Objective: To develop and validate new, selective spectrophotometric colorimetric analytical methods for the quantification of methimazole in its pure form and in its pharmaceutical preparations.
Methods: Method A is based on the oxidation of methimazole with potassium permanganate in alkaline medium, the manganate ion produced was measured at λmax= 610 nm. Method B is a kinetic determination of methimazole using fixed-time method based on the oxidation of methimazole using known excess of cerium (IV) nitrate in acidic medium and assessing the unreacted Ce (IV) by adding a fixed amount of methyl orange and measuring the absorbance of the resultant solution at λmax=507 nm which is equivalent to the unreacted methyl orange. The reaction conditions and analytical parameters are investigated and optimized. Method validation was carried out according to ICH guidelines in terms of linearity, LOD, LOQ, precision, and accuracy.
Results: Beer’s law is obeyed in the range of 1.50–15.00 μg/ml for method A and 0.25–3.00 μg/ml for method B. The developed methods were subjected to the detailed validation procedure. The proposed spectrophotometric methods were applied for the determination of the methimazole in its pure form and in its pharmaceutical formulation. The percentage recoveries were found to be 100.82 % and 99.85 % in the pharmaceutical formulation for the two proposed methods, respectively.
Conclusion: Both developed spectrophotometric methods, considered as green analytical chemistry, were found to be novel, highly selective and can be applied for the quality control of methimazole in its pure form and in its pharmaceutical formulation based on the simplicity, applicability of the parameters, accessibility of the reagents employed and reasonably low time of analysis.
Objective: A comparative study of smart spectrophotometric chemometric assisted techniques and RP-HPLC for the determination of candesartan cilexetil (CAN)-pitavastatin calcium (PIT) and clopidogrel bisulfate (CLO)-rosuvastatin calcium (ROS), binary co-administered drugs were developed and validated.
Methods:The spectrophotometric chemometric assisted methods included two simple techniques, namely Fourier transform convolution (FF) and ratio spectra of Fourier transform convolution (FFR) methods. FFR is considered as a hybrid divisor ratio spectra method where Fourier functions are applied to divisor ratio signals. The RP-HPLC method involves a rapid separation on a C18 column using a mobile phase consisting of acetonitrile: sodium dihydrogen phosphate (adjusted to pH 2.6 using orthophosphoric acid) in the ratio of 70:30 v/v at a flow rate of 1 ml/min in isocratic mode. CLO and ROS were monitored at 220 nm however CAN and PIT were monitored at 238 nm.
Results:The spectrophotometric chemometric assisted methods proved their ability to quantify each of the studied drugs in their binary mixtures, where excellent percentage recoveries were obtained. FF and FFR method proved to be linear over the concentration range of 10-50 µg/ml for CLO, 4-20 µg/ml for ROS, 8-20 µg/ml for CAN and 2-10 µg/ml for PIT. The RP-HPLC method was able to separate the drugs in the study; retention times were found to be 3.9 min and 14.4 min for ROS-CLO, 4.2 min and 14.5 min for PIT-CAN respectively. The RP-HPLC method was found to be linear in the concentration range of 0.1-0.5 µg/ml for CLO, 0.04-0.2 µg/ml for ROS, 0.5-1 µg/ml for CAN and 0.05-0.1 µg/ml for PIT. System suitability parameters proved that peaks were well resolved from each other.
Conclusion:The spectrophotometric and chromatographic methods were validated according to ICH guidelines. Recovery was found to be in the range of 95.9 %-100.5 % in synthetic laboratory mixtures. The suggested spectrophotometric methods have the advantage over other methods that they do not require a preliminary separation. Statistical analysis between the suggested spectrophotometric chemometric assisted and RP-HPLC methods, using student's t-and F-test revealed that there is no difference between the applied methods.
A simple, automated and sensitive reversed flow-injection analysis (rFIA) method for the determination of chlorpromazine hydrochloride (CLP) in pharmaceutical formulations and human urine samples is described. The automated method is based on the formation of charge-transfer complex between CLP (donor) with new reagent (an acceptor) used for the first time namely, 4,4'-tetramethyl-diaminodiphenylmethane (TDM) in the presence of K2S2O8 as an oxidant. An intense blue-colored product, which gave a maximum absorbance at 604 nm, was formed immediately at room temperature. The various chemical and physical conditions that affected the reaction have been studied. The calibration curve was rectilinear within the concentration range 1-45 µg/mL and the detection and quantification limits of 0.72 and 2.40 µg/mL respectively with a sample through put of 80 sample/hour. The proposed procedure was applied successfully for the estimation of CLP and the results obtained were favorably compared with those given by a reference method, and there was no significant difference between the obtained results, regarding accuracy and precision at the 95% confidence level.
A new reverse flow injection system combined with a solid-phase reactor containing PbO2 was suggested for spectrophotometric determination of nitrazepam in pharmaceutical tablets. Nitrazepam was measured by coupling with a new reagent (2,2'-dihydroxybiphenyl) oxidized by forced through the reactor containing PbO2 immobilized in a polymeric matrix. The absorbance of the resultant blue colored product was measured at 635 nm, and the calibration graph for nitrazepam was linear in the 10 to 300 µg/mL concentration range with RSD of less than 2.5% (n = 38) and a sample throughput of 40 h-1. The influence of the variables of flow system and solid-phase reactor such as composition, size of particles and length of the reactor, were studied. The proposed method was applied for determining nitrazepam in two commercial tablets without any interferences.
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