Spectrophotometric methods for determining meloxicam in pharmaceuticals using batch and flow-injection procedures.

Two sensitive and fast spectrophotometric methods using batch and flow-injection procedures for the determination of meloxicam (MX) are proposed. The methods are based on the formation of a green complex between this drug and Fe(III) [2MX/Fe(III)] in a methanolic medium. The calibration graphs resulting from measuring the absorbance at 570 nm are linear over the ranges 2.0-200 and 5.00-250 mg l(-1) with detection limits of 0.47 and 0.72 mg l(-1), respectively. Furthermore, a flow-injection spectrophotometric method involving measurement of the absorbance of the drug at 362 nm in 0.1 M NaOH is presented. The calibration graph is linear over the range 0.5-20 mg l(-1) with a detection limit of 0.04 mg l(-1). The methods are applied to the routine analysis of MX in pharmaceuticals.     

Fluorimetric determination of chloroxine using manual and flow-injection methods

A reliable and highly sensitive method is described for the determination of chloroxine in pharmaceutical preparations. It involves the formation of a complex between chloroxine and aluminum(III) in a micellar medium. The complex is a very fluorescent species, and there is a linear relationship between chloroxine concentration and fluorescence intensity over the range {ce:inline-formula}2.0 × 10 ⁻⁸ −5.1 × 10 ⁻⁵mol1 ⁻¹{/ce:inline-formula}. The limit of detection is {ce:inline-formula}5 × 10 ⁻⁹mol1 ⁻¹{/ce:inline-formula}. The method can be easily adapted to a flow system using a three-channel manifold, the peak height being proportional to the chloroxine concentration over the range {ce:inline-formula}5.6 × 10 ⁻⁷ − 5.6 × 10 ⁻⁵mol1 ⁻¹{/ce:inline-formula}. Manual and flow-injection procedures permit the determination of chloroxine in the presence of chlorquinaldol, and have been successfully applied to the determination of chloroxine in pharmaceutical preparations.     

Spectrophotometric determination of pefloxacin mesylate in pharmaceuticals

A spectrophotometric method is described for assay of pefloxacin mesylate (PFM) in bulk drug and in tablets. The method is based on back extraction of the bromophenol blue dye at pH 5.2 from the dye-drug ion pair followed by measurement of the dye absorbance at 590 nm. The working conditions of the method were investigated and optimized. Beer's law plot showed a good correlation in the concentration range of 0.15-1.25 microg mL(-1). Sensitivity indices such as molar absorptivity, limits of detection and quantification are reported. Intra-day and inter-day precision, and accuracy of the methods were established according to the ICH guidelines, and the er values were in the range of -1.7 to 1.8% with RSD values ranging from 1.0 to 1.1%. The method was successfully applied to the assay of PFM in tablet preparations with recoveries varying from 97.5 to 101.9%, with standard deviation in the range of 0.6 to 1.9. The results were statistically compared with those of the reference method by applying Student's t-test and F-test. Accuracy evaluated by means of the spike recovery method, range from 97.0 to 106.0%, with precision better than 3%.     

Recent applications of flow-injection and sequential-injection analysis techniques to chemiluminescence determination of pharmaceuticals

A review is presented on the state of the art of the chemiluminescence analysis of pharmaceuticals by the two most relevant automated controlled-flow methodologies--flow-injection analysis (FIA) and sequential-injection analysis (SIA). The current chemiluminometric applications of FIA and SIA in pharmaceutical analysis are discussed with special emphasis on the analytical figures of merit and sample matrix characteristics. The review involving 211 references and covering papers published between 2001 and 2006 is divided into several sections according to the fundamental types of chemiluminescence systems employed.     

Electrochemical behaviour and determination of acrivastine in pharmaceuticals and human urine

The differential pulse polarography, DC-tast polarography and cyclic voltammetry behaviour of acrivastine was studied in Britton-Robinson buffer solutions (pH 2-11.7). In acidic media, a non-reversible diffusion controlled reduction process involving four electrons takes place. Two reduction waves appear at a E(1/2)=-0.6 and -0.99 V. The reduction mechanism is discussed. The linear relationship between peak current height and acrivastine concentration allowed the differential pulse polarographic determination of acrivastine over a wide concentration range, from 0.35 to 26.1 mg l(-1)at pH 2.5. The procedure was applied to determination of the drug in pharmaceutical formulations and human urine samples.     

Optimized and validated spectrophotometric methods for the determination of raloxifene in pharmaceuticals using permanganate

Two simple and sensitive spectrophotometric methods are described for the determination of raloxifene hydrochloride (RLX) in pure form and in tablets. The first method (method A) is based on the formation of a yellowish-brown chromogen peaking at 430 nm when RLX was reacted with permanganate in acetic acid medium. In the second method (method B), RLX was reacted with a measured excess of permanganate in H₂SO₄ medium followed by the spectrophotometric measurement of the unreacted KMnO₄ at 550 nm. Under the optimized experimental conditions, Beer’s law is obeyed in the concentration range 0.6–6.0 and 1.5–15.0 μg mL⁻¹ with molar absorptivity of 7.01 × 10⁴ and 2.8 × 10⁴ L mol⁻¹ cm⁻¹ for method A and method B, respectively. The limits of detection (LOD) and quantification (LOQ) have also been reported. The intra-day and inter-day RSD and RE values at three different concentrations were assessed. The proposed methods were applied to the commercially available tablets, and the results were statistically compared with those of the reference method. The accuracy and reliability of the methods were further ascertained by recovery studies.     

Spectrophotometric determination of hydralazine with 2-hydroxy-1-naphthaldehyde in pharmaceuticals

A new extraction-spectrophotometric method for the determination of hydralazine, based on its reaction with 2-hydroxy-1-naphthaldehyde at 25 degrees C, is described. The calibration curve was linear between 0.4 and 6 mg/mL of hydralazine. The molar absorbtivity of the product at 408 nm is 40,900 L.mol-1.cm-1. The method described was applied to the analysis of hydralazine in pharmaceutical preparations containing reserpine, hydrochlorothiazide, bendrofluorthiazine, propranolol, and other substances. The agreement with the U.S.P. XXI method was satisfactory for tablets and injections, but not for pellets.     

Flow injection spectrophotometric determination of ofloxacin in pharmaceuticals and urine.

A sensitive and fast flow-injection spectrophotometric method for the determination of ofloxacin is proposed. The method is based on the formation of a yellow complex between ofloxacin and Fe (III), in sulphuric medium. The influence of FI and chemical variables were studied. The calibration graph resulting from measuring the absorbance at 420 nm is linear over the range 5.0 x 10(-6)8.0 x 10(-4)M (1.8-289 mg l(-1)) with a detection limit of 2.0 x 10(-6)M (0.72 mg l(-1)). The method is applied to the routine analysis of ofloxacin in pharmaceuticals and human urine.     

Spectrophotometric determination of cimetidine in the presence of its acid-induced degradation products

Cimetidine has been determined in the presence of its acid-induced degradation products using a second derivative (D2-) spectrophotometric method (method I) or a colorimetric method (method II). The former is based on D2-value measurement at 216 nm, whilst the latter depends on charge-transfer complexation with dichlorophenol-indophenol. The two methods are proved to be stability indicating, since plots of log C% versus time were linear. The application to cimetidine determination in tablets and ampoules gave good results.     

Spectrophotometric determination of labetalol in pharmaceutical preparations and spiked human urine

Two simple and sensitive spectrophotometric methods were developed for the spectrophotometric determination of labetaolol (LBT). Both methods are based on the phenolic nature of the drug. The first method (Method I) is based on coupling LBT with diazotized benzocaine in presence of trimethylamine. A yellow colour peaking at 410 nm was produced and its absorbance is linear with the concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.9993. The molar absorptivity was 2.633 x 10(4) l mol(-1) cm(-1). The second method (Method II) involves coupling LBT with diazotized p-nitroaniline in presence of sodium carbonate. An orange colour peaking at 456 nm was obtained and its absorbance is linear with concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.99935. The stoichiometry of the reaction in both cases was accomplished adopting the limiting logarithmic method and was found to be 1:1. The developed method could be successfully applied to commercial tablets. The results obtained were in good agreement with those obtained using the official methods. No interference was encountered from co-formulated drugs, such as hydrochlorothiazide. The method was further extended to the in-vitro determination of LBT in spiked human urine. The % recovery (n=4) were 97.7+/-5.75 and 103.27+/-5.42 using the Methods I and II, respectively.     

Tetracycline-selective electrode for content determination and dissolution studies of pharmaceuticals by flow-injection analysis (FIA)

The present work describes the construction and evaluation of different tetracycline (TC)-selective electrodes without inner reference solution and with polymer membranes. The several electrodes were prepared with poly(vinyl chloride) or ethylene(vinyl acetate) membranes comprising o-nitrophenyl octyl ether or bis(2-ethylhexyl)sebacate as mediator solvents and tetracycline tetrakis(4-clorophenyl)borate as ion exchanger. The best performance was recorded for the poly(vinyl chloride) membranes with bis(2-ethylhexyl)sebacate. Using solutions with adjusted ionic strength, this type of electrode presented a slope of 57.4 mV decade(-1) and a reproducibility of +/-0.3 mV day(-1), for an analytical range from 1.2 x 10(-4) to 1.0 x 10(-2) M. The pH working range was 2.0-3.8. Tubular-shaped potentiometric detectors based on the same selective membrane were also constructed. When TC solutions with adjusted ionic strength of concentrations ranging from 1.0 x 10(-4) to 1.0 x 10(-2) M were injected into a single-channel flow manifold, the detectors presented a slope of 56.6 mV decade(-1) and a reproducibility of +/-0.5 mV day(-1). The pH working range was 1.9-3.9. Both batch and flow procedures were applied to the potentiometric analysis of oral dosage forms. Average recoveries were within 98.6 to 100.3% and the t test indicated the accuracy of these results in comparison to an independent methodology. The flow system with the potentiometric detector was employed in dissolution studies as well.     

Spectrophotometric methods for the determination of sulphathiourea

Three simple and sensitive spectrophotometric methods are described for the determination of sulphathiourea. The methods are based on the interaction of this thioamide with either iodine, tetracyanoethylene (TCNE) or copper nitrate to give the corresponding charge-transfer or metal-ion complexes, which can be measured at 363, 350 and 353 nm, respectively. In each case, a 1:1 complex was formed. Beer's law is obeyed for each procedure in a concentration range of 1-150 micrograms ml-1. The proposed procedures can be applied to the determination of sulphathiourea in its pharmaceutical formulations.     

Determination of metoprolol tartrate in tablets and human urine using flow-injection chemiluminescence method

In this paper, a simple, rapid and sensitive flow-injection chemiluminescence method has been developed for the determination of metoprolol tartrate, which acts as a kind of sensitizer in the chemiluminescence emission from the redox of SO(3)(2-) with Ce(IV) in acidic medium. Under the optimized conditions, the proposed method allows the measurement of metoprolol tartrate over the range of 1.5 x 10(-8) to 7.3 x 10(-6)mol/L with a detection limit of 4.7 x 10(-9)mol/L (3sigma), and the relative standard deviation for 7.3 x 10(-7)mol/L metoprolol tartrate (n=11) is 2.20%. The utility of this method was demonstrated by determining metoprolol tartrate in tablets and human urine sample.     

Spectrophotometric studies and application of imipramine-eriochrome cyanine R system for determination of imipramine in pharmaceuticals

Eriochrome cyanine R (ECR) has been tested as reagent for the determination of imipramine. It reacts in neutral medium with imipramine forming reddish compound, which can be quantitatively extracted into n-butanol. This property has been successfully used for the extractive-spectrophotometric determination of imipramine. Beer's law is obeyed in concentration range of 10-80 microg ml(-1) of imipramine. The method was applied to the determination of imipramine in its pharmaceutical.     

Spectrophotometric determination of diaminopyrimidines using benzoquinone

The diaminopyrimidine derivatives trimethoprim (TMP), pyrimethamine (PMA) and 2,4-diaminopyrimidine (2,4-DAP) are found to react readily and efficiently in an aqueous solution with p-benzoquinone (p-BQ) to form a colored product with an absorption optimum wavelength of about 500 nm. The optimum reaction time, pH, temperature, solvent, and [p-BQ] are determined by separate trials. These conditions are confirmed by a MultiSimplex optimization method. The molar absorptivities of the TMP, PMA, and 2,4-DAP reaction products at 500 nm are 10,830, 10,650, and 9660 l mol(-1) cm(-1), respectively. TMP shows a linear range between 5 and 100 mg/l while PMA and 2,4-DAP exhibit linearity between 15 and 75 mg l(-1) and 5 and 30 mg l(-1), respectively. There is some specificity to this reaction; 2-aminopyrimidine does not react. Under the optimum conditions, sulfamethoxazole (SM) reacts rather poorly with a molar absorptivity of about 110 l mol(-) cm(-1). Using p-BQ, TMP in a pharmaceutical sample can be determined in the presence of SM using derivative spectrophotometry. The TMP-p-BQ reaction is adaptable for flow injection analysis.     

Voltammetric and flow amperometric methods for the determination of melatonin in pharmaceuticals

Melatonin can be sensitively detected in pharmaceuticals by two different and simple electrochemical methods: cyclic voltammetry (CV) and amperometric detection in a flow injection analysis system (FIA-ED). An adequate pre-treatment of the carbon paste electrode in the first case and the employ of a high flow rate in the second one were the key for obtaining a very good reproducibility (R.S.D. values of 1.5 (n=10) and 1.3% (n=20), respectively). Low limits of detection were achieved and with the coupling of a flow system a linear dynamic range of three orders of magnitude (from 10(-8) to 10(-5) M) was obtained. Both methods were applied to the determination of melatonin in pharmaceuticals. In order to best validate these methodologies a fluorescent procedure was developed to contrast the results. As no interferences from the matrix were found the employ of a separation technique is not necessary. In this way the procedure is fastened and simplified. Moreover, the low price, ease of handling, possibility of automation and high sample throughput are important advantages that convert the flow methodology in an attractive alternative for quality control of pharmaceuticals.     

New spectrophotometric methods for the quantitative determination of chloramphenicol in pharmaceuticals

Three new methods are proposed for the simple and sensitive spectrophotometric determination of chloramphenicol in pure form and in related pharmaceutical preparations. Two methods are based on the diazotization of reduced chloramphenicol, followed by coupling either with iminodibenzyl to give a violet colored product (λ_max = 590 nm) or with 3-aminophenol to produce an orange-red colored product (λ_max = 470 nm). The third method makes use of sodium molybdate and pyrocatechol as coupling agents to give a pale red colored product (λ_max = 490 nm). The proposed procedures are highly reproducible and the maximum relative standard deviation is 0.3 % for five determinations. The new methods have been applied to the determination of chloramphenicol in capsules and injection solutions, and the results compare favorably with the official method. Common auxiliary substances used as components of pharmaceutical preparations do not interfere with the proposed methods. Plausible reaction mechanisms are proposed. Published in Khimiko-Farmatsevticheskii Zhurnal, Vol. 40, No. 10, pp. 52–56, October, 2006.     

Spectrophotometric methods for the determination of gemifloxacin in pharmaceutical formulations

This paper describes two simple spectrophotometric methods for the determination of the antibiotic gemifloxacin mesylate (GFX) in pharmaceutical formulations. The first (A) is an indirect method in which oxidation of the drug with a known excess of cerium (IV) sulphate is followed by determination of the residual oxidant by adding excess methyl orange and measuring residual dye at 507 nm. The second (B) is a derivatisation method involving reaction of GFX with 1,2-naphthoquinone-4-sulphonate (NQS) in alkaline medium (pH 11) to form an orange-coloured product exhibiting maximum absorption (λ_max) at 411 nm. The methods were linear in the concentration ranges 2–9 and 5–30 μg/mL for methods A and B, respectively, with intra-day precision (as RSD) <1.5% for both. When applied to the determination of GFX in pharmaceutical tablets, the results were in good agreement with those obtained by capillary electrophoresis. The two methods are useful for routine analysis of GFX in quality control laboratories.