Journal of Chromatography B, 800 (2004) 203–209 Capillary electrophoresis method for simultaneous determination of penicillin G, procaine and dihydrostreptomycin in veterinary drugs Katarzyna Michalska ∗ , Genowefa Pajchel, Stefan Tyski Antibiotics and Microbiology Department, National Institute of Public Health, 30–34 Chelmska Street, 00-725 Warsaw, Poland Abstract Capillary electrophoresis method for identification and simultaneous determination of procaine, dihydrostreptomycin and penicillin G, present in multiantibiotic veterinary preparations, was elaborated. The influence of pH (5.0–9.75) and concentration of disodium tetraborate decahydrate in running buffers (0.02–0.1 M) as well as temperatures (25–40 ◦ C) on separation efficacy were analyzed. For quantitative analysis, 0.08 M borate buffer (pH 8.0) at 35 ◦ C and 15kV were chosen. Method was validated, selectivity, precision, linearity, LOD, LOQ, accuracy and specificity of capillary zone electrophoresis (CZE) were evaluated. © 2003 Elsevier B.V. All rights reserved. Keywords: Dihydrostreptomycin; Procaine; Penicillin G 1. Introduction The combination of compounds belonging to different antibiotic groups is sometimes used in the veterinary phar- maceutical preparations. Most frequently aminoglycosides are combined with -lactams [1] in order to obtain synergy interaction and to broaden the spectrum of antimicrobial activity. Benzylpenicillin might be applied in the drug as procaine salt to get slower absorption and therefore longer lasting activity (Fig. 1). Dihydrostreptomycin sulfate (DHS) (Fig. 2) assay is a critical point for simultaneous determination of analyzed compounds, because lack of suitable strong UV chromopho- res or fluorophores in aminoglycoside antibiotics, makes as- say very difficult. Several methods for DHS determination in pharmaceu- tical preparations are available in the publications. Most pharmacopoeias have recommended the microbiological determination of DHS, however, existing other analytical methods involve separation techniques such as high per- formance liquid chromatography (HPLC) or capillary zone electrophoresis (CZE). In the HPLC method, ion-pair re- ∗ Corresponding author. Tel.: +48-22-841-36-83; fax: +48-22-841-06-52. E-mail address: tyski@il.waw.pl (K. Michalska). versed phase with UV detection at 195 or 205 nm can be applied [2]. DHS, streptomycin and related substances can also be analyzed by CZE with direct UV detection at 205 nm, using borate complexation at pH 10.25 [3,4]. Indirect UV detection in the anionic mode with a reversed electroosmotic flow (EOF) by addition of fluorochemical surfactant FC 135 to the background electrolyte (BGE) was also applied [5,6]. The routine determination of benzylpenicillin, procaine and dihydrostreptomycin in multiantibiotic drug is per- formed by HPLC using ion-pair reversed phase and ultravi- olet detection at 205, 210 or 224 nm [1]. The aim of this study was to adapt capillary electrophore- sis system for determination of procaine benzylpenicillin and DHS, components of Veti-ps drug, simultaneously and to validate elaborated assay. 2. Experimental 2.1. Apparatus Capillary electrophoresis experiments were carried out on QUANTA 4000E CE system (Waters, Milford, MA, USA) suitable to perform both hydrodynamic and voltage injection, equipped with a 30 kV power supply, an UV spectrophotometric detector, connected to a data collection 1570-0232/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jchromb.2003.10.017