PubMed · 3627466
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C G Goetz, C M Tanner, V S Carroll, K M Shannon, H L Klawans. 1987. Controlled-release Sinemet.. https://doi.org/10.1212/wnl.37.9.1567
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The enantiomeric separations of 3,4-dihydroxyphenylalanine (dopa) and 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid (carbidopa) by capillary electrophoresis were studied using several native, neutral and anionic cyclodextrins as chiral additives and uncoated fused-silica capillaries. The effect of the type and concentration of the cyclodextrin added to 20 mM phosphate buffer (pH 2.5) on enantioseparation and migration times was studied. A high resolution value of 15.63 was obtained for dopa enantiomers with a buffer containing 20 mM single isomer, heptakis(2,3-diacetyl-6-sulfato)-beta-cyclodextrin. The enantiomers of carbidopa were separated using 20 mM carboxymethyl-beta-cyclodextrin as a chiral resolving agent. Both methods allowed the determination of 0.1% of the D-enantiomer (second migrating) in the presence of the L-enantiomer (first migrating) of dopa and carbidopa with a good precision. These methods also gave good results in terms of precision for both peak area, migration time, linearity and accuracy.
Capillary electrophoresis (CE) was successfully applied to the enantiomer resolution of racemic structurally related compounds, namely dihydroxyphenylalanine (DOPA), methyldihydroxyphenylalanine (MDOPA) and hydrazinomethyldihydroxyphenylalanine (CDOPA). The chiral resolution was performed in an untreated fused-silica capillary by using a phosphate buffer at pH 2.5 or 3.0 supplemented with sulfobutylated beta-cyclodextrin (SBE-CD). Resolution was strongly influenced by the concentration of the chiral selector added to the background electrolyte. In fact, 2-5 mM of SBE-CD enabled the resolution of DOPA and MDOPA enantiomers, while CDOPA optical isomers were resolved by using either 0.5 mM or 6-20 mM of SBE-CD. The latter separation conditions (reversed polarity mode) made it possible to obtain inversion of migration order.
In this study levodopa (L-DOPA), carbidopa (C-DOPA) and their metabolites were resolved from other endogenous components present in human plasma and urine and determined quantitatively. The developed technique involved the use of a second pump, a switching valve, and a pre-column in the LC system in order to perform on-line sample clean-up and enrichment. This procedure is dependent on an effective removal of the many interfering matrix components that vitiate HPLC analysis. Several unknown endogenous electroactive compounds, present in plasma, were eliminated by the purification step, or suppressed by the pre-treatment or detection conditions. The analyses were separated on an Octyl-bonded reversed-phase column followed by amperometric detection using a carbon fibre microelectrode flow cell operated at +0.8 V versus silver/silver phosphate reference electrode. The cell was compatible with the mobile and the stationary phase used in the flow system without any complex surface reaction. The peak currents obtained for the different analytes were directly proportional to the analyse over the concentration range 0.02-4.0 microg ml(-1). Using this method, the minimum detectable concentration was estimated to be 5 and 8 ng ml(-1) for L-DOPA and C-DOPA, respectively. Recovery studies performed on human plasma samples ranged from 93.83 to 89.76%, with a relative standard deviation of < 6%. The intra- and inter-assay coefficients of variation were < 7%. The accuracy of the assay, which was defined as the percentage difference between the mean concentration found and the theoretical (true) concentration, was 12% or better. The electrochemical pre-treatment regime described in this work permitted a longer application of the same microelectrode. The method showed a good agreement with other available methods described in the introduction and offers the advantages of being simple, less time and labour consuming, does not require additional solvents for extraction, inexpensive and suitable for routine analysis and kinetic purposes.