Determination of pefloxacin in serum and pharmaceutical forms by derivative spectrophotometry

A method for the direct determination of pefloxacin in serum and pharmaceutical forms (tablets and ampoules) has been developed, based on the use of second-order derivative ultraviolet spectra. Spectrophotometric assay of pefloxacin in tablets and ampoules was carried out in 0.1 mol/L NaOH, while in serum it was performed in 0.1 mol/L NaOH with the addition of sodium dodecylsulfate, in 337–347 nm wavelength range. Linear calibration curves were obtained in the concentration ranges 2–30g/mL pefloxacin for tablets and ampoules and 0.12–5 g/ mL for serum samples. Relative error of determination, as criterion for accuracy, was less than 1%, while the precision was better than 4 ng/ml. The minimum detectable concentration of pefloxacin in serum was 15 ng/mL.     

Determination of paracetamol in pharmaceutical formulations using a sequential injection system

A simple method for the rapid determination of paracetamol in pharmaceutical formulations is described. The method involves oxidation of paracetamol by potassium hexacyanoferrate(III) and a subsequent reaction with phenol in the presence of ammonia. The blue complex formed is measured at 630 nm. The system has a sample frequency of 27 samples per h with a detection limit of 0.2 mg l⁻¹. The calibration curve is linear up to 60 mg l⁻¹ with a relative standard deviation of 1.2% (n=10).     

Determination of attapulgite and nifuroxazide in pharmaceutical formulations by sequential digital derivative spectrophotometry

A new method for the sequential determination of attapulgite and nifuroxazide in pharmaceutical formulations by first- and second-derivative spectrophotometry, respectively, has been developed. In order to obtain the optimal conditions for nifuroxazide stability, studies of solvent, light, and temperature effects were performed. The results show that a previous hydrolysis of 2 h in 1.0 x 10(-1)M NaOH solution is necessary in order to obtain stable compounds for analytical purposes. Subsequently, the first- and second-derivative spectra were evaluated directly in the same samples. The sequential determination of the drugs can be performed using the zero-crossing method; the attapulgite determination was carried out using the first derivative at 278.0 nm and the nifuroxazide determination, using the second derivative at 282.0 nm. The determination ranges were 5.7 x 10(-6)-1.0 x 10(-4) and 3.7 x 10(-8) -1.2 x 10(-4)M for attapulgite and nifuroxazide, respectively. Repeatability (relative standard deviation) values of 1.2 and 3.0% were observed for attapulgite and nifuroxazide, respectively. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets. Further, infrared spectroscopy and cyclic voltammetry studies were carried out in order to obtain knowledge of the decomposition products of nifuroxazide.     

Simultaneous determination of propacetamol and paracetamol by derivative spectrophotometry

The present paper describes a procedure that phenols in air were preconcentrated in a membrane cell and their content was determined by adsorptive polarography. First, the phenols in air samples were preconcentrated in a membrane cell using 2.0 M NaOH solution, then in a pH 1.3 buffer solution p-bromophenylamine forms a diazoate with NaNO(2), and into the mixture the collected phenols were added to form azo-compound in a pH 13 buffer solution. The azo-compound can be adsorbed at the mercury electrode and yields a sensitive oscillopolarographic wave. Over the range 2.0x10(-8)-2.0x10(-5) M, the peak currents are linearly proportional to the concentration of phenols. The detection limit is 5.0x10(-9) M.     

Simultaneous determination of pseudoephedrine sulfate, dexbrompheniramine maleate and loratadine in pharmaceutical preparations using derivative spectrophotometry and ratio spectra derivative spectrophotometry

Two new spectrophotometric methods are described for the simultaneous analysis of pseudoephedrine sulfate-dexbrompheniramine maleate (DBP) and pseudoephedrine sulfate-loratadine combinations. In the first, derivative spectrophotometry, dA/dlambda values were read at zero-crossing points. In the second, ratio spectra derivative spectrophotometry, analytical signals were measured at the wavelengths corresponding to either maxima or minima for these drugs in the first derivative spectra of their ratio spectra. The procedures do not require any separation step. Mean recoveries were found to be >99% in the methods for these compounds in their synthetic mixtures. All the spectrophotometric methods proposed were compared with each other and HPLC which was also developed by us and applied to the pharmaceutical preparations selected.     

Simultaneous quantitative resolution of atorvastatin calcium and fenofibrate in pharmaceutical preparation by using derivative ratio spectrophotometry and chemometric calibrations.

In the present work, five different spectrophotometric techniques for simultaneous determination of formulations containing atorvastatin calcium (ATOR) and fenofibrate (FENO) in various combinations are described. In ratio spectra derivative spectrophotometry, analytical signals were measured at wavelengths corresponding to either maximums or minimums for both drugs in first derivative spectra of ratio spectra obtained by using either spectrum as divisor. For the remaining four methods using chemometric techniques, namely, classical least squares (CLS), inverse least squares (ILS), principal component regression (PCR) and partial least squares (PLS), the calibrations were constructed by using the absorption data matrix corresponding to the concentration data matrix, with measurements in the range of 231 - 310 nm (Deltalambda = 1 nm) in their zero-order spectra. The linearity range was found to be 4 - 22 and 2 - 20 microg/ml for ATOR and FENO, respectively. The validity of the proposed methods was successfully assessed for analyses of both drugs in laboratory-prepared mixtures and in commercial tablet formulations.     

Determination of platinum and iridium in reforming catalysts by second derivative and absorptiometric spectrophotometry

Summary Investigations on the spectrophotometric determination of platinum as a complex formed by tin(II)chloride in hydrochloric acid are reported. The determination of platinum was found to be interfered with by iridium, because it also forms a complex with tin(II) chloride. The features of the derivative absorption spectrophotometry for the quantitative determination of platinum and iridium was also studied. The analytical application of the method for the determination of platinum and iridium in catalysts was investigated.     

Determination of oxytetracycline and doxycycline in pharmaceutical compounds, urine and honey by derivative spectrophotometry

Derivative spectrophotometric methods have been developed for determining oxytetracycline and doxycycline and for resolving their binary mixtures. Oxytetracycline and doxycycline were determined in pharmaceutical samples, urine and honey without any pre-treatment of the samples. In all instances, first-derivative spectra were used.     

Simultaneous determination of copper and iron by second derivative spectrophotometry using mixtures of ligands

A highly sensitive and selective second derivative spectrophotometric method has been developed for the determination of copper and iron in mixtures. The method is based on the separation of the analytes by liquid-liquid extraction as picrate ion pairs. Iron-picrate, reacts in the organic phase of DCE with 5-phenyl-3-(4-phenyl-2-pyridinyl)-1,2,4-triazine (PPT). Similarly the copper-picrate reacts with 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline (bathocuproine). The extracts were evaluated directly by derivative spectrophotometric measurement, using the zero-crossing approach for determination of copper and graphic method for iron. Iron and copper were thus determined in the ranges 8-120 ng ml(-1) and 8-125 ng ml(-1), respectively, in the presence of one another. The detection limits achieved (3sigma) were 2.9 ng ml(-1) of iron and 2.8 ng ml(-1) of copper. The relative standard deviations were in all instances less than 2.1%. The proposed method was applied to the determination of both analytes in river and tap water and the results were consistent with those provided by the AAS standard method.     

Simultaneous determination of dapsone and pyrimethamine by derivative spectrophotometry in pharmaceutical formulations

A simple and fast method was developed for the simultaneous determination of dapsone and pyrimethamine by first-order digital derivative spectrophotometry. Acetonitrile was used as a solvent to extract the drugs from the pharmaceutical formulations, and the samples were subsequently evaluated directly by digital derivative spectrophotometry. The simultaneous determination of both drugs was performed by the zero-crossing method at 249.4 and 231.4 nm for dapsone and pyrimethamine, respectively. The best signal-to-noise ratio was obtained when the first derivative of the spectrum was used. The linear range of determination for the drugs was from 6.6 x 10(-7) to 2.0 x 10(-4) and from 2.5 x 10(-6) to 2.0 x 10(-4) mol/L for dapsone and pyrimethamine, respectively. The excipients of commercial pharmaceutical formulations did not interfere in the analysis. Chemical and spectral variables were optimized for determination of both analytes. A good level of repeatability, 0.6 and 1.7% for dapsone and pyrimethamine, respectively, was observed. The proposed method was applied for the simultaneous determination of both drugs in pharmaceutical formulations.     

Simultaneous determination of calcium and magnesium by derivative spectrophotometry in pharmaceutical products

First- and second-derivative spectrophotometric methods for the simultaneous determination of calcium and magnesium in their mixtures are described. The methods are based on the colored complexes formed by calcium and magnesium with bromopyrogallol red in presence of Tween 80 as a surfactant. The zero-crossing method has been utilized to measure the first- and second-derivative value of the derivative spectrum. Calcium (0.8-4.8microgml(-1)) is determined in the presence of magnesium (0.5-3.5microgml(-1)) at the pH 10 and vice versa at zero-crossing wavelengths of 544.5 and 570nm in the first-derivative procedure and 574 and 531nm in the second-derivative procedure, respectively. The detection limits achieved were 0.0575microgml(-1) of calcium and 0.03microgml(-1) of magnesium. The relative standard deviations were in all instances less than 2%. The proposed method has been applied to the simultaneous determination of calcium and magnesium in different samples: commercial multivitamin, human serum and drinking water where excellent agreement between reported and obtained results was achieved.     

Determination of trace amounts of beryllium using derivative spectrophotometry in non-ionic micellar medium

A rapid and sensitive method for the trace level determination of beryllium based on the formation of a 1:2 complex (λ_max 560 nm) with 1,4-dihydroxy-9,10-anthracenedione in an aqueous medium containing Triton X-100 is reported. Beer’s law is followed in the range 3.60–360 ng ml⁻¹ of Be(II). The molar absorptivity and Sandell’s sensitivity are 1.68×10⁴ l mol⁻¹cm⁻¹ and 0.54 ng cm⁻², respectively; detection limit is 0.23 ng ml⁻¹ of Be(II). Analysis of synthetic mixtures of composition similar to that of alloys and spiked samples of distilled water, gave results that are in agreement with their beryllium content.     

一阶导数紫外分光光度法测定羟甲基烟酰胺

研究了羟甲基烟酰胺在水、0.01mol·L-1NaOH和0.01mol·L-1HCl中的紫外吸收,通过对比,提出了以0.01mol·L-1NaOH为溶剂的一阶导数紫外分光光度法测定新方法。该法排除了赋型剂的影响,已用于片剂中羟甲基烟酰胺的测定。     

Simultaneous determination of N-butylscopolamine and oxazepam in pharmaceutical formulations by first-order digital derivative spectrophotometry

A simple method has been developed for the simultaneous determination of N-butylscopolamine bromide and oxazepam in pharmaceutical formulations using first-order digital derivative spectrophotometry. Acetonitrile was selected as the solvent in which both compounds showed well-defined bands. Both analytes showed good stability in this solvent when solutions of the analytes were exposed to light and temperatures between 20 degrees and 80 degrees C. The simultaneous determination of both drugs was performed by the zero-crossing method at 226.0 and 257.0 nm for N-butylscopolamine and oxazepam, respectively. The linear range of determination was found to be 2.5 x 10(-7) to 8.0 x 10(-5) mol/L for N-butylscopolamine and 7.1 x 10(-8) to 8.0 x 10(-5) mol/L for oxazepam. A very good level of repeatability (relative standard deviation) of 0.2% was observed for N-butylscopolamine and oxazepam. The ingredients commonly found in pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in pharmaceutical formulations (capsules).     

Spectrophotometric multicomponent analysis of a mixture of chlorhexidine hydrochloride and lidocaine hydrochloride in pharmaceutical formulation using derivative spectrophotometry and partial least-squares multivariate calibration

Two spectrophotometric methods were applied to the simultaneous assay of chlorhexidine hydrochloride (CHL) and lidocaine hydrochloride (LIH) in pharmaceutical formulations. Using derivative spectrophotometry, CHL was determined by measurement of its first derivative signal at 290 nm (peak to zero amplitude) in the concentration range 5–9 μg/mL, and LIH was analysed by measurement of its second derivative signals at 272 and 276 nm (peak to peak amplitude) in the concentration range 160–480 μg/mL. With the partial least-squares (PLS-2), the experimental calibration matrix was constructed using 9 samples. The concentration ranges considered were 5–7 μg/mL for CHL and 220, 240, 260 μg/mL for LIH. The absorbances were recorded between 240 and 310 nm at every 5 nm.     

Determination of tadalafil in pharmaceutical preparation by HPLC using monolithic silica column

The simple, reliable and reproducible HPLC and extraction methods were developed for the analysis of tadalafil in pharmaceutical preparation. The column used was monolithic silica column, Chromolith Performance RP-18e (100 mm × 4.6 mm, i.d.). The mobile phase used was phosphate buffer (100 mM, pH 3.0)-acetonitrile (80:20, v/v) at the flow rate of 5 mL min⁻¹ with UV detection at 230 nm at ambient temperature. Extraction of tadalafil from tablet was carried out using methanol. Linearity was observed in the concentration range from 100 to 5000 ng mL⁻¹ for tadalafil with a correlation coefficient (R²) 0.9999 and 100 ng mL⁻¹ as the limit of detection. The values of linearity range, correlation coefficient (R²) and limit of detection were 50-5000 ng mL⁻¹, 0.9999-50 ng mL⁻¹, respectively for sildenafil. Parameters of validation prove the precision of the method and its applicability for the determination of tadalafil in pharmaceutical tablet formulation. The method is suitable for high throughput analysis of the drug.     

Determination of sulphamethizole in the presence of nitrofurantoine by derivative spectrophotometry and ratio spectra derivative

Two methods for determining sulphamethizol in the presence of nitrofurantoine in mixtures by first-derivative spectrophotometry and by the first derivative of the ratio spectra are described. The procedures do not require any separation step. In the first method the measurements are obtained in the zero-crossing wavelengths and the calibration graphs were linear up to 32 mug/ml of sulphamethizole at 251 and 278.5 nm. In the second method, the calibration graphs were linear up to 43 mug/ml by measuring at the maximum (263 nm), at the minimum (244 nm) and peak to peak. The methods were applied for determining sulphamethizole in a pharmaceutical product containing nitrofurantoine.     

Determination of sulfamethoxazole and trimethoprim by ratio spectra derivative spectrophotometry

Summary A new method is described for analysing the binary mixture of sulfamethoxazole and trimethoprim, using the ratio spectra derivative spectrophotometry. The procedure does not require any separation step. Calibration graphs were linear up to 25 mg/l of sulfamethoxazole and up to 50 mg/l of trimethoprim; their 1:5 and 5:1 (m/m) mixtures can be resolved with recoveries between 97 and 104%. The method was satisfactorily applied for determining sulfamethoxazole and trimethoprim in different pharmaceutical products.     

Determination of Simvastatin in tablet formulations by derivative UV spectrophotometry

An investigation of UV spectroscopic methods, i.e. absorbance, 1st and 2nd derivative spectra for the determination of simvastatin in tablet formulations has been undertaken. This work investigated the possible difficulties that might arise due to the presence of UV absorbing excipients and likely presence of degradation products in such assays. We have demonstrated that the presence of ascorbic acid as an excipient causes interference with simple absorbance measurements leading to a gross over-determination of the simvastatin. 1st and 2nd derivative methods appear to eliminate this problem. We have also shown that the degradation product of simvastatin, i.e. simvastatin β-hydroxy acid, having an almost identical spectrum to the parent drug, may cause problems in the UV spectroscopic determination of the drug in degraded samples.