Flow-injection chemiluminescence determination of captopril using on-line electrogenerated silver(II) as the oxidant

Smartphone application for captopril determination in dosage forms and synthetic urine employing digital imaging

A simple, accurate, and low-cost analytical procedure for captopril determination through digital imaging is presented. The method relies on the spot test reaction between captopril and palladium (II) chloride, which produces a yellow and water-soluble complex with maximum absorption at 380 nm. A smartphone camera and a portable apparatus built for internal lighting control were put together to acquire digital images of reaction mixtures. Digital image processing through the RGB approach was used to establish a quantitative relationship between color intensity and captopril concentration. Under the most suitable operational and experimental conditions, an analytical curve was built monitoring the Blue channel within the concentration range of 3.12 × 10^-5 to 1.21 × 10^-3 mol L^-1. Limits of detection and quantification were equal to 8.06 × 10^-6 and 2.69 × 10^-5 mol L^-1, respectively. Recovery percentage in synthetic urine samples ranged from 97.1% to 102.9%. Results were compared with a reference method and no significant differences were detected at the 95% confidence level. The developed method presents budgetary and environmental advantages concerning the use of cheap and easy-handled devices and the consumption of very low volumes of reagent (800 μL per determination). It can be a useful analytical tool for laboratories with limited financial resources while abiding by green chemistry principles.

Laser induced thermal lens microscopy for highly sensitive determination of captopril

In this work, a combined flow injection-photo thermal lens microscopy (FI-PTLM) system was used for highly sensitive determination of captopril as an angiotensin-converting enzyme inhibitor. Captopril has no absorption in the visible range, but due to its thiol group could interact with gold nanoparticles (GNPs). GNPs, because of their surface plasmon resonance (SPR), have absorption in the visible range, but their interaction with a low concentration of captopril shows no effective change in UV-Vis spectrophotometry because their aggregation is slight. On the contrary, at the same condition, the PTLM with a visible light source enables sensitive measurement of this compound. The thiol group of captopril binds to the surface of GNPs and decreases the SPR. At the optimum condition in the focal volume of 2.68 fL (f=10^-15), the obtained range of linearity was 50-800 nM. The developed method was successfully applied for the determination of captopril in human serum and pharmaceutical samples.

Development of a new procedure for the determination of captopril in pharmaceutical formulations employing chemiluminescence and a multicommuted flow analysis approach

This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0-150.0 µmol/L (r = 0.997), a limit of detection (3σ) of 2.0 µmol/L, a sample throughput of 164 determinations per hour, reagent consumption of 9 µg luminol and 42 µg hypochlorite per determination and generation of 0.63 mL of waste. A relative standard deviation of 1% (n = 6) for a standard solution containing 80 µmol/L captopril was also obtained.

Utilization of oxidation reactions for the spectrophotometric determination of captopril using brominating agents

Three simple, accurate and sensitive methods (A-C) for the spectrophotometric assay of captopril (CPL) in bulk drug, in dosage forms and in the presence of its oxidative degradates have been described. The methods are based on the bromination of captopril with a solution of excess brominating mixture in hydrochloric acid medium. After bromination, the excess brominating mixture is followed by the estimation of surplus bromine by three different reaction schemes. In the first method (A), the determination of the residual bromine is based on its ability to bleach the indigo carmine dye and measuring the absorbance at 610 nm. Method B, involves treating the unreacted bromine with a measured excess of iron(II) and the remaining iron(II) is complexed with 1,10-phenanthroline and the increase in absorbance is measured at 510 nm. In method (C), the surplus bromine is treated with excess of iron(II) and the resulting iron(III) is complexed with thiocyanate and the absorbance is measured at 478 nm. In all the methods, the amount of bromine reacted corresponds to the drug content. The different experimental parameters affecting the development and stability of the color are carefully studied and optimized. Beer's law is valid within a concentration range of 0.4-6.0, 0.4-2.8 and 1.2-4.8 microg mL(-1) for methods A, B and C, respectively. The calculated apparent molar absorptivity was found to be 5.16x10(4), 9.95x10(4) and 1.74x10(5)L mol(-1) cm(-1), for methods A, B and C, respectively. Sandell's sensitivity, correlation coefficients, detection and quantification limits are also reported. No interference was observed from common additives found in pharmaceutical preparations. The proposed methods are successfully applied to the determination of CPL in the tablet formulations with mean recoveries of 99.94-100.11% and the results were statistically compared with those of a reference method by applying Student's t- and F-test.

A 4-methylumbelliferone-based fluorescent probe for the sensitive detection of captopril

A highly sensitive fluorogenic probe for captopril, 4-methylumbelliferyl-2, 4-dinitrobenzenesulfonate (4-MUDNBS), was designed and synthesized. 4-MUDNBS is a nonfluorescent compound and was synthesized via the one-step reaction of 4-methylumbelliferone (4-MU) with 2,4-dinitrobenzenesulfonyl chloride. Upon mixing with captopril in basic solution, the 2,4-dinitrobenzenesulfonyl group of 4-MUDNBS was efficiently removed and highly fluorescent 4-MU was released, hence leading to the dramatic fluorescence increase of the reaction solution. The fluorescence intensity is linear with captopril concentration in the range 3.0-500 ng mL(-1) with a detection limit of 2.2 ng mL(-1) (3sigma). The effect of substituents on the benzenesulfonyl moiety of the probe is discussed, and the presence of electronegative groups is favorable for the thiolate-induced cleavage reaction. The proposed method has been successfully applied to the captopril determination in pharmaceutical preparations.

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.

Enhanced plasmon resonance light scattering signals of colloidal gold resulted from its interactions with organic small molecules using captopril as an example

Gold nanoparticles are known for their plasmon resonance absorption (PRA) depending on their size. Our this investigation shows that plasma resonance light scattering (PRLS) signals in the corresponding PRA region could be measured using a common spectrofluorometer, and be enhanced when aggregation of gold nanoparticles occurs due to their interaction with organic small molecules (OSMs). Using captopril (Cap) as an example, we investigated the interactions of gold nanoparticles with OSMs in order to propose a general method of OSMs such as typical clinic organic drugs. In aqueous medium of pH 2.09, there are about 2.2 x 10(3) Cap molecules covalently binding to the surface of a 10-nm diameter gold nanoparticle through the thiol functional group of Cap, and thus forms a core-shell assembly of [(Au)(31000)]@[(Cap)(2200)], displaying strong enhanced PRLS signals in the PRA region of gold colloid. The PRLS intensities characterized at 553.0 nm were found to be proportional to the concentration of Cap over the range of 0.1-1.7 mg L(-1) with the determination limit (3sigma) of 32.0 microg L(-1). With that, Cap in pharmaceutical preparations could be determined with the recovery of 97.0-104.5% and R.S.D. of less than 2.4%.

Quantitative determination of captopril and prednisolone in tablets by FT-Raman spectroscopy

A procedure for the quantitative determination of captopril and prednisolone in commercial tablets based on partial least squares (PLS) and principal component regression (PCR) treatment of FT-Raman spectroscopic data is described. In the studied medicines active pharmaceutical ingredients (APIs) constitute 4.2-16.7% of the tablet mass. Results obtained from calibration models built using unnormalised spectra were compared with the values found when an internal standard was added to each sample and the spectra were normalised by its selected band intensity at maximum or integrated. To appraise the quality of the models the relative standard error of predictions (RSEPs) were calculated for calibration and testing data sets. For captopril determination these were 1.8-2.2% (2.1-2.3%) and 2.7-3.1% (2.7-3.6%), respectively for the different PLS (PCR) models. For prednisolone these errors amounted to 1.8-2.1% (2.6-3.5%) and 3.2-3.7% (3.7-5.9%), respectively. Three commercial preparations of captopril containing 12.5mg and one 25mg of API per tablet were quantified using developed models. Found captopril contents, calculated versus results of iodometric titration, was equal 99.2-101.2% (99.2-102.0%), for the different PLS (PCR) calibration models and the different preparations. Quantification of prednisolone tablets, declared content 5mg per tablet, on the basis of PLS (PCR) models gave API amount, calculated versus results of UV-vis method, in the 99.0-101.0% (98.0-102.0%) range.

Validation of simultaneous volumetric and spectrophotometric methods for the determination of captopril in pharmaceutical formulations

Simple, sensitive and economical simultaneous volumetric and spectrophotometric methods for the determination of captopril have been developed. The methods were based on the reaction of captopril with potassium iodate in HCl medium. Amaranth was used as indicator to detect the end-point of the titration in aqueous layer. The iodine formed during the titration was extracted into CCl4 and subsequently determined spectrophotometrically at 510 nm. The Beer's law was obeyed in the concentration range of 120-520 microg ml-1. Rigorous statistical analyses were performed for the validation of the proposed methods. The proposed methods were successfully applied to the determination of captopril in dosage forms. Comparison of the means of the proposed procedures with those of reference methods using point and interval hypothesis tests showed no statistically significant difference.