Research Article Received: 5 August 2008, Accepted: 6 August 2008 Published online 17 November 2008 in Wiley Interscience (www.interscience.wiley.com) DOI 10.1002/bmc.1137 Copyright © 2008 John Wiley & Sons, Ltd. Biomed. Chromatogr. 2009; 23: 464– 471 464 John Wiley & Sons, Ltd. Determination of quinocide as impurity in primaquine tablets by capillary zone electrophoresis Determination of quinocide as impurity in primaquine tablets Abdalla A. Elbashir, a Bahruddin Saad, a Abdussalam Salhin Mohamed Ali, a Muhammad Idiris Saleh a and Hassan Y. Aboul-Enein b * ABSTRACT: A capillary zone electrophoretic method has been developed and validated for the determination of the impurity quinocide (QC) in the antimalarial drug primaquine (PQ). Different buffer additives such as native cyclodextrins and crown ethers were evaluated. Promising results were obtained when either b-cyclodextrin (b-CD) or 18-crown-6 ether (18C6) were used. Their separation conditions such as type of buffer and its pH, buffer additive concentration, applied voltage capillary temperature and injection time were optimized. The use of 18C6 offers slight advantages over b-CD such as faster elution times and improved resolution. Nevertheless, migration times of less than 5 min and resolution factors (R s ) in the range of 2–4 were obtained when both additives were used. The method was validated with respect to selectivity, linearity, limits of detection and quantita- tion, analytical precision (intra- and inter-day variability) and repeatability. Concentrations of 2.12 and 2.71% (w/w) of QC were found in pharmaceutical preparations of PQ from two different manufacturers. A possible mechanism for the successful separation of the isomers is also discussed. Copyright © 2008 John Wiley & Sons, Ltd. Keywords: capillary electrophoresis; primaquine; quinocide; β-cyclodextrin; 18-crown-6 ethers Introduction Malaria is one of the most widespread and prevalent endemic diseases, with 40% of the world’s population at risk. It is responsible for around 300–500 million incidences of illness and about 1.5–2.7 million deaths each year (WHO, 1993). It is caused by the protozoa Plasmodium vivax and other Plasmodium ssp. Despite much investigation, primaquine diphosphate [8- (4-amino-1-methylbutylamino)-6-methyoxyquinoline; Fig. 1] is the only available drug that is effective for the prevention of relapse of malaria (Hollingdale, 1988). Specifications regarding the purity of primaquine diphosphate (PQ) are less strictly regulated than those for most drugs used in the treatment of other diseases. The main contaminant to PQ was believed to be its enantiomer (Brondz et al., 2004), which was postulated to have the same toxicity as the main product. However, more recent work has revealed interesting new infor- mation about this drug. The work of Brondz et al. (2004, 2005a) (using HPLC, HPLC-MS and GC, GC-MS) and Dongre et al. (2005) (using HPLC, LC-MS/MS and GC-electron impact–mass spec- trometry) have independently and conclusively shown the major contaminant to be the positional isomer quinocide (QC), rather than the enantiomer. PQ and QC are highly toxic sub- stances which have a number of side effects when not properly administered Marrs et al. (1987). The main contaminant of the PQ drug is referred to as ‘related substances’ in the European Pharmacopoeia (2008), the United States Pharmacopeia (2008) and the British Pharmacopoeia (2003), and it is allowed to be present up to 3%. According to these pharmacopoeias, an HPLC method for the separation of PQ and ‘related substances# is described. Brondz et al. (2005b) reported HPLC and supercritical fluid chromatography (SFC) (Brondz et al., 2005c, 2007) methods for the separation of the QC from PQ. How- ever, the HPLC analysis time is rather long (over 30 min), in addition to the use of a more expensive chiral column. Using SFC equipped with a Discovery HS F5 column resulted in a marked reduction of the analysis time to 7 min Another drawback in some of these experiments (Brondz et al., 2005c) is that the impurity (QC) is eluted after the principle peak (PQ), which can lead to masking of the minor impurities. This can be a serious problem, especially when the resolution between the two peaks is low. Furthermore, the resolution obtained in these works is not sufficient, and therefore it is difficult to quantify the highly toxic contaminant QC in PQ. Recently Dongre et al. (2008) described a UPLC method for the determination of primaquine phosphate and its impurities. Probably one of the most powerful techniques for the separation of isomers is nowadays capillary electrophoresis (CE), due to its unsurpassed efficiency, speed and lower operating costs * Correspondence to: H. Y. Aboul-Enein, Pharmaceutical and Medicinal Chemistry Department, National Research Centre, Tahrir Street, Dokki, Cairo 12311, Egypt. E-mail: enein@gawab.com a School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia b Pharmaceutical and Medicinal Chemistry Department, National Research Centre, Tahrir Street, Dokki, Cairo 12311, Egypt Abbreviations used: 18C6, 18-crown-6 ether; α-CD, α-cyclodextrin; β-CD, β-cyclodextrin; CZE, capillary zone electrophoresis; PQ, primaquine; QC, quinocide. Contract/grant sponsor: Universiti Sains Malaysia. Contract/grant sponsor: Institute of Postgraduate Studies. USM.