Research paper Iminodibenzyl as a novel coupling agent for the spectrophotometric determination of sulfonamide derivatives Padmarjaiah Nagaraja * , Kallanchira R. Sunitha, Ramanathapura A. Vasantha, Hemmige S. Yathirajan Department of Studies in Chemistry, University of Mysore, Mysore, India Received 23 May 2001; accepted in revised form 5 November 2001 Abstract A rapid, selective and simple spectrophotometric method for the determination of sulfa-drugs is described. The method is based on the formation of violet colored azo product by the diazotization of sulfonamides, viz. sulfathiazole (SFT), sulfadiazine (SFD), sulfacetamide (SFA), sulfamethoxazole (SFMx), sulfamerazine (SFMr), sulfaguanidine (SFG) and sulfadimidine (SFDd) followed by a coupling reaction with iminodibenzyl in alcohol medium. Absorbance of the resulting violet azo product is measured at 570–580 nm and is stable for 24 h at 278C. Beer’s law is obeyed in the concentration range of 0.05–6.0 mg ml 21 at the wavelength of maximum absorption. The method is successfully employed for the determination of sulfonamides in various pharmaceutical preparations and common excipients used as additives in pharmaceuticals do not interfere in the proposed method. The method offers the advantages of simplicity, rapidity and sensitivity without the need for extraction or heating. A reaction mechanism is proposed for the formation of the violet azo product. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Sulfa-drugs; Iminodibenzyl; Diazotization; Spectrophotometry; Pharmaceuticals 1. Introduction Sulfa-drugs are widely used in the treatment of infections, especially for patients intolerant to antibiotics. The vast commercial success of these medicinal agents has made the chemistry of sulfonamides to become a major area of research and an important branch of commercial importance in pharmaceutical sciences. A survey of literature reveals that there are various methods available for the determina- tion of sulfonamide derivatives, which suffer in one way or the other. The official method of British Pharmacopoeia [1] and United States Pharmacopoeia [2] describes nitrite titra- tion method for the analysis of sulfa-drugs. The other meth- ods include gas chromatography [3], high-performance liquid chromatography (HPLC) [4,5], HPTLC [6] electro- analytical methods [7–10], potentiometry [11], immuno- chemical assay [12], volumetric method [13,14], and spec- trofluorimetry [15]. The most important spectrophotometric methods, which have already been reported [16–29], for the determination of sulfa-drugs suffer from disadvantages like lack of sensitivity, involves heating or extraction, requires long time for the completion of reaction, narrow detection limit etc. A comparison of some spectrophotometric meth- ods for the analysis of sulfonamide derivatives are presented in Table 1. The purpose of this work is to introduce iminodibenzyl as a new coupling agent for the first time, which is economic- ally cheaper and sensitive than the most widely used coupling agents, viz. N-(1-naphthyl)-ethylenediamine dihy- drochloride (NEDA) and 3-methyl-benzothiazoline hydra- zone hydrochloride (MBTH), which are used for the determination of various organic compounds, i.e. phenols, polyhydroxy compounds, aromatic and aliphatic amines, alicyclic amines, bilirubin etc. In the present investigations, the diazotized sulfa-drug is coupled with iminodibenzyl in alcohol to give a violet azo product which is stable for 24 h. 2. Materials and methods 2.1. Instrument A JASCO MODEL UVIDEC-610 UV–VIS spectrophot- ometer with 1.0 cm matched cells was used for electronic spectral measurements. European Journal of Pharmaceutics and Biopharmaceutics 53 (2002) 187–192 0939-6411/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S0939-6411(01)00235-1 www.elsevier.com/locate/ejphabio * Corresponding author. University of Mysore, Manasagangotri, Mysore 570 006, India. Tel.: 191-821-541475; fax: 191-821-421263. E-mail address: nagarajap@mailcity.com (P. Nagaraja).