June 2013, Volume 4, No.3 International Journal of Chemical and Environmental Engineering Liquid Chromatographic Determination of Dopamine, Methyldopa, L-Dopa and Tyrosine in Pharmaceutical Preparations using 2- Hydroxynaphthaldehyde as a Derivatizing Reagent Asghar Ali Majidano*, Subhan Ali Majidano, Malik Alamgir, Muhmmad Yar Khuhawar Institute of Advanced Research Studies in Chemical Sciences, University of Sindh ,Jamshoro, Pakistan. *Corresponding Author:asgharalimajidano@yahoo.com Abstract: Analytical procedure has been developed for the determination of dopamine (DA) methyldopa (MD) levodopa (L-dopa) and Tyrosine (TY) by High Performance Liquid Chromatography using 2-hydroxynaphthaldehyde as a pre-column derivatizing reagent. The separation was achieved from Phenomenex C – 18, 5 μm (150×4.6 mm id) column, when eluted isocritically with methanol – acetonitrile-water (55; 4; 41 v/v/v) with a flow rate of 1ml/min. The detection by UV was at 280 nm. The linear calibration curves were obtained within the range of 3-10 μg/ml with a limit of detection within 0.072-0.088 μg/ml for each of the compound.The derivatization, separation and quantitation was repeatable with relative standard deviations (RSDs) within 2.5-4.4% (n=5). The method was applied for the determination of dopamine methyldopa, L-dopa and tyrosine from pharmaceutical preparations with RSDs within 2.4 - 4.5% (n=3) and results agreed with labeled values. The pharmaceutical preparations were also analyzed by standard addition and recovery of analytes was calculated within 95 – 98% with RSD 4.4 %. The pharmaceutical additives did not interfere the determination. Keywords: Dopamine, Methyldopa, Levodopa , Tyrosine, HN, Aldomet and Solger, Pre-column derivatization. 1. Introduction Dopamine (Dihydroxyphenylethylamine) (DA) is an important neurotransmitter in the mammalian central nervous system and is a member of catecholamines. DA is involved in neuropsychiatric disorders such as. Parkinsons' disease [1], Schizophorenia [2], epilepsy [3], attention deficit hyperactivity disorder [4] and drug dependence [5]. Levodopa (L-3, 4-dihydroxyphenylalanine) (L-dopa) is most commonly used symptomatic treatment for Parkinson's disease, but is itself largely inert. L-dopa is able to cross the blood brain barrier and is decarboxylated to DA by dopa decarboxylase [6,7]. In the human body L-dopa is synthesized from amino acid tyrosine (TY) by tyrosine hydroxylase [8]. Methyldopa (MD) is an important antihypertensive that take part in the catecholamine metabolic pathway and could therefore alter the entry and metabolism of L-dopa in the brain [9]. DA, MD, L-dopa and TY are important biological compounds and are present in pharmaceutical preparations. Their determination individually and in combination with the drugs in dosage form, could be of analytical interest in quality control. The reagent 2-hydroxynaphthaldehyde (HN) has related structure to naphthalenedialdehyde and has been used for HPLC determination of Putrescine and caduerine [34], glutamine [35], 2- aminobutyric acid [36]. The present work examines HN for the HPLC coupled with commonly available UV detection for the determination of DA, L-dopa, MD and TY from pharmaceutical preparations. The conditions are optimized for pre-column derivatization, HPLC separation, quantitative determination and validation of analytical procedures. 2. Experimental The standard solutions containing (1 mg/ml) of dopamine (DA), methyl-dopa (MD), levodopa (L-dopa) Tyrosine (TY) (E-Merck, Germany) were prepared in 0.1M hydrochloric acid by dissolving 50mg each in 50 ml acid solution. Further solutions were prepared by appropriate dilution as required. 2-hydroxynaphthaldehyde (HN) (Fluka, Switzerland), methanol (E-Merck, Germany), acetonitrile (J.T Baker, Holand),sodium hydroxide (Fluka, Switzerland), hydrochloric acid (37%), potassium chloride, acetic acid , sodium acetate, sodium bicarbonate,