Validation and application of an HPLC-CAD-TOF/MS method for identification and quantification of pharmaceutical counterions.

A generic approach for the analysis of counterions of pharmaceutical reference substances, which are established by the laboratory department of the European Pharmacopoeia (Ph. Eur.), was developed. A mixed-mode chromatography method using charged aerosol detection (CAD) published by Zhang et al. separating 25 commonly used pharmaceutical counterions was selected for this purpose. The method was validated in terms of specificity, repeatability, limits of quantification (LOQs), linearity and range according to ICH guideline Q2(R1) and the Technical Guide for the Elaboration of Monographs of the Ph. Eur. Moreover, the applicability of the method for the purpose of counterion identification and quantification in drug substances as well as for the control of inorganic ions as impurities was demonstrated using selected examples of Ph. Eur. reference standards and other samples of substances for pharmaceutical use (e.g. cloxacillin sodium, somatostatin). It was shown that for identification purposes of the parent substance as well as organic ions the chromatographic system can easily be coupled to a mass selective detector without any modification.

Determination of the impurity profile of adenosine by means of ion-pair reversed-phase chromatography.

Production processes of adenosine include condensation of ribose and adenine by means of chemical or biochemical processes, as well as fermentation. Nowadays, adenosine is commonly produced by alkaline hydrolysis of yeast ribonucleic acid, often in the presence of calcium or lead ions, followed by chromatographic separation of the obtained nucleosides adenosine, cytidine, guanosine and uridine. The current Ph. Eur. monograph for adenosine describes a TLC method for determination of related substances that limits the impurities to 1 per cent. To ensure the quality of adenosine, it is proposed to replace the TLC method by a more sensitive and selective HPLC method, in accordance with the current policy for control of impurities as defined by the Ph. Eur. Commission. An HPLC separation system, originally proposed by the USP, using ion-pair reversed-phase chromatography in combination with tetrabutylammonium hydrogen sulphate as an ion-pair reagent, has been examined for its suitability to limit guanosine, inosine, uridine and adenine. This article describes the experiments as regards the choice of the most suitable commercial column to obtain an appropriate separation, the column temperature, the establishment of a relevant system suitability criterion, and the determination of correction factors for the individual impurities.