Determination Of Dopa Research Articles

Flow-Injection Amperometric Determination of DOPA and Tyrosine at a Dual Electrode Modified with the Gold–Cobalt Binary System

The gold–cobalt binary system, electrodeposited on the surface of a screen-printed electrode, exhibits catalytic activity in the electrooxidation of DOPA and tyrosine. The catalytic effect is shown in a multiple increase in current compared with the oxidation current of the modifier and a decrease in the oxidation overvoltage of organic compounds. Methods for the flow-injection amperometric determination of DOPA and tyrosine at the proposed modified electrode are developed. The simultaneous amperometric determination of DOPA and tyrosine at a dual screen-printed electrode modified with an Au–Co binary system the under conditions of flow-injection analysis is demonstrated. The linear dependence of the analytical signal on the concentration of DOPA and tyrosine is observed in the ranges from 1 × 10–9 to 1 × 10–4 M and from 5 × 10–8 to 5 × 10–4 M, respectively.

Enantiomeric Determination of DOPA in Dietary Supplements Containing <i>Mucuna pruriens</i> by Liquid Chromatography/Mass Spectrometry

We developed a simple and rapid liquid chromatography/mass spectrometry (LC/MS) method for the enantiomeric determination of DOPA in dietary supplements containing Mucuna pruriens. L- and D-DOPA were ultrasonically extracted with 1% formic acid aqueous solution. The isolated extracts were analyzed by LC/MS using a Crownpak CR (-) column at 30℃. The mass spectrometer was operated in the positive mode of electrospray ionization, and the mobile phase was aqueous formic acid (pH 2.0). L-DOPA-ring-d3 was used as an internal standard. The method was validated for a dietary supplement spiked with L- and D-DOPA at 50 and 500 μg/g, respectively, and the recoveries of the DOPA enantiomers were between 97.5% and 101.3%. Relative standard deviation values of repeatability and intermediate precision were less than 7%. The method was applied to 14 dietary supplements. L-DOPA was detected in these supplements in the range of 0.88-12.8 mg/unit. D-DOPA was not detected.

Characterization of MWCNTs-PMel Composite Film and Its Application in Simultaneous Determination of DOPA and Serotonin

A composite film, which contains multiwalled carbon nanotubes (MWCNTs) incorporated with poly(melatonin) (PMel), has been synthesized on gold electrode by the potentiodynamic method. The presence of MWCNTs in the MWCNTs-PMel composite film enhances surface coverage concentration of PMel to ≈640% and increases the electron-transfer rate constant to ≈17%. The surface morphology of the MWCNTs-PMel composite film deposited on gold electrode has been studied using scanning electron microscopy and atomic force microscopy. These two techniques reveal that PMel is incorporated in MWCNTs. Electrochemical quartz crystal microbalance study reveals the enhancement in the functional properties of MWCNTs and PMel. The MWCNTs-PMel composite film exhibits enhanced electrocatalytic activity toward the biochemical compound mixture containing 3,4-dihydroxy-L-phenylalanine (DOPA) and serotonin. The electrocatalytic responses of these analytes at PMel, MWCNTs, and MWCNTs-PMel films were measured using cyclic voltammetry. From the electrocatalysis studies, well-separated voltammetric peaks have been obtained for DOPA and serotonin in MWCNTs-PMel composite film, with a peak separation of 145.1 mV. The sensitivity of MWCNTs-PMel composite film toward DOPA and serotonin is 0.4 and , respectively. Similarly, the sensitivity of MWCNTs-PMel composite film toward DOPA and serotonin present in the mixture is 0.46 and , respectively. These sensitivity values of MWCNTs-PMel composite film are higher than the PMel and MWCNT films.

Chiral and non chiral determination of Dopa by capillary electrophoresis

The suitability of capillary electrophoresis for determining the enantiomeric purity of levodopa in a pharmaceutical formulation also containing benserazide was assessed. To this end, the pharmaceutical components were separated in a non-chiral medium that allowed the total amount of Dopa and that of benserazide to be quantified. The addition of a chiral crown ether to the background electrolyte allows to separate the enantiomers of this compounds. Optimizing the variables influencing the enantioresolution of Dopa affords a resolution high enough resolution to determine the amount of dextrodopa (the distomer) contained in levodopa (the eutomer) in a pharmaceutical. A relative limit of detection (RLD) is proposed as a measure of the lowest detectable enantiomeric impurity. The RLD for the determination of dextrodopa contained in levodopa was 0.1% and found to depend on the enantiomer migration order. The enantiomeric purity of levodopa in the pharmaceutical preparation and dextrodopa from Sigma was 99.5 and 99.95%, respectively.

Determination of DOPA by Spectrophotometric Method

Determination of DOPA by Spectrophotometric Method

A nonisotopic method for determination of the in vivo activities of tyrosine hydroxylase in the rat adrenal gland

A rapid and reliable method for determination of in vivo activities of tyrosine hydroxylase in the rat adrenal gland is presented. This method involves determining the rate of accumulation of 3,4-dihydroxyphenylalanine (Dopa) in the adrenal gland after decarboxylase inhibition by NSD 1015, using HPLC with electrochemical detection after purification of the acid-deproteinized tissue extract with Bio-Rex 70 columns followed by alumina batch method. Purification of the sample with alumina adsorption alone, a method usually used for purification of catecholamines and Dopa, was ineffective: epinephrine and norepinephrine, which are present in high concentrations, interfered with an accurate determination of Dopa, and dopamine, which is retained strongly on the reverse-phase column, interfered with a rapid analysis. Purification with Sephadex G-10 columns followed by alumina adsorption was also ineffective. After purification with columns of weak cation-exchange resins such as Bio-Rex 70 or Amberlite CG-50 followed by alumina adsorption, most of the epinephrine and norepinephrine was removed and dopamine was eliminated. Thus a rapid and accurate determination of Dopa could be made. Of the two cation exchangers, Bio-Rex 70 was more effective. Accumulation of Dopa in the adrenal gland was linear up to 30 min after administration of NSD 1015 and a plateau was reached with doses over 10 mg/kg. Using this method, we investigated the effects of immobilization stress, reserpine, and hypoxia on in vivo activities of tyrosine hydroxylase in the adrenal gland.

Indirect potentiometric determination of α-amino acids with a copper-selective electrode and determination of dopa and methyldopa in pharmaceutical preparations

α-Amino acids which form soluble copper complexes can be determined by stoichiometric reaction with an excess of copper(II) phosphate suspension and measurement of the copper ions produced with a copper(II) ion-selective electrode. Amino acids in the range 5 X 10 −4−1 X 10 −2 M, separately or as a total value, can be determined with an accuracy better than 3%. l-Dihydroxyphenylalanine (dopa) and methyl derivative were determined in pharmaceutical preparations without interference from excipients; agreement with the results of USP methods was good.

Determination of DOPA, dopamine, and 5-S-cysteinyl-DOPA in plasma, urine, and tissue samples by high-performance liquid chromatography with electrochemical detection

Determination of DOPA, dopamine, and 5-S-cysteinyl-DOPA in plasma, urine, and tissue samples by high-performance liquid chromatography with electrochemical detection

A semiautomated method for the rapid determination of dopa: Comparison of plasma and erythrocyte-dopa concentration in levodopa-treated patients

A rapid, sensitive, and reproducible method for the semiautomated determination of plasma dopa has been developed. Dopa in deproteinized plasma or tissue is isolated by cation—exchange column chromatography, and is then processed through a Technicon AutoAnalyzer and quantitated as its hydroxyindole derivative by fluorescence spectrometry. Plasma-dopa concentrations as low as 0.3 μ m can be readily determined. Plasma and erythrocyte levels in parkinsonian patients are routinely assayed by this method in our laboratory. A correlation coefficient of 0.995 was given by a comparison between this automated method and the manual method. Plasma and erythrocyte levels of dopa and 3- O-methyldopa (OMD) were measured in 14 randomly selected patients, and correlations were made between these concentrations and the dosage of levodopa.

A simple radioenzymatic method to measure picogram amounts of DOPA in brain and biological fluids.

A simple radioenzymatic method for the determination of DOPA is described. The method is based on the conversion of DOPA to 3-O-[methyl-3H]DOPA by catechol-O-methyltransferase in the presence of S-adenosyl-[methyl-3H]methionine and purification of the labelled product by Sephadex G10 and Dowex 50 W x 4 ion exchange resin. The method has been applied to the assay of endogenous DOPA in different brain area and to measuring DOPA accumulation after inhibition of aromatic amino acid DOPA decarboxylase.

Determination of dopa, dopamine, dopac, epinephrine, norepinephrine, alpha-monofluoromethyldopa and alpha-difluoromethyldopa in various tissues of mice and rats using reversed-phase ion-pair liquid chromatography with electrochemical detection.

A method for the determination of catecholic amino acids and amines by reversed-phase ion-pair high-performance liquid chromatography with electrochemical detection has been developed. B using octanesulfonic acid for ion pairing and by optimising ionic strength, pH and methanol concentration of the mobile phase, separation was achieved of 3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), norepinephrine (NE), epinephrine (EPI), and dopamine (DA). Alpha-Difluoromethyldopa (DFMD) and alpha-monofluoromethyldopa (MFMD), two potent enzyme-activated irreversible inhibitors of aromatic amino acid decarboxylase were also separated from the natural catechols. Concentrations of catechols and inhibitors were measured in brains, hearts and kidneys of mice treated with small repeated doses of MFMD. The method has also been applied to the determination of catechols in other organs such as prostates and seminal vesicles of rats and in smaller tissues like mesenteric arteries. A semi-automated procedure making use of an automatic sample processor and a digital integrator permitted the analysis of as many as sixty samples per day.

5-S-cysteinyldopa in the urine of melanoma patients

A newly discovered amino acid, 5-S-cysteinyldopa, present in the urine of healthy subjects is excreted in pathological amounts in many patients suffering from melanoma metastases. Increased excretion of 5-S-cysteinyldopa may be observed before metastases become clinically evident. Determination of 5-S-cysteinyldopa is superior to determination of dopa+dopamine in the diagnosis of melanoma metastases.

Determination of Dopa in Pharmaceutical Dosage Forms Based on Oxidation at Tubular Carbon Electrode

Abstract: A method for the determination of dopa [3-(3,4-di-hydroxyphenyl)alanine] in pharmaceutical dosage forms based on electrochemical oxidation at the tubular carbon electrode is presented. A comparison with a colorimetric method shows this new method to be considerably faster and simpler without a significant loss in precision or accuracy. Between 25 and 30 samples may be determined each hour, for which the variance due to the method results in a standard deviation no greater than ± 0.9%.

A reliable and simple method for simultaneous determination of dopa and 3-O-methyldopa in plasma and brain

A rapid, simple, and reliable method for the simultaneous estimation of D and O-MD in plasma and brain is described. These compounds are eluted together, but separately from the catecholamines, by passing perchloric acid extracts through columns of a strong cation-exchange resin in the H + form. The pH of the eluate is adjusted with the addition of a Na 3 citrate solution. Specific oxidation of D and O-MD are carried out by reacting with iodine and ferricyanide, respectively. No interference with plasma D and O-MD measurements was found from the presence in plasma of drugs commonly used in the treatment of parkinsonism. The presence of hydrazinomethyldopa and α-methyldopa partially interferes with the determinations of D and O-MD. Plasma levels of O-MD are greater than D in patients receiving chronic l-dopa therapy.

A method for the determination of dopa and 3-O-methyldopa in the plasma of Parkinsonian patients.

A method is described for the determination of dopa and its metabolite 3-O-methyldopa in plasma. After precipitation of protein and elution from Dowex 50, dopa is determined using oxidation by ferricyanide. A second sample of the eluate is heated at pH 8.5 to destroy dopa and 3-O-methyldopa determined using oxidation by iodine. Applications of the method to plasma of Parkinsonian patients under treatment with L-dopa are described.

Excretion of L-Dopa and Its Metabolites in Urine of Parkinson's Disease Patients Receiving L-Dopa Therapy

Abstract L-Dopa and its major metabolites were separated from daily 24-h urines from patients with Parkinson’s disease, who were being treated with increasing doses of the drug, up to 4 g per day. An aliquot of each sample was passed through three different ion-exchange columns. Catecholamines (dopamine, epinephrine, norepinephrine, metanephrine, and normetanephrine) were retained on a cation-exchange column, eluted with boric acid, and quantitated by fluorometric analysis. Catechol acids, present in the effluent of the cation-exchange column, were retained on an anion-exchange column. An aliquot of the eluate of the anion-exchange column was used for colorimetric determination of 3,4-dihydroxyphenylacetic acid, while the effluent from this column was used for colorimetric determination of dopa. A second aliquot of the eluate from this column was passed over a column of alumina, which retained all the acidic metabolites except homovanillic acid, which was measured fluorometrically in the effluent from the alumina column. Vanilmandelic acid was determined in another aliquot of each urine sample by use of paper electrophoresis. The excretion pattern elicited suggests a major metabolic pathway for the L-dopa administered to patients with Parkinson's disease.

Dopa and 3- O-methyldopa in cerebrospinal fluid of parkinsonism patients during treatment with oral l-dopa

In a study of dopa metabolism as reflected in the cerebrospinal fluid of parkinsonism patients during l-dopa therapy, it became evident that 3- O-methyldopa is present in these fluids in a concentration eight to ten times that of dopa. This concentration is sufficiently high to cause significant interference in the determination of dopa if appropriate corrections are not made. New fluorimetric methods for the determination of 3- O-methyldopa and dopa in cerebrospinal fluid were devised. The procedure for determination of dopa has the advantage of greater sensitivity than the traditional iodine oxidation method. A thin-layer chromatographic search was made for the metabolites of 3- O-methyldopa, vanilpyruvic acid and vanillactic acid, in cerebrospinal fluid. Neither was found, suggesting that the 3- O-methyldopa in cerebrospinal fluid originates largely from systemic metabolism of dopa rather than from the central nervous system. These findings are discussed in the light of present trends in l-dopa therapy.

Biochemistry of Functional Neural Crest Tumors

Publisher Summary Catecholamine neurons are the cells that are capable of synthesizing, storing, and secreting catecholamines. In the sympathetic nervous system, there are two kinds of these cells—namely, the sympathetic ganglion cells and the chromaffin cells. In specific, functional neural crest tumors refer to catecholamines-producing tumors. This chapter describes the biochemistry of the functional neural tumors of the sympathetic nervous system and presents the metabolism of dopa, which is considered the main biochemical feature of these tumors. The metabolism of methionine and, especially of cystathionine and homoserine is also presented. The chapter also describes the different types of functional neural crest tumor. The methods for determination of dopa and its metabolites are of great importance for characterizing and diagnosing these tumors properly. The methods involve determination of amino acids, phenolic amines, phenolic alcohols, and phenolic acids in tumor, blood, and urine.

Metabolism of aromatic amino acids in collagen diseases. urinary excretion of vanillactic acid and dihydroxyphenylalanine

1. (1) Vanillactic acid was newly synthesized, and its chromatographic properties and reactions were investigated and found to be in satisfactory agreement with those of the naturally occurring vanillactic in the urine in rheumatic fever. 2. (2) Increased urinary excretion of DOPA was observed in children suffering from collagen diseases. A relatively simple procedure was devised for the semiquantitative determination of DOPA in the urine. 3. (3) Increased urinary output of an indole compound, probably 3-methoxy-tryptophan, was observed in rheumatic fever. 4. (4) Aspects of the metabolism of aromatic amino acids in rheumatic fever are discussed in relation to these findings.

Quantitative Determination of Dopa; Its Application to Measurement of Dopa in Urine and in the Assay of Tyrosinase in Serum

A persistent problem in the clinical management of primary melanoma is the detection of cryptic foci of metastatic melanoma. A specific chemical assay for tyrosinase or for one or more of the intermediates in the tyrosine-to-melanin metabolic pathway would be of value in estimating the degree of dissemination of the tumor. Such a test would prevent mutilating surgery or the use of a powerful and potentially injurious chemotherapeutic agent.