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A simple spectrophotometric method for the determination of cephadroxil in aqueous solution is developed. The method is based on the coupling of cephadroxil with diazotised sulphanilic acid reagent in the presence of sodium hydroxide. The yellow azo-dye formed is water– soluble, stable, and shows maximum absorption at 445 nm. Beer’s law is obeyed over the range 10–240 μg/25 ml (0.4 –9.6 ppm) with a molar absorptivity of 1.73×10 l.molcm, Sandell’s sensitivity index of 0.0210 μg/cm, a relative error of –0.42 to +2.22 % and a relative standard Diazotised Suhphanilic Acid Reagent for the Determination ... 24 deviation of ± 1.7 to ± 2.4 %, depending on the concentration level. The composition of the yellow azo-dye has been evaluated. The proposed method has been successfully applied to the determination of cephadroxil in various pharmaceutical preparations. Introduction Cephadroxil is an antibiotic in a class of drugs called cephalosporins. Cephadroxil is used to treat many different types of bacterial infections such as bronchitis, tonsillitis, ear infections, skin infections, and urinary tract infections. Cephadroxil may also be used for purposes other than those cited[1]. A variety of techniques has been used for the determination of cephadroxil: chromatography [2,3], flow injection [4,5], and fluorometry [6,7]. Also, various spectrophotometric methods have been used in determination of cephadroxil as pure and in pharmaceuitical preparations using reagents such as diazotised benzocaine in the presence of triethylamine [8], diazotised p-nitroaniline [9], 4-aminoantipyrine in the presence of an alkaline oxidizing agent (hexacyanopherateIII) [10], 3-methyl-2benzothiazolinone hydrazone hydrochloride in the presence of ceric ammonium sulphate, 4-aminophenazone in the presence of potassium hexacyanopherrate (III), 2,6-dichloroquinone-4-chlorimide [11], Cu(II) and V(V) in sulphuric acid [12], Folin-Ciocalteu reagent in presence of sodium hydroxide and stannous chloride [13], molybdophosphoric acid as an oxidising agent [14], Ce (IV) or Fe (III) [15], after nitration a subsequent complexation with an nucleophilic reagent, nitrosation and subsequent metal chelation, coupling with diazo reagent, and reaction with copper and extraction of the resulting chelate into chloroform [16]. However some of above methods suffer from several disadvantage such as the need for non aqueous medium [8] or extraction of the resulting dye into nonaqueous solvent [16]. The objective of the investigation reported in this paper is to evaluate a simple spectrophotometric method for the determination of cephadroxil; the method is based on coupling with diazotised sulphanilic acid in basic medium. The resulting yellow dye formed proves to be intense, water– soluble and stable. Nabeel Sabeh Othman & Shilan Ali Omer 25 Materials and Methods Apparatus The spectrophotometric measurements are carried out on Shimadzu UV-Visible Recording Spectrophotometric UV-160, using 1-cm silica cells. Reagents All chemicals used are of the highest purity available. Cephadroxil working solution, 100 μg / ml. A 0.01g amount of cephadroxil is dissolved in distilled water with warming, then the volume is completed to 100 ml in a volumetric flask, the solution is stable for one week at least. Diazotised sulphanilic acid reagent solution, 50 mM. A 0.865 g of sulphanilic acid is dissolved in about 75 ml of distilled water and the mixture is heated until the clear solution is obtained, , then 1 ml of concentrated hydrochloric acid is added, the mixture is then cooled to 0 5°C in an ice– bath, and a 0.345g sodium nitrite is added and stirred vigorously. After 5 minutes the solution is made up to volume in 100 ml volumetric flask with cooled distilled water, and is kept in a brown bottle in a refrigerator .This solution is prepared freshly each day [17]. Sodium hydroxide solution, 1N. This solution is prepared by appropriate dilution of the concentrated volumetric (Fluka) solution with distilled water and then transferred to a plastic bottle. Solution of pharmaceutical preparations Cephadroxil tablets solution, 100 μg.ml. Weigh and finely powder 10 tablets (each one contains 500 mg cephadroxil), an accurately weighed amount of powder equivalent to 0.01g cephadroxil is dissolved in 50 ml distilled water then the solution is warmed with shaking to increase the solubility, filtered into 100-ml calibrated flask, then the solution is completed to the volume with a distilled water. Cephadroxil capsule solution, 100μg.ml. Weigh and mix the contents of five capsules (each one contains 500 mg cephadroxil), an accurately weighed amount of powder equivalent to 0.01g cephadroxil is dissolved in 50 ml distilled water then the solution is warmed with shaking to increase the solubility, filtered into 100-ml calibrated flask, then the solution is completed to the volume with a distilled water. Cephadroxil suspension solution, 100μg.ml. This solution is prepared by dissolving the content of the container in mixture containing 5 ml of Diazotised Suhphanilic Acid Reagent for the Determination ... 26 hydrochloric acid (0.1N)and 10 ml of ethanol then the solution is diluted to 60 ml with distilled water (each 5ml contain 250 mg cephadroxil), after filteration of the solution, 2ml which equivalent to 0.1 g cephadroxil is transferred in to a 100-ml calibrated flask and the volume is completed with a distilled water.A 10 ml of the above solution is diluted to 100 ml to prepare 100μg mlsolution. Procedure and Calibration graph. To a series of 25ml volumetric flasks transfere 10 – 280 μg (0.4 – 11.2 ppm) of cephadroxil, 4 ml of diazotised sulphanilic acid (50mM) and 6 ml of 1N NaOH and the volumes are made to the mark with distilled water. The absorbances are read against a reagent blank, prepared in the same manner but without cephadroxil, at 445 nm using 1-cm cells. The calibration graph is linear over the range 10-240 μg/25ml (0.4–9.6 ppm) and higher concentrations show negative deviation (Fig.1). The molar absorptivity, calculated in the region of least photometric error and at the wavelength of maximum absorption, is found to be 1.73×10 l.mol.cm, with Sandell sensitivity index of 0.021 μg. cm. Fig. 1: Calibration graph of cephadroxil determination Results and Discussion For the subsequent experiments. 100 μg of cephadroxil is taken and final volumes are brought to 25 ml with distilled water. Absorption spectra. When cephadroxil in aqueous solution is treated with diazotized sulphanilic acid reagent solution, an absorption peak is obtained showing intense absorption at 445-nm characteristic of the yellow dye. The 445-nm wavelength of maximum absorption has been y = 0.0019x + 0.0156 r = 0.999222 0 0.1 0.2 0.3 0.4 0.5 0.6 0 50 100 150 200 250 300 μg of cephadroxil / 25 ml A bs or ba nc e Nabeel Sabeh Othman & Shilan Ali Omer 27 used in all subsequent experiments. The reagent blank shows very nill absorption (0.036) at the wavelength of maximum absorption (Fig.2). Fig. 2: Absorption spectra of 100μg cephadroxil / 25ml treated according to the recommended procedure and measured against (A) reagent blank, (B) distilled water and (C) reagent blank measured against distilled water Study of the optimum reaction conditions. The various parameters affecting and related to the yellow azo-dye have been studied and optimum conditions have been selected. Effect of base. The preliminary experiments have shown that the azo-dye develops only completely in alkaline medium. Different amounts of bases (strong and weak) have been used (Table1). Table 1: The effect of base on absorbance and colour contrast Absorbance* / ml of base used pH range 3.0 2.5 2.0 1.5 1.0 Variable Base used (1N) Solution 0.098 0.102 0.112 0.162 0.153 A 11.77-12.06 140 141 142 143 141 ∆λ∗∗, nm NaOH 0.126 0.107 0.111 0.128 0.150 A 11.84-12.23 140 140 141 142 141 ∆λ, nm KOH 0.549 0.457 0.378 0.360 0.341 A 9.70-9.96 37 47 40 39 42 ∆λ, nm Na2CO3*** 0.169 0.157 0.193 0.247 0.217 A 8.74-9.02 72 71 75 74 74 ∆λ, nm NaHCO3*** * Adding 1 ml diazotised sulphanilic acid ** ∆λ = λmaxSλmaxB where S=The dye, B=Blank *** Gives unstable azo-dye , Diazotised Suhphanilic Acid Reagent for the Determination ... 28 The experimental data show that sodium carbonate and sodium bicarbonate give better sensitivity than sodium hydroxide and potassium hydroxide. But the later bases give better colour contrast and the azo-dye formed has good stability compared with weak bases, so that 1.5 ml of 1N NaOH is recommended for the subsequent experiments. Effect of diazotized sulphanilic acid reagent amount. The effect of the amount of the diazotized sulphanilic acid on the maximum absorbance of the azo-dye formed from different amounts of cephadroxil has been investigated. The results show that 4 ml of diazotized sulphanilic acid (50mM) reagent solution gives the highest intensity with a correlation coefficient (r) of 0.998018 over a range of cephadroxil concentration 20–120 μg/25ml (Table2), therefore 4ml is recommended for the subsequent experiments. Table 2: The effect of diazotised sulphanilic acid amount on absorbance Absorbance / μg of cephadroxil present r 120 100 80 60 40 20 ml of Diazotised sulphanilic acid reagent solution (50 mM) 0.99027 0.187 0.158 0.113 0.083 0.067 0.04 1 0.997499 0.196 0.167 0.125 0.103 0.072 0.043 2 0.997485 0.200 0.179 0.145 0.117 0.079 0.048 3 0.998018 0.250 0.205 0.159 0.132 0.088 0.051 4 0.989547 0.256 0.192 0.151 0.124 0.081 0.055 5 Effect of surfactant Table 3 shows that an addition of surfactants gives no useful effect. Therefore, it has been recommended to eliminate the use of surfactants in the subsequent experiments. Table 3: Effect of surfactant. Absorbance* / order** of addition III II I ∆λ A ∆λ A ∆λ A Surfactant solution ... Turbid ... Turbid ... Turbid CPC, 1×10M 140 0.193 140 0.175 142 0.167 SDS, 1×10M 142 0.190 140 0.177 141 0.180 Triton X-100, 1% * Absorbance without surfactant = 0.210 ** I. Cephadroxil (C) + Surfactant (S) + dia

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Diazotised Suhphanilic Acid Reagent for the Determination of Trace Amounts of Cephadroxil in Aqueous Solution – Application to Pharmaceutical Preparations