A simple spectrophotometric method for the determination of methyldopa using p-chloranil in the presence of hydrogen peroxide

Abstract

A simple, rapid and sensitive spectrophotometric method has been developed for the determination of methyldopa in pharmaceutical formulations. The method is based on the reaction between tetrachloro-p-benzoquinone (p-chloranil) and methyldopa, accelerated by hydrogen peroxide (H 2 O 2 ), producing a violet-red compound (λmax = 535 nm) at ambient temperature (25.0 ± 0.2 0 C). Experimental design methodologies were used to optimize the measurement conditions. Beer's law is obeyed in a concentration range from 2.10 x 10 -4 to 2.48 x 10 -3 mol L -1 (r = 0.9997). The limit of detection was 7.55 x 10 -6 mol L -1 and the limit of quantification was 2.52 x 10 -5 mol L -1 . The intraday precision and interday precision were studied for 10 replicate analyses of 1.59 x 10 -3 mol L -1 methyldopa solution and the respective coefficients of variation were 0.7 and 1.1 %. The proposed method was successfully applied to the determination of methyldopa in commercial brands of pharmaceuticals. No interferences were observed from the common excipients in the formulations. The results obtained by the proposed method were favorably compared with those given by the Brazilian Pharmacopoeia procedure at 95 % confidence level.

Development of a Sequential Injection Analysis System for the Determination of Saccharin

“…The violet-red color development is based on the rapid formation of the complexes that is the result of the reaction of saccharin with p-chloranil (π acceptor) in the presence of H 2 O 2 [ 18 ]. Gotardo et al [ 19 ] also stated that the molecular interactions between the electron donors and the acceptors are generally associated with the formation of intensely colored charge-transfer complexes and radical ions, which absorb the radiation in the visible region of the spectrum (λ = 420 nm), as shown in Figure 2 . The spontaneous formation of the violet-red color from the yellow appearance of the p-chloranil upon the reaction with the saccharin is sufficient evidence of the formation of a charge-transfer complex.…”

Spectrophotometric determination of methyldopa by oxidative coupling reactions using 2,4 -dinitrophenylhydrazine reagent

“…At 428 nm, the absorbance of solutions and imitation solutions was compared. Since Table (5) indicates that 0.5 ml is the optimal volume for the reagent, this value was used in the following trials.…”

“…0.078 µg/ml, and the limit of quantification (LOQ) was 0.261 µg/ml. Figure (5) shows the standard curve for methyldopa…”

“…The drug's side effects include drowsiness, stomach pain, pancreatitis, slow muscle movement, jaundice, hepatitis, and swelling in the feet [1,2]. Various techniques have been described for estimating dopa, including spectroscopic methods [3][4][5][6][7][8][9][10][11][12][13][14], chromatography [15,16], and voltage measurement. These techniques are effective in estimating dopa in people with decreased kidney function, depression, and mental disorders [17].…”

Application of Cloud Point Method for Spectrophotometric Determination of Salbutamol Sulphate and Methyldopa

“…For the determination of salbutamol sulphate and methyldopa, different analytical techniques have been proposed, like spectrophotometric [4][5][6][7][8][9][10][11][12][13][14][15], chromatographic [16][17][18][19], voltammetric [20][21], potentiometric [22], flow injection [23] and kinetic [24] methods. Our determination of salbutamol sulphate and methyldopa spectrophotometrically is actually new, simple, and sensitive.…”