Journal of Pharmaceutical and Biomedical Analysis 27 (2002) 97–105 Determination of lignocaine and amprolium in pharmaceutical formulations using AAS W.F. El-Hawary Chemistry Department, Faculty of Science, Cairo Uniersity Giza, Egypt Received 30 March 2001; received in revised form 16 May 2001; accepted 29 May 2001 Abstract The ion-associate complexes of lignocaine hydrochloride (Lig.Cl) with ammonium reineckate (Rk) or sodium cobaltithiocyanate, and that of amprolium hydrochloride (Amp.Cl) with ammonium reineckate, have been prepared. The precipitated ion-associates were subjected to elemental analyses, infrared and nuclear magnetic resonance spectroscopy and determination of the metal content for elucidation of their structures. The solubilities of the solid ion-associate complexes have been studied and their solubility products were determined at different temperatures at the optimum pH for their quantitative precipitation. The thermodynamic parameters H, G and S for the dissolution of the ion-associate complexes were calculated. These ion-associate complexes have been used for the quantitative determination of the above mentioned drugs by precipitating them with an excess of the inorganic metal complex ions and determining the excess metal complex ions using atomic absorption spectrometry. The method was applied for the determination of the above drugs in pure solution and pharmaceutical preparations. 0.135 – 135.4 and 0.158 – 157.6 mg of lignocaine and amprolium, respectively, can be determined with mean relative standard deviations (R.S.D.) 0.92 – 1.20% and recovery values of 99.18 0.48 to 100.12 0.34% indicating high precision and accuracy. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Ion-associate complexes; Lignocaine; Amprolium; Atomic absorption spectrometry; Pharmaceutical analysis www.elsevier.com/locate/jpba 1. Introduction The investigated drugs are important pharma- ceutical compounds. Lignocaine hydrochloride (Lig.Cl) is a local anaesthetic of the amide type and is widely used by injection and for local applications to mucous membranes [1]. Ampro- lium hydrochloride (Amp.Cl 2 ) is an antiproto- zoal agent used in veterinary practice for the control of coccidiosis in poultry [1]. The pharmacopoeial methods for determina- tion of both lignocaine and amprolium depend on high performance liquid chromatography (HPLC) technique [2]. Several methods, also, have been reported for determination of ligno- caine; they include titrimetry [3,4], spectrophoto- metry [5–7], HPLC [8–10], TLC [11], GC [12–15] and potentiometry using ion selective electrodes [16–18]. Various techniques have been, also, used for determination of ampro- lium; including gravimetry [19], spectrophotome- try [20–22], HPLC [23–25], GC [26], TLC [27]and potentiometry using ion selective elec- trode [28]. 0731-7085/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0731-7085(01)00514-3