Two Spectrophotometric Assays for Dopamine Derivatives in Pharmaceutical Products and in Biological Samples of Schizophrenic Patients Using Copper Tetramine Complex and Triiodide Reagent
F. A. Nour El-Dien,1,3 M. A. Zayed,2 Gehad G. Mohamed,1 and Reham G. El-Nahas3∗1 Chemistry 2 Chemistry
Department, Faculty of Science, Cairo University, Giza 12613, Egypt Department, Faculty of Education of Girls, El-Qassem Borida, Saudi Arabia 3 Microanalytical Center, Faculty of Science, Cairo University, Giza 12613, Egypt Received 30 March 2004; revised 2 August 2004; accepted 24 August 2004
Two simple, rapid, and sensitive spectrophotometric methods are proposedfor the determination of levodopa (LD). The ﬁrst method is based on coupling of 4-aminoantipyrine (4-AAP) with one of the dopamine derivatives (LD, CD) to give a new ligand that reacts with copper tetramine complex to give intensely colored chelates. The colored products are quantiﬁed spectrophotometrically at 525 and 520 nm for LD and CD, respectively. The optimization of the experimentalconditions is described. The method has been used for the determination of 19.7–69.0 and 18.1–54.3 µg mL−1 of LD and CD, respectively. The accuracy of the method is achieved by the values of recovery (100 ± 0.2%) and the precision is supported by the low standard deviation (SD = 0.17–0.59) and relative standard deviation (CV = 0.4%–1.54%) values. The second method is based on the formation of ion-pairiodinated inner sphere or outer sphere colored complexes between the LD and triiodide ions at pH 5 and room temperature (23 ± 3◦ C). This method has been used for the determination of LD within the concentration range 39.44–78.88 µg mL−1 with SD = 0.22–0.24 and recovery percent = 100 ± 0.3%. The sensitivity of the two methods is indicated by Sandell’s sensitivity of 0.014–0.019 g cm−2 . The resultsof the two methods are compared with those of the oﬃcial method. The interference of common drug additives, degradation products, and excipients was also studied. The proposed methods were applied successfully to the determination of the LD-CD synthetic mixture and Levocare drug. The determination of LD in urine of some schizophrenic patients was applied with good precision and accuracy. Thereliability of the methods was established by parallel determinations against the oﬃcial British pharmacopoeia method.
INTRODUCTION The dopamine derivatives participate in the regulation of a wide variety of physiological functions in the human body and in medication life depending on their structures (Figure 1). Hormones act as chemical messengers controlling the activity of living things. They arereleased in small amounts in the blood stream from a number of vital sites especially some brain regions. Dopamine was recognized as a neurotrasmitter in its own right but the demonstration of its nonuniform distribution in the brain suggested that it might have a speciﬁc functional role of dopamine . It had an important role in the pathogenesis of drug treatment of certain brain diseases,Parkinson’s disease, and schizophrenia. Parkinson’s disease was associated with decrease of dopamine concentration in the brain (Nozaki Y, Abe T, Takahashi S,
1995), . So it must be medicated with drugs containing LD combined with a certain amount of CD, which makes LD available for transport to the brain and converted to dopamine in the basal ganglia [3, 4]. The brain of a schizophrenicpatients produces more dopamine, especially in the striatum of the brain, than the normal brain (see http://serendip.brynmawr.edu/bb/neuro/ neuro98/202s98-paper1/Frederickson.html). In this case, the drug used blocks dopamine receptors in the brain. The increasing awareness of the biological signiﬁcance of dopamine derivatives has promoted a great deal of research into their detection and quantitative...