Use of charge-transfer complexation in the spectrophotometric analysis of certain cephalosporins

Three simple, rapid and sensitive spectrophotometric procedures were develo ped for the analysis of cephapirin sodium (1), cefazoline sodium (2), cepha lexin monohydrate (3), cefadroxil monohydrate (4), cefotaxime sodium (5), c efoperazone sodium (6) and ceftazidime pentahydrate (7) in pure form as wel l as in their pharmaceutical formulations. The methods are based on the rea ction of these drugs as n-electron donors with the sigma -acceptor iodine, and the pi -acceptors: 2,3-dichloro-5,6-dicyano-p-benzo-quinone (DDQ) and 7 ,7,8,8-tetracyanoquinodimethane (TCNQ). Depending on the solvent polarity, different coloured charge-transfer complexes and radicals were developed. D ifferent variables and parameters affecting the reactions were studied and optimized. The obtained charge-transfer complexes were measured at 364 nm f or iodine tin 1,2-dichloroethane), 460 nm for DDQ tin methanol) and 843 nm for TCNQ tin acetonitrile). Ultraviolet-visible, infrared and H-1-nuclear m agnetic resonance techniques were used to study the formed complexes. Due t o the rapid development of colours at ambient temperature, the obtained res ults were used on thin-layer chromatograms for the detection of the investi gated drugs. Beer's plots were obeyed in a general concentration range of 6 -50, 40-300 and 4-24 mug ml(-1) with iodine, DDQ and TCNQ, respectively, wi th correlation coefficients not less than 0.9989. The proposed procedures c ould be applied successfully to the determination of the investigated drugs in vials, capsules, tablets and suspensions with good recovery; percent ra nged from 96.47 (+/- 1.14) to 98.72(+/- 1.02) in the iodine method, 96.35 ( +/- 1.62) to 98.51 (+/- 1.30) in the DDQ method, and 95.98 (+/- 0.78) to 98 .40 (+/- 0.87) in the TCNQ method. The association constants and standard f ree energy changes using Benesi-Hildebrand plots were studied. The binding of cephalosporins to proteins in relation to their molar absorptivities was studied. (C) 2001 Elsevier Science B.V. All rights reserved.