase extraction of cimetidine from plasma or serum with subsequent analysis by HPLC. New aspects of the method include protein precipitation with metaphosphoric acid (5%, w/v), followed by selective adsorption of cimetidine and the internal standard ranitidine on the surface of a solid-phase phenyl (PH Bond Elut) column, using octanesulfonate as an ion-pairing agent. Separation was achieved on a LiChrosorb RP-18 column with a mobile phase consisting of acetonitrile-0.01 M phosphate buffer pH 3.0 containing 0.005 M octanesulfonate (22:78, v/v). The intra-assay coefficient of variation varied between 0.7 and 4.0%. The procedure provides cleaner and more stable samples and a better recovery (90 +/- 2.3%) and sensitivity (limit of detection 5 ng/ml and limit of quantitation 25 ng/ml) as compared with previous methods.