Spectrophotometric determination of metronidazole and tinidazole in pharmaceutical preparations

Overview of Analytical Methods for Evaluating Tinidazole

BACKGROUND

Tinidazole (TIN) has amoebicidal, giardicidal, antifungal, and antimicrobial activities. It is marketed in the form of tablets. Analytical methods to assess the quality of TIN-based products are essential for correct pharmacotherapy.

OBJECTIVE

The objective of this review is to show an overview of the existing analytical methods for evaluating TIN, according to the quality control (QC) analysis routine and green analytical chemistry (GAC).

RESULTS

Official compendia show a method for evaluating TIN in tablets by nonaqueous titration, which has limitations (materials on the mg scale using solvents considered not recommended and harmful). The literature shows some analytical methods for evaluating TIN, both physicochemical and microbiological. The most used physicochemical method is UV (41%), and second is HPLC (28%). Among the microbiological methods, agar diffusion and turbidimetric methods are equally divided. The most studied matrix is TIN tablets (73%), and the most used solvent is methanol.

CONCLUSIONS

The literature shows space for the development of analytical methods according to GAC for evaluating TIN, optimizing time, resources, and materials, reducing waste generation, and opting for less aggressive reagents, solvents, and diluents.

HIGHLIGHTS

This review shows the status of analytical methods, both physicochemical and microbiological, for the analysis of TIN in pharmaceutical matrix, in the context of routine analysis of the chemical-pharmaceutical industries and of GAC.

Spectrophotometric determination of Metronidazole antibacterial drug via oxidation with alkaline potassium permanganate

Highly simple, sensitive and selective method is developed for the spectrophotometric determination of Metronidazole (MDZ) antibacterial drug either in pure form or in pharmaceutical formulations. This method is based on reduction of potassium permanganate by Metronidazole drug in sodium hydroxide solution to give green manganate ion which recorded at 610 nm. The method produced linear responses in the concentration range 4.28 - 59.91 µg mL^-1 with limit of detection (LOD) and limit of quantification (LOQ) 0.21 and 0.69 µg mL^-1 for Metronidazole drug respectively. The apparent molar absorptivity is 0.865 × 10⁴ L mol^-1 cm^-1, Sandell sensitivity is 0.019 µg cm^-2 and correlation coefficient is 0.951. The method is highly reproducible and has been applied to a wide variety of pharmaceutical formulations and the results compare favourably with those of official methods.

Heterostructured bismuth oxide/hexagonal-boron nitride nanocomposite: A disposable electrochemical sensor for detection of flutamide

Aquatic contamination from the accumulation of pharmaceuticals has induced severe toxicological impact to the ecological environment, especially from non-steroidal anti-inflammatory drugs (NSAIDs). Real-time monitoring of flutamide, which is a class of NSAIDs, is very significant in environmental protection. In this work, we have synthesized the hexagonal-h boron nitride decorated on bismuth oxide (Bi₂O₃/h-BN) based nanocomposite for the effective electrochemical detection of flutamide (FTM). The structural and morphological information of the heterostructured Bi₂O₃/h-BN nanocomposite was analyzed by using a sequence of characterization methods. Voltammetric techniques were used to evaluate the analytical performance of the Bi₂O₃/h-BN modified screen-printed carbon electrode (SPCE) for the FTM detection. The Bi₂O₃/h-BN modified SPCE displays a synergetic catalytic effect for the reduction of FTM due to large surface area, numerous active sites, fast charge transfer and abundant defects. The proposed electrochemical sensing platform demonstrates high selectivity, low detection limit (9.0 nM), good linear ranges (0.04-87 μM) and short response time for the detection of FTM. The feasibility of the electrochemical sensor has been proved by the successful application to determine FTM in environmental samples.

Partial least squares and linear support vector regression chemometric models for analysis of Norfloxacin and Tinidazole with Tinidazole impurity

The aim of the presented work is to compare two popular chemometric methods which are partial least squares regression (PLSR) and support vector regression (SVR). The comparison shows their characteristics via application of the suggested methods to analysis of Norfloxacin (NF) and Tinidazole (TZ) with the presence of a potential impurity of Tinidazole; 2-Methyl-5-nitro-1H-imidazole (MNZ). For appropriate analysis, a 3 factor 4 level experimental design was constructed, which results in a training set composed of 16 mixtures which contains different concentrations of the three components; achieving symmetry, rotatability and orthogonality in mixture space. In order to validate the prediction ability of the suggested models, an independent test set consisting of 8 in-space and 8 out-of-space mixtures was used. The presented results show high specificity and accuracy of the mentioned multivariate calibration models for analysis of in-space samples of NF and TZ in presence of (MNZ) using UV spectral data. Statistical comparisons of predictive abilities of proposed models against classical least squares CLS model and against each other was performed; whether for analysis of test set mixtures or dosage form. CLS model showed lower predictive ability compared to other models. Results obtained by SVR model are as accurate as PLSR model, however, optimization and implementation of PLSR is faster and easier, hence PLSR could be of choice for this given case study. The developed chemometric models were validated as directed by ICH strategies. The validated methods were efficiently used for estimation of NF and TZ in pure powders and pharmaceuticals which indicates their suitability for application in quality control examination of both of the drugs.

Evaluation of assay and in-vitro dissolution profile of certain fixed-dose combination using green analytical method

OBJECTIVES

The pharmaceutical industry and the National Regulatory Authorities (NRAs) are now focusing on the dissolution of multi-component drugs for quality control testing and predicting in vivo results to further consolidation of the biowaiver concept. The mixed formulation of Ciprofloxacin hydrochloride (CIP) and Metronidazole (MET) have been used as a model for simultaneous determination and obtaining in vitro dissolution profiles by using green analysis method namely (UV-CWT_(Db4, _a=490)).

MATERIAL AND METHODS

The proposed method (UV-CWT_(Db4, _a=490)) includes UV detection combined with Continuous Wavelet Transform (CWT) with Daubechies family and the order of fourth at the scaling factor (a=490) has been used and validated for analyzing and obtaining the dissolution profiles of the fixed-dose combination (CIP-MET).

RESULTS

The proposed method (UV-CWT_(Db4, _a=490)) has been validated effectively in accordance with ICH rules, regarding linearity, specificity, rigor, and preciseness of the working range (3.0-16.0μg/mL) for both (CIP) and (MET), respectively. As well as figures of merit were concluded. The dissolution profiles of CIP-MET tablets were acquired by the proposed (UV-CWT _(Db4, _a=490)) and HPLC reported methods were conveniently compared using the indicators f₁ and f₂ ("difference" and "similarity") the results ensured that there were no statistically differences between the methods. In addition, the green assessment tool, namely analytical eco-scale, evaluated and compared the greenness of the suggested method (UV-CWT_(Db4, _a=490)) and HPLC reported one.

CONCLUSION

The suggested process (UV-CWT_(Db4, _a=490)) was considered as an excellent green, rapid, accurate, economical and minimum-steps method for simultaneously resolve and construct the dissolution curves of a fixed-dose combination drug (CIP-MET) in a short time and without the use of organic solvents, enabling significant labor and resource savings.

Direct nano-electrospray ionization tandem mass spectrometry for the quantification and identification of metronidazole in its dosage form and human urine

A rapid, sensitive and direct nano-electrospray ionization-tandem mass spectrometry (NS-ESI-MS/MS) method, using an offline nanospray (NS) capillary, has been developed and validated for the analysis of metronidazole (MTZ). A mixture of 2 µl MTZ sample solution prepared in an ionization solvent consisting of methanol : water : formic acid in a ratio of 80 : 20 : 0.3, together with 2 µl of an internal standard (IS), 1,3,6-polytyrosine, is loaded into the back of the NS capillary. The NS capillary was fitted into the ion source at a distance of 3 mm between the NS tip and MS orifice. The sample is then analysed and acquired a sustainable signal that allowed for data compilation across various data points for MTZ identification and quantification. The quantification relied on the ratio of the [M + H]+ peaks of MTZ and IS with m/z values of 172.0717 and 182.0812, respectively, while the identification relied on the MS/MS of the precursor ions [M + H]+ of both compounds and their fragments at 128.05 for MTZ and 165.1 and 136.07 for the IS. The NS-ESI-MS/MS method was accurate and precise for the quantification of MTZ over the concentration range from 2.5 to 25 000 ng ml-1. The applicability of the method was confirmed by MTZ analysis in its pharmaceutical dosage form and detection of the analyte in clinical human urine samples without any sample treatment procedure.

Carbon quantum dots as a fluorophore for “inner filter effect” detection of metronidazole in pharmaceutical preparations

With houttuynia cordata as carbon source, photoluminescent carbon quantum dots (CDs) were obtained via a one-step hydrothermal procedure. The absorption band of metronidazole (MNZ, maximum absorption wavelength at 319 nm) can well overlap with the excitation bands of CDs (maximum excitation wavelength at 320 nm). A fluorescent approach has been developed for detection of MNZ based on the inner filter effect (IFE), in which as-prepared CDs act as an IFE fluorophore and the MNZ as an IFE absorber. We have investigated the mechanism of quenching the fluorescence of CDs and found that the IFE leads to an exponential decay in fluorescence intensity of CDs with increasing concentration of MNZ, but showed a good linear relationship (R² = 0.9930) between ln(F₀/F) with the concentration of MNZ in the range of 3.3 × 10⁻⁶ to 2.4 × 10⁻⁴ mol L⁻¹. Due to the absence of surface modification of the CDs or establishing any covalent linking between the absorber (MNZ) and the fluorophore (CDs), the developed method is simple, rapid, low-cost and less time-consuming. Meanwhile, it possesses a higher sensitivity, wider linear range, and satisfactory selectivity and has potential application for detection of MNZ in pharmaceutical preparations.

CDs were prepared using Houttuynia cordata via hydrothermal process, the absorption band of MNZ can well overlap the excitation bands of CDs, a simple, rapid approach for detection of MNZ was established on the basis of IFE.

HPTLC method for Simultaneous Determination of Norfloxacin and Tinidazole in presence of Tinidazole Impurity

Sensitive, selective and accurate high-performance thin layer chromatographic HPTLC method for quantitative determination of Norfloxacin (NF), Tinidazole (TZ) and 2-Methyl-5-nitroimidazole (MNZ) as potential impurity of Tinidazole is developed and validated in the presented work. Calibration curves were linear over the concentration ranges of 0.4-2.4, 0.4-1.6, 0.2-1.2 μg/band for NF, TZ and MNZ, respectively. The method depends on separation and quantitation of NF, TZ and MNZ on aluminium plates pre-coated with silica gel HPTLC 60F254 as stationary-phase using chloroform: methanol: formic acid (7.5:1: 0.3, by volume) as developing system followed by densitometric measurement of bands at 298 nm. The developed method was validated and proved to meet the requirements delineated by ICH guidelines with respect to linearity, accuracy, precision, specificity and robustness. The validated method was successfully applied for determination of studied drugs in bulk powders and in their pharmaceutical formulation indicating the ability of proposed method to be used for routine quality control analysis of these drugs.

Selective and validated kinetic spectrophotometric method for the determination of irbesartan in pure and pharmaceutical formulations

A novel-coupling reagent is used for the simple and sensitive kinetic spectrophotometric determination of irbesartan (IRB) in pure or pharmaceutical formulations. The method utilizes an oxidative coupling reaction based on oxidation of 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH) with Ce(IV) in 2% sulfuric acid medium, followed by coupling the produced electrophilic intermediate (diazonium salt of the reagent) with IRB to give greenish-blue colored product (1:1, stoichiometry) having maximum absorption at 629nm and the colored species is stable for more than 1h. The initial rate and fixed time (at 35min) methods are adopted for determination of IRB concentration. The linearity is in the ranges of 5.0-40.0μg/mL and 2.0-45.0μg/mL and the limit of detection is 0.46 and 0.40μg/mL for initial rate and fixed time methods, respectively. Molar absorptivity for the method was found to be 1.50×10⁴L/molcm. The validated kinetic methods can be successfully applied to the analysis of IRB in bulk and tablet dosage form and in the routine quality control analysis. The percentage recoveries were above 100% for both methods. The excipients did not interfere in the analysis.

Synthesis and Evaluation of a Molecularly Imprinted Polymer for the Determination of Metronidazole in Water Samples

A molecularly imprinted polymer was developed and evaluated for selective determination of metronidazole (MNZ) in wastewater. This was achieved by using sodium methacrylate as monomer, toluene as porogen, ethylene glycol dimethacrylate as crosslinker, azobisisobutyronitrile as initiator and metronidazole as template molecule to generate the selectivity of the polymer for the compound, as well as non-imprinted polymers were synthesized. Two different polymerization approaches were used, bulk and emulsion and the polymers obtained by emulsion presented higher retention percentages the MIP 2-M presented the higher retention (83%). The performed method, was validated in fortified water, showing linearity from 10 up to 1000 ng/mL; limit of detection and quantification for compound were between 3 and 10 ng/mL, respectively. Finally, the method was applied in samples of a wastewater treatment plant in the city of San Luis Potosí, México, and the concentrations of MNZ in these samples were 84.1-114 ng/mL.

Development and validation of sensitive kinetic spectrophotometric method for the determination of moxifloxacin antibiotic in pure and commercial tablets

New, accurate, sensitive and reliable kinetic spectrophotometric method for the assay of moxifloxacin hydrochloride (MOXF) in pure form and pharmaceutical formulations has been developed. The method involves the oxidative coupling reaction of MOXF with 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH) in the presence of Ce(IV) in an acidic medium to form colored product with lambda max at 623 and 660 nm. The reaction is followed spectrophotometrically by measuring the increase in absorbance at 623 nm as a function of time. The initial rate and fixed time methods were adopted for constructing the calibration curves. The linearity range was found to be 1.89-40.0 μg mL(-1) for initial rate and fixed time methods. The limit of detection for initial rate and fixed time methods is 0.644 and 0.043 μg mL(-1), respectively. Molar absorptivity for the method was found to be 0.89×10(4) L mol(-1) cm(-1). Statistical treatment of the experimental results indicates that the methods are precise and accurate. The proposed method has been applied successfully for the estimation of moxifloxacin hydrochloride in tablet dosage form with no interference from the excipients. The results are compared with the official method.

Synthesis of metronidazole-imprinted molecularly imprinted polymers by distillation precipitation polymerization and their use as a solid-phase adsorbent and chromatographic filler

Metronidazole-imprinted polymers with superior recognition properties were prepared by a novel strategy called distillation-precipitation polymerization. The as-obtained polymers were characterized by Fourier-transform infrared spectroscopy, laser particle size determination and scanning electron microscopy, and their binding performances were evaluated in detail by static, kinetic and dynamic rebinding tests, and Scatchard analysis. The results showed that when the fraction of the monomers was 5 vol% in the whole reaction system, the prepared polymers afforded good morphology, monodispersity, and high adsorption capacity and excellent selectivity to the target molecule, metronidazole. The optimal binding performance is 12.41 mg/g for metronidazole just before leakage occurred and 38.51 mg/g at saturation in dynamic rebinding tests. Metronidazole-imprinted polymers were further applied as packing agents in solid-phase extraction and as chromatographic filler, both of which served for the detection of metronidazole in fish tissue. The results illustrated the recoveries of spiked samples ranged from 82.97 to 87.83% by using molecularly imprinted solid-phase extraction combined with a C18 commercial column and 93.7 to 101.2% by directly using the polymer-packed chromatographic column. The relative standard deviation of both methods was less than 6%.

A simple reagent-free spectrophotometric assay for monitoring metronidazole therapy in aquarium water

A reagent-free spectrophotometric assay was developed to measure the concentration of metronidazole (a 5-nitroimidazole) in both freshwater and seawater matrices. This assay is simple, repeatable, sensitive, and precise and is ideal for use when a rapid, selective test to determine metronidazole concentration in aqueous matrices is necessary. The assay was practically tested on a South American fishes display during treatment with metronidazole for an outbreak of the flagellated parasite Spironucleus in a mixed cichlid (family Cichlidae) and tetra (family Characidae) community. The assay clearly illustrated the course of treatment for the system during a real clinical application. The assay is not without limitations, as interferences can occur from other drugs in the matrix with similar absorbance spectra. Nonetheless, this type of assay illustrates the potential for use of native absorbance assays in aqueous matrices for this and other therapeutic compounds.

Comparative study of novel spectrophotometric methods manipulating ratio spectra: an application on pharmaceutical ternary mixture of omeprazole, tinidazole and clarithromycin

Three simple, specific, accurate and precise spectrophotometric methods manipulating ratio spectra are developed for simultaneous determination of omeprazole (OM), tinidazole (TN) and clarithromycin (CL) in tablets. Method A, is an extended ratio subtraction one (EXRSM). Method B is a ratio difference spectrophotometric one (RDSM), while method C is mean centering of ratio spectra (MCR). The calibration curves are linear over the concentration range of 1-20 μg/mL, 10-60 μg/mL and 0.25-1.0 mg/mL for OM, TN and CL, respectively. The specificity of the developed methods is investigated by analyzing laboratory prepared mixtures of the three drugs and their combined dosage form. Standard deviation values are less than 1.5 in the assay of raw materials and tablets. The three methods are validated as per ICH guidelines and accuracy, precision, repeatability and robustness are found to be within the acceptable limits.

A new approach to the spectrophotometric determination of metronidazole and tinidazole using p-dimethylaminobenzaldehyde

A new approach to the spectrophotometric determination of metronidazole (MZ) and tinidazole (TZ) has been developed. The procedure involves coupling of diazotized nitroimidazoles with p-dimethylaminobenzaldehyde (DMAB) to form a greenish-yellow solution. Optimal temperature and time were 0 degrees C (iced) and 3 minutes for diazotization and 30 degrees C and 2 minutes for coupling for both MZ and TZ. Coloured adducts of MZ and TZ showed shoulders at 406 nm and 404 nm, respectively, which were selected as analytical wavelengths. The reaction with p-DMAB occurred in a 1:1 mole ratio. Beer's law was obeyed within the 4.8-76.8 microg mL(-1) concentration range with low limits of detection. The azo adducts were stable for over a week. Molar absorptivities were 1.10 x 10(3) (MZ) and 1.30 x 10(3) L mol(-1) cm(-1) (TZ). Overall recoveries of MZ and TZ from quality control samples were 103.2 + or - 1.3 and 101.9 + or - 1.3% over three days. There was no interference from commonly utilized tablet excipients. No significant difference was obtained between the results of the new method and the BP titrimetric procedures. The azo approach using the p-dimethylaminobenzaldehyde procedure described in this paper is simple, fast, accurate and precise. It is the first application of DMAB as a coupling component in the diazo coupling reaction.

Ion mobility spectrometry as a detector for molecular imprinted polymer separation and metronidazole determination in pharmaceutical and human serum samples

Application of ion mobility spectrometry (IMS) as the detection technique for a separation method based on molecular imprinted polymer (MIP) was investigated and evaluated for the first time. On the basis of the results obtained in this work, the MIP-IMS system can be used as a powerful technique for separation, preconcentration, and detection of the metronidazole drug in pharmaceutical and human serum samples. The method is exhaustively validated in terms of sensitivity, selectivity, recovery, reproducibility, and column capacity. The linear dynamic range of 0.05-70.00 microg/mL was obtained for the determination of metronidazole with IMS. The recovery of analyzed drug was calculated to be above 89%, and the relative standard deviation (RSD) was lower than 6% for all experiments. Various real samples were analyzed with the coupled techniques, and the results obtained revealed the efficient cleanup of the samples using MIP separation before the analysis by IMS as a detection technique.

Stability Indicating Methods for the Determination of Norfloxacin in Mixture with Tinidazole

Three stability indicating assay methods are developed for the determination of norfloxacin (Nor) in the presence of its decarboxylated degradation product and in mixture with tinidazole (Tnd). The proposed methods are reversed phase ion pair liquid chromatography (LC), thin layer densitometry (TLC) and second derivative ratio spectra zero crossing spectrophotometry ((2)DD). Chromatographic separation was achieved on mu-Bondapack C18 column 5 microm (300 mm x 3.9 mm, I.D.) and precoated silica gel TLC stationary phases for LC and TLC methods, respectively. Mobile phases consisting of phosphate buffer pH 3.2 : methanol (3 : 1, v/v) containing 0.005 M pentane sulfonic acid sodium salt and isopropanol : butanol : concentrated ammonia : water (25 : 50 : 5 : 25, v/v/v/v) were used for resolution of Nor and Tnd by both techniques, respectively. Detection was carried at 280 nm. In the ratio spectra method, detection of Nor was carried at 282 nm. Linearity, accuracy and precision were found to be acceptable over concentration ranges of 20-225 microg/ml, 0.8-4 microg/spot and 1-7 microg/ml for Nor by LC, TLC and (2)DD methods and over concentration ranges of 37.5-375 microg/ml and 4.8-20 microg/spot for Tnd by LC and TLC methods respectively. The suggested methods were successfully applied for the determination of both drugs in bulk powder, laboratory prepared mixtures and in commercial samples. Statistical comparison between the results obtained by the proposed and the reference methods was carried out using Student t-test, F ratio and one way ANOVA.

The application of resonance light scattering technique for the determination of tinidazole in drugs

A resonance light scattering technique to determine tinidazole in drugs was developed by tetraphenylboron sodium (TPB). Tinidazole was found to bind B(C(6)H(5))(-) (4) anion and transformed to tinidazole-TPB aggregate which displayed intense resonance scattering light. Effects of factors such as wavelength, acidity, stabilizers, and interferents on the RLS of tinidazole TPB were investigated in detail. The RLS intensity of the tinidazole-TPB suspension was obtained in sulfuric acid solution (pH = 1.44). The resonance scattering light intensity at the maximum RLS peak of 569.5 nm was linear to the concentration of tinidazole in the range of 10.0-30.0 mug mL(-1) with a detection limit of 5.0 mug mL(-1). Good results were also obtained with the recovery range of 95.13-106.76%. The method was applied to determine tinidazole in injections and tablets, showing high sensitivity and accuracy compared with the high performance liquid chromatography method (HPLC) according to Chinese Pharmacopoeia.

Application of nuclear magnetic resonance spectroscopy for quantitative analysis of miconazole, metronidazole and sulfamethoxazole in pharmaceutical and urine samples

Specific, accurate and precise NMR methods were developed for determining miconazole, metronidazole and sulfamethoxazole antibiotic drugs in authentic, pharmaceutical and urine samples. Proton nuclear magnetic resonance spectroscopy (1H NMR) with maleic acid as an internal standard and DMSO-d6 as NMR solvent were used. 1H NMR signals at 9.0, 8.06, 7.50 and 6.26 ppm corresponding to miconazole, metronidazole, sulfamethoxazole and maleic acid were respectively used for calculating the concentrations of drugs per unit dose. Average percent recoveries of (97.54-101.10), (98.06-100.46) and (97.83-102.83) with average uncertainties of 1.02, 0.45 and 0.86 were respectively obtained for determining authentic samples of miconazole, metronidazole and sulfamethoxazole in the concentration range of 0.92-170 mg/0.6 ml DMSO-d6. In pharmaceutical formulations and urine samples, average percent recoveries in the ranges of 97.50-101.33 and 94.46-100.86 were respectively obtained. Relative standard deviations (R.S.D.)<or=2.68 were obtained for analyzing the three drugs in authentic, pharmaceutical and urine samples. Admixtures of the three drugs in authentic, pharmaceutical and urine samples were analyzed. Good precisions (0.79-2.99%) and recoveries (93.40-104.97%) were obtained indicating the high selectivity and resolving power of the developed NMR methods and no needs for separation steps. Applying statistical Student t-test revealed insignificant difference between the real and measured contents at the 95% confidence level. F-test revealed insignificant difference in precisions between the developed NMR methods and HPLC methods reported for analyzing miconazole, metronidazole and sulfamethoxazole.

Spectrophotometric determination of oxiconazole in topical lotion using methyl orange

A spectrophotometric method is described for the determination of oxiconazole in raw material and in topical lotion. This method is based on the reaction of the oxiconazole with methyl orange in buffered aqueous solution of citric acid at pH 2.3. The chromogen, being extractable with dichloromethane, could be measured quantitatively with maximum absorption at 427 nm. The Lambert-Beer law was obeyed in the concentration range of 4.0-14.0 microg ml(-1). A prospective validation of the method showed that the method was linear (r=0.9995), precise (intra-day: CV=1.57% and inter-day: CV=1.50%) and accurate (mean recoveries: 99.69%). The results compared favourably with those of the HPLC method.

Spectrophotometric determination of metronidazole and secnidazole in pharmaceutical preparations

A rapid and sensitive spectrophotometric method is proposed for determination of metronidazole and secnidazole. The method depends on the reduction of metronidazole and secnidazole molecule with zinc dust and hydrochloric acid flowed by diazotization and coupling with 8-quinolinol to give red colored chromogens easily measured spectrophotometrically which has lambda(max) = 500 nm. The experimental conditions were optimized and Berr's law was obeyed over the applicable concentration ranges both techniques were applied successfully to a wide variety of pharmaceutical preparations.

Voltammetric Determination of Tinidazole Using a Glassy Carbon Electrode Modified with Single-Wall Carbon Nanotubes

An electrochemical method based on a single-wall carbon nanotubes (SWNTs) film-coated glassy carbon electrode (GCE) was described for the determination of tinidazole. In a 0.1 M Britton-Robinson buffer with a pH of 10.0, tinidazole yields a very sensitive and well-defined reduction peak at -0.78 V (vs. SCE) on a SWNTs-modified GCE. Compared with that on a bare GCE, the reduction peak of tinidazole increases significantly on the modified GCE. Thus, all of the experimental parameters were optimized and a sensitive voltammetric method is proposed for tinidazole determination. It is found that the reduction peak current is proportional to the concentration of tinidazole over the range from 5 x 10(-8) to 4 x 10(-5) M, and that the detection limit is 1 x 10(-8) M at 3 min open-circuit accumulation. This new analysis method was demonstrated with tinidazole drugs.

3-Aminophenol as a novel coupling agent for the spectrophotometric determination of sulfonamide derivatives

A rapid, simple and sensitive spectrophotometric method for the determination of some sulfa drugs is described. The method is based on the formation of orange yellow colored azo product by the diazotization of sulfonamides, viz., dapsone (DAP), sulfathiazole (SFT), sulfadiazine (SFD), sulfacetamide (SFA), sulfamethoxazole (SFMx), sulfamerazine (SFMr), sulfaguanidine (SFG) and sulfadimidine (SFDd) followed by a coupling reaction with 3-aminophenol in aqueous medium. Absorbance of the resulting orange yellow product is measured at 460 nm and is stable for 6 days at 27 degrees C. Beer's law is obeyed in the concentration range of 0.05-8.0 microg/ml 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. Plausible reaction mechanism is proposed for the formation of the azo product.

Highly sensitive reaction of tryptophan with p-phenylenediamine

A simple and sensitive spectrophotometric method for the determination of tryptophan (TRP) is described. The method is based on the coupling reaction of tryptophan with diazotized p-phenylenediamine dihydrochloride (PPDD) in sulfuric acid medium to give the colored product having an absorption maximum at 520 nm. The coupled product was stable for 2h. Beer's law is obeyed in the tryptophan concentration range of 0.25-11 microg/ml. The method is applied for the analysis of pharmaceutical preparations of tryptophan and also in protein samples for tryptophan. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed method and the significant feature of the method is that most of the amino acids do not interfere in the determination of tryptophan.