STABILITY-INDICATING HPLC METHOD FOR SIMULTANEOUS DETERMINATION OF CAPTOPRIL, INDAPAMIDE, AND THEIR RELATED COMPOUNDS

Development of a "turn off" fluorescent molecularly imprinted nanoparticle-based sensor for selective captopril quantification in synthetic urine and wastewater samples

The combination of silica nanoparticles with fluorescent molecularly imprinted polymers (Si-FMIPs) prepared by a one-pot sol-gel synthesis method to act as chemical sensors for the selective and sensitive determination of captopril is described. Several analytical parameters were optimized, including reagent ratio, solvent, concentration of Si-FMIP solutions, and contact time. Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and the ninhydrin assay were used for characterization. The selectivity was evaluated against molecules belonging to other drug classes, such as fluoroquinolones, nonacid nonopioids, benzothiadiazine, alpha amino acids, and nitroimidazoles. Under optimized conditions, the Si-FMIP-based sensor exhibited a working range of 1-15 µM, with a limit of detection (LOD) of 0.7 µM, repeatability of 6.4% (n = 10), and suitable recovery values at three concentration levels (98.5% (1.5 µM), 99.9% (3.5 µM), and 99.2% (7.5 µM)) for wastewater samples. The sensor provided a working range of 0.5-15 µM for synthetic urine samples, with an LOD of 0.4 µM and a repeatability of 7.4% (n = 10) and recovery values of 93.7%, 92.9%, and 98.0% for 1.0 µM, 3.5 µM, and 10 µM, respectively. In conclusion, our single-vessel synthesis approach for Si-FMIPs proved to be highly effective for the selective determination of captopril in wastewater and synthetic urine samples.

Green innovative fluorescence approach for the feasible and reliable assay of thiol-containing drugs; captopril as a model

In the present study, a novel spectrofluorimetric approach was designed for the analysis of captopril as a thiol-containing compound. The approach is based on the formation of a ternary fluorescent compound between the target thiol compound, ortho-phthaldehyde, and a suitable primary amine-containing compound. The produced 1-thio-alkyl-isoindole derivative exhibited very high emission activity in a faintly alkaline aqueous solution that could be monitored at 448 nm (excitation at 334 nm). 2-Amino-6-methyl-6-hydroxy-heptane was selected as the primary amine candidate that gave the high fluorescence intensity with the stability of the formed product. At the optimal experimental condition, the intensity of fluorescence of the formed product was linearly related to the concentration of captopril in 20-450 ng mL^-1 range. Commercial pharmaceutical tablets were analyzed, and the obtained results agreed with those of the published method regarding precision and accuracy. The mechanism of the reaction was discussed. In addition, the greenness of the approach was rated following eco-scale criteria.

Chemical stability and interactions in a new antihypertensive mixture containing indapamide and dihydralazine using FT-IR, HPLC and LC-MS methods

Indapamide and dihydralazine can be combined in fixed-dose formulations because of their complementary actions against hypertension. On the other hand, combined formulations present the problem of chemical interactions between the active ingredients, e.g. accelerated degradation of constituents or generation of quite new degradation products. Therefore, the main goal of the present study was to examine the chemical stability of indapamide and dihydralazine, as individuals and as a mixture, to detect potent interactions between both constituents, using FT-IR, HPLC and LC-MS methods. It was clearly shown that both drugs degraded more when they were in the mixture, i.e. indapamide was degraded more under high temperature/high humidity while dihydralazine was more sensitive to UV/VIS light. In solutions, indapamide was sensitive to strong acidic and strong alkaline conditions while dihydralazine degraded at pH ≥ 7. Generally, the process of degradation of indapamide and dihydralazine followed first order kinetics. The fastest degradation of both indapamide and dihydralazine was found at pH ≥ 10. Several degradation products of indapamide and dihydralazine were detected and identified by our LC-MS method. Interactions between both drugs were confirmed by detection of new degradation products of indapamide, i.e. 4-chloro-3-sulfamoylbenzamide and 4-chloro-3-(formylsulfamoyl)-N-(2-methyl-2,3-dihydro-1H-indol-1-yl)benzamide, only in the presence of dihydralazine.

New degradation pathway of indapamide in presence of dihydralazine.

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.