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J Dingemanse - One of the best experts on this subject based on the ideXlab platform.

Pekka T. Männistö - One of the best experts on this subject based on the ideXlab platform.

  • Optimization of the hydrolysis of conjugated L-DOPA, dopamine and Dihydroxyphenylacetic Acid in human urine for assay by high-performance liquid chromatography with electrochemical detection.
    Clinical Chemistry and Laboratory Medicine, 1997
    Co-Authors: Päivi Tuomainen, Pekka T. Männistö
    Abstract:

    Summary: Conjugates of the catechol compounds, L-dihydroxyphenylalanine (L-DOPA), dopamine and Dihydroxyphenylacetic Acid in human urine were analysed using the isocratic ion-pair reversed-phase HPLC method with electrochemical detection. Acid hydrolysis, using 4 mol/1 HC1 for 60 min, was more effective than treatment with sulphatase for the generation of free catechols. Free (non-conjugated) catechols already present, as well as those produced by either of the hydrolysis procedures, were adsorbed onto aluminium oxide and extracted in Acid solution. The repeatability of the technique for within and between-batch urine analysis was less than 2% and 8%, respectively. Free urinary dopamine (and Dihydroxyphenylacetic Acid) concentrations were much higher in the urine of patients treated with L-DOPA for Parkinson's disease than in healthy volunteers. At high dopamine (and Dihydroxyphenylacetic Acid) levels the conjugation capacity was apparently exceeded, since the overall percent conjugation of LDOPA, dopamine and Dihydroxyphenylacetic Acid was decreased "concentration dependency" when the concentrations of free catechols were increased. Both in the control group and L-DOPA-treated groups, enzymatic hydrolysis was much less effective than Acid hydrolysis in generating free catechols. This indicated that there were other, nonsulphated conjugates in the urine, accounting for between 66 and 100% of total conjugates.

  • optimization of the hydrolysis of conjugated l dopa dopamine and Dihydroxyphenylacetic Acid in human urine for assay by high performance liquid chromatography with electrochemical detection
    Clinical Chemistry and Laboratory Medicine, 1997
    Co-Authors: Päivi Tuomainen, Pekka T. Männistö
    Abstract:

    Conjugates of the catechol compounds, L-dihydroxyphenylalanine (L-DOPA), dopamine and Dihydroxyphenylacetic Acid in human urine were analysed using the isocratic ion-pair reversed-phase HPLC method with electrochemical detection. Acid hydrolysis, using 4 mol/l HCl for 60 min, was more effective than treatment with sulphatase for the generation of free catechols. Free (non-conjugated) catechols already present, as well as those produced by either of the hydrolysis procedures, were adsorbed onto aluminium oxide and extracted in Acid solution. The repeatability of the technique for within and between-batch urine analysis was less than 2% and 8%, respectively. Free urinary dopamine (and Dihydroxyphenylacetic Acid) concentrations were much higher in the urine of patients treated with L-DOPA for Parkinson's disease than in healthy volunteers. At high dopamine (and Dihydroxyphenylacetic Acid) levels the conjugation capacity was apparently exceeded, since the overall percent conjugation of L-DOPA, dopamine and Dihydroxyphenylacetic Acid was decreased "concentration dependently" where the concentrations of free catechols were increased. Both in the control group and L-DOPA-treated groups, enzymatic hydrolysis was much less effective than Acid hydrolysis in generating free catechols. This indicated that there were other, non-sulphated conjugates in the urine, accounting for between 66 and 100% of total conjugates.

George V. Rebec - One of the best experts on this subject based on the ideXlab platform.

  • Regional distribution of ascorbate and 3,4-Dihydroxyphenylacetic Acid (DOPAC) in rat striatum.
    Brain Research, 1991
    Co-Authors: Allison Basse-tomusk, George V. Rebec
    Abstract:

    In vivo voltammetry was used to study the regional distribution of extracellular ascorbate (AA) and 3,4-Dihydroxyphenylacetic Acid (DOPAC), a major dopamine metabolite, in the striatum of the rat. An electrochemically-modified carbon-fiber electrode, which provides distinct oxidation curves for each of these substances, was lowered in 1-mm increments through one of four striatal regions selected to sample the entire extent of this structure, including the nucleus accumbens. In anteromedial striatum, the level of AA was highest in the most dorsal and ventral aspects and lowest in the middle, whereas DOPAC levels generally showed the opposite pattern. This inverse relationship between AA and DOPAC was not evident in either lateral or posterior areas. To the extent that AA and DOPAC are released from different axon terminals, as mounting evidence suggests, regional differences in the extracellular concentration of these compounds may reflect the different and, in some cases, reciprocal distributions of two neuronal populations.

Velia La Pesa - One of the best experts on this subject based on the ideXlab platform.

  • A rapid and simple method for the determination of 3,4-Dihydroxyphenylacetic Acid, norepinephrine, dopamine, and serotonin in mouse brain homogenate by HPLC with fluorimetric detection.
    Journal of Pharmaceutical and Biomedical Analysis, 2014
    Co-Authors: Giuseppe E. De Benedetto, Daniela Fico, Antonio Pennetta, Cosimino Malitesta, Giuseppe Nicolardi, Dario Domenico Lofrumento, Francesco De Nuccio, Velia La Pesa
    Abstract:

    A fast and simple isocratic high-performance liquid chromatography method for the determination of 3,4-Dihydroxyphenylacetic Acid (DOPAC), norepinephrine (NE), dopamine (DA), and serotonin (5-HT) in homogenate samples of mouse striatum employing the direct fluorescence of the neurotransmitters is described. The method has been optimized and validated. The analytes were separated in 15min on a reversed-phase column (C18) with acetate buffer (pH 4.0, 12mM)-methanol (86:14, v/v) as mobile phase; the flow rate was 1ml/min. The fluorescence measurements were carried out at 320nm with excitation at 279nm. The calibration curve for DA was linear up to about 2.5μg/ml, with a coefficient of determination (r(2)) of 0.9995 with a lower limit of quantification of 0.031μg/ml. Since the procedure does not involve sample pre-purification or derivatisation, the recovery ranged from 97% to 102% and relative standard deviation (RSD) was better than 2.9%, the use of the internal standard is not mandatory, further simplifying the method. Similar performance was obtained for the other analytes. As a result, thanks to its simplicity, rapidity and adequate working range, the method can be used for the determination of 3,4-Dihydroxyphenylacetic Acid, dopamine, norepinephrine and serotonin in animal tissues. An experimental 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson-like disease has been used to demonstrate the method is fit-for-purpose.

Hong Zhao - One of the best experts on this subject based on the ideXlab platform.

  • simultaneous determination of 3 4 Dihydroxyphenylacetic Acid uric Acid and ascorbic Acid by poly l arginine multi walled carbon nanotubes composite film
    Journal of Nanoscience and Nanotechnology, 2011
    Co-Authors: Hong Zhao, Ying Xue, Zhuobin Yuan
    Abstract:

    The poly(L-Arginine)(PArg)-multiwalled carbon nanotubes (MWCNTs) composite film was used to modify glassy carbon electrode (GCE) to fabricate PArg/MWCNTs/GCE through electropolymerization of L-Arginine on MWCNTs/GCE. The PArg/MWCNTs/GCE exhibited high electro-catalytic activities towards the oxidation of 3,4-Dihydroxyphenylacetic Acid (DOPAC), uric Acid (UA), and ascorbic Acid (AA), and could be sensitively used for simultaneous determination of DOPAC, AA, and UA in pH 7.4 phosphate-buffered solution (PBS).The linear ranges were 7 microM to 2.7 mM for DOPAC, 3 microM to 1.2 mM for UA, and 70 microM to 1.4 mM for AA. The detection limits were 1.3 microM for DOPAC, 0.7 microM for UA and 20 microM for AA.

  • poly pyridine 3 boronic Acid multiwalled carbon nanotubes modified glassy carbon electrodes for simultaneous determination of ascorbic Acid 3 4 Dihydroxyphenylacetic Acid and uric Acid
    Electroanalysis, 2010
    Co-Authors: Hong Zhao, Ying Xue, Zhuobin Yuan
    Abstract:

    Poly(pyridine-3-boronic Acid) (PPBA)/multiwalled carbon nanotubes (MWCNTs) composite modified glassy carbon electrode (GCE) was used for the simultaneous determination of ascorbic Acid (AA), 3,4-Dihydroxyphenylacetic Acid (DOPAC) and uric Acid (UA). The anodic peaks for AA, DOPAC and UA at the PPBA/MWCNTs/GCE were well resolved in phosphate buffer solution (pH 7.4). The electrooxidation of AA, DOPAC and UA in the mixture solution was investigated. The peak currents increase with their concentrations increasing. The detection limits (S/N=3) of AA, DOPAC and UA are 5 µM, 3 µM and 0.6 µM, respectively.

  • Electrochemical sensing of melamine with 3,4-Dihydroxyphenylacetic Acid as recognition element
    Analytica Chimica Acta, 2010
    Co-Authors: Qian Cao, Hong Zhao, Nan Ding, Jian Wang
    Abstract:

    Abstract A new electrochemical sensor for melamine with 3,4-Dihydroxyphenylacetic Acid as the recognition element is established. The results of Fourier Transform Infrared (FT-IR) spectra demonstrate that melamine may interact with 3,4-Dihydroxyphenylacetic Acid to form a complex mainly through the hydrogen-bonding interaction. The electrochemical behavior of 3,4-Dihydroxyphenylacetic Acid in the presence of melamine was studied. The anodic peak currents of 3,4-Dihydroxyphenylacetic Acid obtained by differential pulse voltammetry are linear with the logarithm of melamine concentrations in the range from 1.0 × 10 −8 to 5.0 × 10 −6  M with a linear coefficiency of 0.997. The detection limit is 3.0 × 10 −9  M. The proposed method displayed an excellent sensitivity and was successfully applied to the determination of melamine in milk products.