Spectrophotometric study of the reaction mechanism between DDQ as pi-acceptor and potassium iodate and flucloxacillin and dicloxacillin drugs and their determination in pure and in dosage forms

Two simple and accurate spectrophotometric methods are presented for the determination of beta-lactam drugs, flucloxacillin (Fluclox) and dicloxacillin (Diclox), in pure and in different pharmaceutical preparations. The charge transfer (CT) reactions between Fluclox and Diclox as electron donors and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) pi-acceptor and potassium iodate via oxidation reduction reaction where the highly coloured complex species or the liberated iodine have been spectrophotometrically studied. The optimum experimental conditions have been studied carefully. Beer's law is obeyed over the concentration range of 2-450 microg ml(-1) for Fluclox and 10-450 microg ml(-1) for Diclox using DDQ reagent and at 50-550 microg ml(-1) for Fluclox and 50-560 microg ml(-1) for Diclox using iodate method, respectively. For more accurate results, Ringbom optimum concentration range is calculated and found to be 6-450 and 15-450 microg ml(-1) for Fluclox and Diclox using DDQ, respectively, and 65-550 and 63-560 microg ml(-1) for Fluclox and Diclox using iodine, respectively. The Sandell sensitivity is found to be 0.018 and 0.011 microg cm(-2) for DDQ method and 0.013 and 0.011 microg cm(-2) for iodate method for Fluclox and Diclox, respectively, which indicates the high sensitivity of both methods. Standard deviation (S.D.=0.01-0.80 and 0.07-0.98) and relative standard deviation (R.S.D.=0.13-0.44 and 0.11-0.82%) (n=5) for DDQ and iodate methods, respectively, refer to the high accuracy and precision of the proposed methods. These results are also confirmed by between-day precision of percent recovery of 99.87-100.2 and 99.90-100% for Fluclox and Diclox by DDQ method and 99.88-100.1 and 99.30-100.2% for Fluclox and Diclox by iodate method, respectively. These data are comparable to those obtained by British and American pharmacopoeias assay for the determination of Fluclox and Diclox in raw materials and in pharmaceutical preparations.     

Utility of some pi-acceptors for spectrophotometric determination of gatifloxacin in pure form and in pharmaceutical preparations

Four simple, quick and sensitive methods are described for the spectrophotometric determination of gatifloxacin. The methods are based on the reaction of gatifloxacin as n-electron donor with 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); chloranilic acid (CLA) and p-chloranil (CL) as pi-acceptors to give highly colored complex species. The colored products are quantitated spectrophotometrically at 460, 841, 530 and 545 nm for DDQ, TCNQ, CLA and CL, respectively. Optimization of the different experimental conditions is described. Beer's law is obeyed in the concentration ranges 5-60, 1.5-18, 30-360 and 20-240 microg ml(-1) of gatifloxacin, but for more accurate analysis, Ringbom optimum concentration range was found to be 7.5-55, 3-16, 35-350 and 25-230 microg ml(-1) of gatifloxacin for DDQ, TCNQ, CLA and CL, respectively. The limits of detection and quantification were calculated and the relative standard deviations for different concentrations of gatifloxacin using various acceptors were <1.28%. The association constants of 1 : 1 complexes and standard free energy changes using Benesi-Hildebrand plots were studied. The proposed methods were successfully applied to the determination of gatifloxacin in pharmaceutical dosage forms without interference from common additives encountered.     

Facile colorimetric methods for the quantitative determination of tetramisole hydrochloride

A facile, rapid and sensitive methods for the determination of tetramisole hydrochloride in pure and in dosage forms are described. The procedures are based on the formation of coloured products with the chromogenic reagents alizarin blue BB (I), alizarin red S (II), alizarin violet 3R (III) and alizarin yellow G (IV). The coloured products showed absorption maxima at 605, 468, 631 and 388 nm for I-IV, respectively. The colours obtained were stable for 24 h. The colour system obeyed Beer's law in the concentration range 1.0-36, 0.8-32, 1.2-42 and 0.8-30 microg ml(-1) respectively. The results obtained showed good recoveries with relative standard deviations of 1.27, 0.96, 1.13 and 1.35%, respectively. The detection and determination limits were found to be 1.0 and 3.8, 1.2 and 4.2, 1.0 and 3.9 and finally 1.4 and 4.8 ng ml(-1) for I-IV complexes, respectively. Applications of the method to representative pharmaceutical formulations are represented and the validity assessed by applying the standard addition technique, which is comparable with that obtained using the official method.     

Validated spectrophotometric and fluorimetric methods for analysis of clozapine in tablets and urine

Five spectrophotometric methods and one fluorimetric method have been developed and validated for the analysis of clozapine. The spectrophotometric methods were based on the charge-transfer complexation reaction between clozapine as electron donor and each of iodine as sigma-acceptor or 7,7,8,8-tetracyanoquinondimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzo-quinone (DDQ), tetracyanoethane (TCNE), and p-chloranilic acid (pCA) as pi-acceptors. The obtained complexes were measured spectrophotometrically at 365, 843, 460, 414, and 520 nm for iodine, TCNQ, DDQ, TCNE, and pCA, respectively. The fluorimetric method was based on the oxidation of clozapine in the presence of perchloric acid by cerium (IV), and subsequent measuring the fluorescence of the produced cerium (III) fluorimetrically at lambda(excitation) 260 and lambda(emission) 355 nm. Under the optimum assay conditions, Beer's law was obeyed at concentrations ranged from 4-200 microg mL(-1) for the spectrophotometric methods and from 24-250 ng mL(-1) for the fluorimetric method. The limits of detection for the spectrophotometric methods were 1.12, 1.76, 2.22, 0.95, and 13.26 microg mL(-1) for iodine, TCNQ, DDQ, TCNE, and pCA, respectively. The limit of detection for the fluorimetric method was 6.69 ng mL(-1). The proposed methods were successfully applied to the analysis of clozapine in tablets with good recoveries. The fluorimetric method could also be applied to the analysis of clozapine in spiked urine samples. The molar ratios and the reaction mechanisms were investigated.     

Spectrophotometric determination of rifampicin through chelate formation and charge transfer complexation in pharmaceutical preparation and biological fluids

Two simple and accurate spectrophotometric methods for determination of Rifampicin (RIF) are described. The first method is based on charge transfer (CT) complex formation of the drug with three pi-electron acceptors either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,7,7,8-Tetracyanoquinodimethane (TCNQ) or 2,3,5,6-Tetrachloro-1,4-benzoquinone (p-chloranil) in acetonitrile. The method is followed spectrophotometrically by measuring the maximum absorbance at 584 nm, 761 nm (680 nm) or 560 nm for DDQ, TCNQ and p-chloranil, respectively. Under the optimized experimental conditions, the calibration curves showed a linear relationship over the concentration ranges of 5-140 microg/ml, 2-45 microg/ml (5-120 microg/ml) and 15-200 microg/ml, respectively. The second method is based on the reaction of RIF with iron(III) forming a water insoluble violet complex which is extracted into chloroform. The method determines RIF in concentration range of 10-240 microg/ml at 540 nm. The proposed methods applied to determination of RIF in capsule, human serum and urine samples with good accuracy and precision. The results were compared statistically with the official method and showed no significant different between the methods compared in terms of accuracy and precision.     

Spectrophotometric and spectrofluorimetric methods for analysis of acyclovir and acebutolol hydrochloride

Simple and sensitive spectrophotometric and spectrofluorimetric methods are described for analysis of acebutolol hydrochloride. The proposed methods are based on oxidation of the selected drug with cerium(IV) ion in acidic medium with subsequent measurement of either the decrease in absorbance at 320 nm or the fluorescence intensity of the produced cerous(III) ion at 363 nm (excitation at 250 nm). Beer's law obeyed from 1.0-7.0 microg ml(-1) and 0.25-2.5 microg ml(-1) acebutolol hydrochloride, using the spectrophotometric and spectrofluorimetric method, respectively. The proposed methods were successfully applied for determination of the selected drug in its pharmaceutical preparation with good recoveries.     

Validated spectrophotometric methods for the determination of amiodarone hydrochloride in commercial dosage forms using p-chloranilic acid and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

Two simple, sensitive and economical spectrophotometric methods have been developed for the determination of amiodarone hydrochloride in pure form and commercial dosage form. These methods (A and B) are based on the reaction of amiodarone base as n-electron donor with p-chloranilic acid and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as pi-acceptors to give highly colored complex species which absorb maximally at 535 and 570 nm, respectively. Beer's law is obeyed in the concentration ranges 10.0 - 360.0 and 2.0 - 65.0 microg ml(-1) for methods A and B, respectively. Application of the proposed methods to commercial pharmaceutical tablets are presented.     

Spectrophotometric and potentiometric determination of piroxicam and tenoxicam in pharmaceutical preparations

Two simple and accurate methods are described for the determination of piroxicam and tenoxicam in their pharmaceutical preparations. The spectrophotometric method involves the oxidation of these drugs with potassium iodate in acid medium with the liberation of iodine and subsequent extraction with cyclohexane followed by measuring the absorbance at lambda=522 nm. Beer's law is obeyed in the concentration range of 0.05-1.1 and 0.05-0.6 mg x ml(-1) for piroxicam and tenoxicam, respectively. The apparent molar absorptivities of the resulting coloured products are found to be 2.7 x 10(3) and 2.5 x 10(3) l mol(-1) x cm(-1), whereas Sandell sensitivities are 0.012 and 0.013 g x cm(-2) for piroxicam and tenoxicam, respectively. The potentiometric method involves the direct titration of both drugs with N-bromosuccinimide in acid medium and the end point is determined potentiometrically using platinum indicator electrode. Piroxicam and tenoxicam can be determined quantitatively in the concentration range of 0.33-3.37 and 0.33-4.08 mg x ml(-1) for tenoxicam and piroxicam, respectively. The standard deviation and relative standard deviation values are found to be ranged from 0.05-0.07 and 0.37-0.98% and 0.025-0.078 and 0.25-1.2% for tenoxicam and piroxicam, respectively. The two methods are accurate within +/-1.0%. Optimum conditions affecting both methods are studied. The proposed methods are applied for the determination of the drugs in pure form and in commercial pharmaceutical preparations.     

Spectrophotometric, spectrofluorometric and HPLC determination of desloratadine in dosage forms and human plasma

Four sensitive, simple and specific methods were developed for the determination of desloratadine (DSL), a new antihistaminic drug in pharmaceutical preparations and biological fluids. Methods I and II are based on coupling DSL with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in borate buffer of pH 7.6 where a yellow colored reaction product was obtained and measured spectrophotometrically at 485 nm (Method I). The same product could be measured spectrofluorometrically at 538 nm after excitation at 480 nm (Method II). Methods III and IV, on the other hand, involved derivatization of DSL with 2,4-dinitrofluorobenzene (DNFB) in borate buffer of pH 9.0 producing a yellow colored product that absorbs maximally at 375 nm (Method III). The same derivative was determined after separation adopting HPLC (Method IV). The separation was performed on a column packed with cyanopropyl bonded stationary phase equilibrated with a mobile phase composed of acetonitrile-water (60 : 40, v/v) at a flow rate of 1.0 ml min(-1) with UV detection at 375 nm. The calibration curves were linear over the concentration ranges of 0.5-6, 0.02-0.4, 1-10 and 1-30 microg ml(-1) for Methods I, II, III and IV, respectively. The lower detection limits (LOD) were 0.112, 0.004, 0.172 and 0.290 microg ml(-1), respectively, for the four methods. The limits of quantification (LOQ) were 0.340, 0.012, 0.522 and 0.890 microg ml(-1) for Methods I, II, III and IV, respectively. The proposed methods were applied to the determination of desloratadine in its tablets and the results were in agreement with those obtained using a reference method. Furthermore, the spectrofluorometric method (Method II) was extended to the in-vitro determination of the drug in spiked human plasma, with a mean percentage recovery (n=4) of 99.7+/-3.54. Interference arising from endogenous amino acids has been overcome using solid phase extraction. The proposed methods are highly specific for determination of DSL in the presence of the parent drug loratadine. A proposal for the reaction pathways is postulated.     

Spectrophotometric determination of iodine species in table salt and pharmaceutical preparations

A sensitive spectrophotometric method for the determination of iodine species like iodide, iodine, iodate and periodate is described. The method involves the oxidation of iodide to ICl(2)(-) in the presence of iodate and chloride in acidic medium. The formed ICl(2)(-) bleaches the dye methyl red. The decrease in the intensity of the colour of the dye is measured at 520 nm. Beer's law is obeyed in the concentration range 0-3.5 microg of iodide in an overall volume of 10 ml. The molar absorptivity of the colour system is 1.73 x 10(5) l mol(-1) cm(-1) with a correlation coefficient of -0.9997. The relative standard deviation is 3.6% (n=10) at 2 microg of iodide. The developed method can be applied to samples containing iodine, iodate and periodate by prereduction to iodide using Zn/H(+) or NH(2)NH(2)/H(+). The effect of interfering ions on the determination is described. The proposed method has been successfully applied for the determination of iodide and iodate in salt samples and iodine in pharmaceutical preparations.     

Spectrophotometric and spectrodensitometric determination of paracetamol and drotaverine HCl in combination

Thin-layer chromatography, first derivative, ratio spectra derivative spectrophotometry and Vierordt's method have been developed for the simultaneous determination of paracetamol and drotaverine HCl. TLC densitometric method depends on the difference in Rf values using ethyl acetate:methanol:ammonia (100:1:5 v/v/v) as a mobile phase. The spots of the two drugs were scanned at 249 and 308 nm over concentration ranges of 60-1200 microg/ml and 20-400 microg/ml with mean percentage recovery 100.11%+/-1.91 and 100.15%+/-1.87, respectively. The first derivative spectrophotometric method deals with the measurements at zero-crossing points 259 and 325 nm with mean percentage recovery 99.25%+/-1.08 and 99.45%+/-1.14, respectively. The ratio spectra first derivative technique was used at 246 and 305 nm with mean percentage recovery 99.75%+/-1.93 and 99.08%+/-1.22, respectively. Beer's law for first derivative and ratio spectra derivative methods was obeyed in the concentration range 0.8-12.8 and 0.4-6.4 microg/ml of paracetamol and drotaverine HCl, respectively. Vierordt's method was applied to over come the overlapping of paracetamol and drotaverine HCl in zero-order spectra in concentration range 2-26 and 2-40 microg/ml respectively. The suggested methods were successfully applied for the analysis of the two drugs in laboratory prepared mixtures and their pharmaceutical formulation. The validity of the methods was assessed by applying the standard addition technique. The obtained results were statistically agreed with those obtained by the reported method.     

Spectrophotometric determination of flucloxacillin and dicloxacillin in pure and dosage forms

A simple, rapid and accurate spectrophotometric method for the determination of antibiotic drugs, flucloxacillin (Fluclox) and dicloxacillin (Diclox), in pure form and different pharmaceutical preparations has been developed. The charge transfer (CT) reactions between Fluclox and Diclox as electron donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE) as pi-acceptors to give highly coloured complex species have been spectrophotometrically studied. The optimum experimental conditions for these CT reactions have been studied carefully. Beer's law is obeyed over the concentration ranges of 4-180 microg mL(-1) and 4-70 microg mL(-1) for Fluclox and Diclox drugs using TCNQ and TCNE reagents, respectively. The Sandell sensitivities (S) are found to be 0.016-0.035 microg cm(-2) and 0.011-0.016 microg cm(-2) for Fluclox and Diclox, respectively, which indicate the high sensitivity of the proposed method. The relative standard deviations (R.S.D.: 0.08-0.49 and 0.15-0.80) for the determination of Fluclox and (R.S.D.: 0.05-0.75 and 0.13-0.75) for Diclox were obtained for four to six replicates using TCNQ and TCNE reagents, respectively, refer to the high accuracy and precision of the proposed method. These results are also confirmed by the between-day precision and the percent recovery of 99.90-100.1 and 99.60-100.4 for Fluclox and 99.90-100.5 and 99.40-100.1 for Diclox using TNCQ and TCNE reagents, respectively. The results obtained for the two reagents are comparable with those obtained by the official method.     

Spectrophotometric determination of ternary mixtures of thiamin, riboflavin and pyridoxal in pharmaceutical and human plasma by least-squares support vector machines.

Ternary mixtures of thiamin, riboflavin and pyridoxal have been simultaneously determined in synthetic and real samples by applications of spectrophotometric and least-squares support vector machines. The calibration graphs were linear in the ranges of 1.0 - 20.0, 1.0 - 10.0 and 1.0 - 20.0 microg ml(-1) with detection limits of 0.6, 0.5 and 0.7 microg ml(-1) for thiamin, riboflavin and pyridoxal, respectively. The experimental calibration matrix was designed with 21 mixtures of these chemicals. The concentrations were varied between calibration graph concentrations of vitamins. The simultaneous determination of these vitamin mixtures by using spectrophotometric methods is a difficult problem, due to spectral interferences. The partial least squares (PLS) modeling and least-squares support vector machines were used for the multivariate calibration of the spectrophotometric data. An excellent model was built using LS-SVM, with low prediction errors and superior performance in relation to PLS. The root mean square errors of prediction (RMSEP) for thiamin, riboflavin and pyridoxal with PLS and LS-SVM were 0.6926, 0.3755, 0.4322 and 0.0421, 0.0318, 0.0457, respectively. The proposed method was satisfactorily applied to the rapid simultaneous determination of thiamin, riboflavin and pyridoxal in commercial pharmaceutical preparations and human plasma samples.     

Spectrophotometric determination of carbamazepine and mosapride citrate in pure and pharmaceutical preparations

Simple, rapid and sensitive spectrophotometric methods were developed for the determination of carbamazepine and mosapride citrate drugs in pure and pharmaceutical dosage forms. These methods are based on ion pair and charge transfer complexation reactions. The first method is based on the reaction of the carbamazepine drug with Mo(V)–thiocyanate in hydrochloric acid medium followed by an extraction of the coloured ion-pair with 1,2-dichloroethane and the absorbance of the ion pair was measured at 470 nm. The second method is based on the formation of ion-pairs between mosapride citrate and two dyestuff reagents namely bromothymol blue (BTB) and bromocresol green (BCG) in a universal buffer of pH 4 and 3, respectively. The formed ion-pairs are extracted with chloroform and methylene chloride and measured at 412 and 416 nm for BTB and BCG reagents, respectively. The third method is based on charge transfer complex formation between mosapride citrate (electron donor) and DDQ (π-acceptor reagent) and the absorbance of the CT complexes was measured at 450 nm. All the optimum conditions are established. The calibration graphs are rectilinear in the concentration ranges 10–350 for carbamazepine using Mo(V)–thiocyanate and 4–100, 4–60 and 10–150 μg mL^?1 for mosapride citrate using BTB, BCG and DDQ reagents, respectively. The Sandell sensitivity (S), molar absorptivity, correlation coefficient, regression equations and limits of detection (LOD) and quantification (LOQ) are calculated. The law values of standard deviation (0.04–0.09 for carbamazepine using Mo(V)–thiocyanate and 0.022–0.024, 0.013–0.018 and 0.013–0.020 for mosapride citrate using BTB, BCG and DDQ, respectively) and relative standard deviation (0.630–2.170 for carbamazepine using Mo(V)–thiocyanate and 0.123–1.43, 0.102–0.530 and 0.226–1.280 for mosapride citrate using BTB, BCG and DDQ, respectively) reflect the accuracy and precision of the proposed methods. The methods are applied for the assay of the two investigated drugs in pharmaceutical dosage forms. The results are in good agreement with those obtained by the official method.     

Spectrophotometric determination of selenium by use of thionin

A simple, rapid, and sensitive spectrophotometric method has been developed for the determination of selenium in real samples of water, soil, plant materials, human hair, and synthetic cosmetic and in pharmaceutical preparations. The method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine. The liberated iodine bleaches the violet color of thionin, and which is measured at 600 nm. This decrease in absorbance is directly proportional to selenium concentration and obeys Beer's law in the range 1-5 micro g selenium in a final volume of 10 mL (0.1-0.5 microg mL(-1)). The molar absorptivity and Sandell's sensitivity of the method were found to be 7.33 x 10(4) L mol(-1) cm(-1) and 0.0011 microg cm(-2), respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described.     

一种碘/氯摩尔比等于1的韦氏试剂制备方法和用于碘值测定

报道一种碘／氯摩尔比等于１的韦氏试剂的制备方法，并与国际标准的中国国定标准方法对照，测定了３个代表性样品的碘值。结果表明：用本法制备的韦氏试剂的碘值测定精密度远高于其他两人。     

Spectrophotometric study of the charge transfer complexes of some pharmaceutical butyrophenones

The molecular interactions between haloperidol and droperidol as electron donors and each of iodine; 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); tetracyanoethylene (TCNE); 2,4,7-trinitro-9-fluorenon (TNF); and 2-3-5-6-tetrabromo-1,4-benzoquinone (Bromanil) as acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studies and optimized. Beer's law was obeyed in a concentration limit of 2.5-2500 mug ml(-1) for the studied drugs with various acceptors used. Electron affinities (E(A)) of the acceptors were found to correlate with both the time required for maximum colour formation and the molar absorptivities of haloperidol and droperidol. A Job's plot of the absorbance versus the molar ratio of the drugs to iodine indicated 1:1 ratio. The proposed methods were found to be rapid and sensitive and may be applied for estimation of named drugs in pharmaceutical dosage forms without interferences from the common additives encountered. Percentage recoveries ranged from 99.1-102.2%.     

Simultaneous determination of cyproterone acetate and ethinylestradiol in tablets by derivative spectrophotometry

Derivative spectrophotometry offers a useful approach for the analysis of drugs in multi-component mixtures. In this study a third-derivative spectrophotometric method was used for simultaneous determination of cyproterone acetate and ethinylestradiol using the zero-crossing technique. The measurements were carried out at wavelengths of 316 and 226 nm for cyproterone acetate and ethinylestradiol respectively. The method was found to be linear (r2>0.999) in the range of 0.5-6 mg/100 ml for cyproterone acetate in the presence of 35 microg/100 ml ethinylestsradiol at 316 nm. The same linear correlation (r2>0.999) was obtained in the range of 10-80 microg/100 ml of ethinylestradiol in the presence of 2 mg/100 ml of cyproterone acetate at 226 nm. The limit of determination was 0.5 mg/100 ml and 10 microg/100 ml for cyproterone acetate and ethinylestradiol respectively. The method was successfully applied for simultaneous determination of cyproterone acetate and ethinylestradiol in pharmaceutical preparations without any interferences from excipients.     

Validated spectrophotometric methods for the estimation of moxifloxacin in bulk and pharmaceutical formulations

New, simple, cost effective, accurate and reproducible UV-spectrophotometric methods were developed and validated for the estimation of moxifloxacin in bulk and pharmaceutical formulations. Moxifloxacin was estimated at 296 nm in 0.1N hydrochloric acid (pH 1.2) and at 289 nm in phosphate buffer (pH 7.4). Beer's law was obeyed in the concentration range of 1-12 microg ml(-1) (r2=0.9999) in hydrochloric acid and 1-14 microg ml(-1) (r2=0.9998) in the phosphate buffer medium. The apparent molar absorptivity and Sandell's sensitivity coefficient were found to be 4.63 x 10(4) l mol(-1) cm(-1) and 9.5 ng cm(-2)/0.001 A in hydrochloric acid; and 4.08 x 10(4) l mol(-1) cm(-1) and 10.8 ng cm(-2)/0.001 A in phosphate buffer media, respectively indicating the high sensitivity of the proposed methods. These methods were tested and validated for various parameters according to ICH guidelines. The detection and quantitation limits were found to be 0.0402, 0.1217 microg ml(-1) in hydrochloric acid and 0.0384, 0.1163 microg ml(-1) in phosphate buffer medium, respectively. The proposed methods were successfully applied for the determination of moxifloxacin in pharmaceutical formulations (tablets, i.v. infusions, eye drops and polymeric nanoparticles). The results demonstrated that the procedure is accurate, precise and reproducible (relative standard deviation <2%), while being simple, cheap and less time consuming and hence can be suitably applied for the estimation of moxifloxacin in different dosage forms and dissolution studies.     

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

Three simple, rapid and sensitive spectrophotometric procedures were developed for the analysis of cephapirin sodium (1), cefazoline sodium (2), cephalexin monohydrate (3), cefadroxil monohydrate (4), cefotaxime sodium (5), cefoperazone sodium (6) and ceftazidime pentahydrate (7) in pure form as well as in their pharmaceutical formulations. The methods are based on the reaction of these drugs as n-electron donors with the σ-acceptor iodine, and the π-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. Different variables and parameters affecting the reactions were studied and optimized. The obtained charge-transfer complexes were measured at 364 nm for iodine (in 1,2-dichloroethane), 460 nm for DDQ (in methanol) and 843 nm for TCNQ (in acetonitrile). Ultraviolet–visible, infrared and ¹H-nuclear magnetic resonance techniques were used to study the formed complexes. Due to the rapid development of colours at ambient temperature, the obtained results were used on thin-layer chromatograms for the detection of the investigated drugs. Beer's plots were obeyed in a general concentration range of 6–50, 40–300 and 4–24 μg ml⁻¹ with iodine, DDQ and TCNQ, respectively, with correlation coefficients not less than 0.9989. The proposed procedures could be applied successfully to the determination of the investigated drugs in vials, capsules, tablets and suspensions with good recovery; percent ranged 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 free energy changes using Benesi–Hildebrand plots were studied. The binding of cephalosporins to proteins in relation to their molar absorptivities was studied.