Determination Of Neurotransmitters Based On The Capillary Electrophoresis Electrochemical Detection With Online Enrichment

CE has become a very popularity separation technique owing to its advantages of efficient, fast and small amount of samples and reagents required. However, CE analysis was still being limited in many areas become of the low sensitivity caused by disadvantages of the limited optical path and capillary length. Therefore, this article was carried out to focus on the online enrichment method research in CE to detect neurotransmitters, the main contents were as follows:In the chapter I, at first, the development, basic principle, detection method and application of capillary electrophoresis were briefly introduced, then the nature and detection method of dopamine and levodopa were simply described, and the present situation of the development, methods and application of electrochemical modified electrode were reviewed in detail. Finally, the online enrichment of capillary electrophoresis technology and application were mainly introduced.In the chapter II, first of all, in the conventional mode of capillary electrophoresis electrochemical detection, the best conditions to detect dopamine were optimized, the optimum conditions were 10 mmol·L-1 phosphate buffer(pH 7.5), 15 kV for the separation voltage, 1.2 V for the detection potential and 10 s for the injection time.Under this normal mode, the detection limit of dopamine was 8.8 x 10-7 mol·L-1. Then the dopamine was detected under the field amplified sample mode, the best conditions were the sample dissolved in pure deionized water solvent, the background buffer was60 mmol·L-1 phosphate buffer(pH 7.5), before electrokinetic injection sample introduced water for the best time was 6 s, the best sample time was 16 s. Under this enrichment mode, the detection limit of dopamine was 8.9 x 10-10 mol·L-1. Compared with the conventional capillary electrophoresis, the enrichment ratio was 989.In the chapter III, a new carbon fiber micro-disk bundle electrode was made, and it was modified with the melanin type polymer. Then the modified electrode was used to detect the dopamine. It has been discovered that the addition of ascorbic acid could significantly increase the oxidation signal of dopamine, through experiments we obtained that the content of ascorbic acid in the best was 1.0 x 10-3 mol·L-1. The best conditions to oxidate levodopa by potentiostatic method were: 50 mmol·L-1(pH7.4)phosphate buffer solution containing 3.0 x 10-3 mol·L-1 levodopa, the constant voltage was 1.2 V, the electrochemical polymerization time was 1.5 hours. Then the modified carbon fiber micro-disk bundle electrode was used as the working electrode,combined with field amplified sample method to detect dopamine, the phosphate buffer containing 1.0×10-3 mol·L-1 ascorbic acid, under the best conditions of the field amplified enrichment mode optimized in chapter II, the detection limit of dopamine was 4.9 x 10-10 mol·L-1. Compared with the conventional capillary electrophoresis, the enrichment ratio was 1796.In the chapter IV, firstly, the dopamine and levodopa were separated and tested with conventional capillary electrophoresis electrochemical detection, the best conditions were 50 mmol·L-1 borax buffer solution(pH 8.5), 12 kV for the separation voltage, 1.2 V for the detection potential and 8 s for the injection time. The detection limits were 5.1 x 10-7 mol·L-1 for dopamine and 4.7 x 10-7 mol·L-1 for levodopa. Then used the extremely large volume electrokinetic stacking method to enrich and separate the two substances, the best conditions for enrichment were the background buffer was25 mmol·L-1 borax buffer solution containing 40 mmol·L-1 SDS(pH 9.5), the sample preparated in the 20 mmol·L-1 sodium dihydrogen phosphate solution(pH 3.0), 12 kV and 25 minutes for the injection voltage and the injection time. The limits were 3.4 x10-10 mol·L-1 for dopamine and 2.8 x 10-10 mol·L-1 for levodopa. Compared with the conventional capillary electrophoresis, the enrichment ratio was 1500 and 1679 fordopamine and levodopa respectively, and shorten by 15 minutes for testing and separating the two substances.