Development of some Electroanalytical Methods for Detetection of Cephalexin and Amoxcillin

Abstract

Cephalosprins consist of a fused β-Lactam dihydrothiazine two ring system known as 7-amionocephalosporanic acid (ACA).The quantitative analysis of these compounds gives rise to many problems , due to the chemical instability of β-Lactam neucleus .Quantitative estimations of β-Lactam antbiotics have been based on measurments of colour reaction of their degradation products or formation of their derivatives, most of these quantitative estimations are not precise and they require expensive instruments, the objective of this study is to carry out these estimations with accurate conventionl and locally available instrumentalte techniques. Cephalosporins are organic acids, but with rather strong carboxylic group due to adjacent electronegative group ,with pK 1.7-2.6; therefore, they can be quantitatively determined ,titrimetrically ,conductometrically and potentiomertically in aqueous solutions . Two cephalosporins antibiotics in their pharmaceutical products, cephalexin and amoxicillin capsules,were used in this study, Cephalexin samples are products of Amipharma, Changahi, Elie and Wafra pharmaceutical companies in addition to cephlexin monohydrate used as a standard .Amoxicillin samples are products of Amipharma ,Changahi ,G.M, Wafra pharmaceutical companies in addition to amoxicillin tri hydrae used as astandard. In this study, aqueous sample solutions were conventionally titrated (directly and indirectly) and, potentiometrically, with sodium hydroxide, but, conductometrically with both sodium and ammonium hydroxide. Spectrophotometric and HPLC methods were also applied. Conductometric titration methods show one neutralizatin point for cephalexin and two neutralization points for amoxicillin. These two points indicate diprotic behavior of amoxicillin. due to the presence of phenolic ring in it,s structure which reacts with excess added base. It also forms intermolecular hydrogen bonding ,that facilitates deprotonating of the OH group of the phenolic ring to neutralize further the base to form the second point . For the same reason the potentiometric titration curves show two separate neutralization points for amoxicillin. The statistical analyses of the results obtained were carried out execluding that of the back titration method which gave very poor results due to the degradation of the antibiotics in alkaline medium. A significant difference at level (P< 0.001) was calculated for both cephalexin and amoxicillin results by direct titration, conductometric, potentiometric, spectrophotometric and HPLC methods. A significant difference at level ( P< 0.001) was calculatd for cephalexin results by direct titration , conductometrc and potentiometric methods . No significant difference at level ( P> 0.05 ) was calculated for results by direct titration, conductometric and potentiometric methods Statistically direct titration, coductometric, potentiometric, spectrophotometric and HPLC methods, show symmetrical mean results. The means results of direct titration, conductometric and potentiometric methods, show acceptable results as that of high performance liquid chromatography( HPLC)method.