A new spectrophotometric method for the determination of methyldopa

Abstract

A new, simple and low cost spectrophotometric method for the determination of methyldopa in pharmaceutical preparations was developed. The method was based on the coupling of methyldopa with 2,6-dichloroquinone-4-chlorimide (DCQ). The absorbance maximum (λ max) of the resulted colored product was at 400 nm. Different buffers were used to determine the optimal pH for the reaction. About 1% w/v acetate buffer with pH 8.0 gave the optimal pH required for the reaction. Of the different solvents tried, water and ethanol were found to be the most suitable solvents. Beer's law was obeyed in concentration range of 4-20 μg/ml methyldopa. The correlation coefficient was found to be (r = 0.9975). The limit of detection and limit of quantification were 1.1 μg/ml and 3.21 μg/ml, respectively. The reaction ratio between methyldopa and DCQ was studied and found to be 1:3. The work included the study of the possible interference of hydrochlorothiazide found in combination with methyldopa tablets. The method was validated and results obtained for the assay of two different brands of methyldopa tablets were compared with the BP method (colorimetric). The repeatability and reproducibility of the developed method were evaluated and the obtained results quoted. The derivative formed as a result of the reaction of methyldopa with DCQ was isolated and its possible mechanistic pathway was suggested.

Application of multivariate optimization to electrochemical determination of methyldopa drug in the presence of diclofenac at a nanostructured electrochemical sensor

“…Various analytical techniques have been reported for the determination of MD in pharmaceutical formulations and biological fluids such as high-performance liquid chromatography [10][11][12], potentiometry [13], spectrophotometry [14][15][16], NMR spectroscopy [17], and fluorometry [18]. Some of these methods are not simple and others are time consuming or involve procedures with rigorous control of the experimental conditions or require expensive equipment and consequently are not suitable for routine analysis.…”

A novel sensitive colorimetric determination of catecholamine drug in dosage form via oxidative coupling reaction with MBTH and potassium ferricyanide

“…Many spectrophotometric procedures have been proposed for the estimation of MD in pharmaceutical preparations including difference UV-spectrophotometric assay in the presence of germanium dioxide at 292 nm [22], Flowinjection spectrophotometry [23][24][25][26], fluorimetry [27,28], kinetic spectrophotometry [29][30][31] and extractive spectrophotometry [32,33]. Moreover, the colorimetric method was the most widespread for estimation of MD in dosage form using I2 solution with acetate buffer of pH 4.7 [4], 2-aminothiazole in alkaline medium [25], thiosemicarbazide in presence of ferric nitrate [26], NH4VO3 in the presence H3PO4 [34], (NH4)6Mo7O24.4H2O solution in H2SO4 [35], Fe(III)-ophenanthroline [36], barbituric acid [37], isoniazid in presence of Nbromosuccinamide [38], diazotised sulphanilamide in the presence of molybdate [39], periodate in H2SO4 and determination of unreacted periodate by adding methylene blue and KI [40], iron (III) in the presence of 1,10phenanthroline and 2,2'-bipyridyl [41], p-nitroaniline in the presence of molybdate ions in acidic medium [42], Ce(IV) nitrate solution in H2SO4 [43], bromothymol blue in alkaline medium [44], sodium nitrite in an acid medium and further reacting the resultant nitroso derivative with sodium hydroxide [45], 2,2-diphenyil-picrylhydrazyl [46], 2,6dichloroquinone-4-chlorimide in acetate buffer and in water and ethanol solvents [47] and p-phenylenediamine in phosphate buffer at pH 7.4 [48]. 3-methylbenzothiazolin-2one hydrazone hydrochloride (MBTH) was used with (NH4)2SO4.Ce(SO4)2 in acetone or with K2Cr2O7 in methanol medium to determine MD.…”

Nanomolar Determination of Methyldopa in the Presence of Large Amounts of Hydrochlorothiazide Using a Carbon Paste Electrode Modified with Graphene Oxide Nanosheets and 3‐(4′‐Amino‐3′‐hydroxy‐biphenyl‐4‐yl)‐acrylic Acid

“…It is a centrally acting α‐2‐adrenoceptor agonist, which reduces the sympathetic tone of muscles and produces a fall in blood pressure. This catecholamine contains a chiral centre and can therefore occur either as an S ‐ or R ‐isomer, and has antihypertensive activity due to the S ‐isomer 2. The therapeutic concentration of methyldopa in human plasma is usually in the range of 0.1–0.5 mg/L, and its average terminal elimination half‐life is 2 h 3, 4.…”