| Ascorbic acid?AA?is a soluble vitamin widely present in food,animal body fluids,and organization and drug,and it has been used for prevention and treatment of mental illness,infertility and AIDS due to its anti-oxidation.Dopamine?DA?is one of the important catecholamine neurotransmitters in the mammalian central nervous system,and it is widely applied to the treatment of circulatory collapse syndrome caused by the myocardial infarction,trauma,endotoxin sepsis,cardiac surgery or congestive cardiac failure.Uric acid?UA?,a primary end product of purine metabolism,its abnormal level is commonly a symptom of some disease,like hyperpiesia,leukemia and pneumonia.Tyrosine?Tyr?is one of important components of protein,possessing an essential function of maintaining a balanced nutrition of human body,and the unbalanced of tyrosine will cause some disease as albinism,alkaptonuria,depressive disorder and other psychological illness.Xanthine?XN?and hypoxanthine?HXN?are the purine nucleotide catabolism of intermediates.Due to their abnormal levels,it can cause several diseases,such as gout,xanthine urine and hyperuricemia.However,the selective or simultaneous determinations of AA,DA,UA,Tyr,XN and HXN at bare electrodes are nearly impossible because the oxidation potential of AA,DA and UA are very close,and also,the oxidation products adsorbed on electrode surfaces can lead to poor sensitivity and selectivity.To overcome these problems,various modified electrodes have been constructed and used to selectively or simultaneously determine AA,DA,UA,Tyr,XN and HXN.Conjugated polymers always have irreplaceable position in the electrochemical academic due to their numerous advantages,such as strong selective,good stability,high repeatability,and the thickness of the electrode surface can be controlled.This paper includes three aspects as followed:1.A poly?1H-imidazole-4-carboxylic acid??PHIMC?film modified glassy carbon electrode?GCE??PHIMC/GCE?was fabricated by using simple cyclic voltammetry?CV?.The results show that the polymerized HIMC modified GCE?PHIMC/GCE?not only exhibits strong electro-catalytic activities toward oxidations of DA,UA and Tyr,but also can resolve the sluggish and overlapped voltammetric responses of DA,UA and Tyr into three strong and well-defined oxidation peaks by using both CV and DPV,which can be applied for the selective and simultaneous determinations of DA,UA and Tyr in a mixture.Under the optimum conditions,the linear dependences of DPV current responses are observed for DA,UA and Tyr in the concentration ranges of 0.5-40?mol L-1,2-310?mol L-1 and 8-420?mol L-1 with the correlation coefficients of 0.9989,0.9951 and 0.9989,respectively.The detection limits are 0.03?mol L-1,0.30?mol L-1and 0.10?mol L-1 for DA,UA and Tyr,respectively?S/N=3?.The different electrochemical behaviors of DA,UA and Tyr at various scan rates indicate that the electrode reaction of DA,UA and Tyr are adsorption-controlled processes at PHIMC/GCE.The application of PHIMC/GCE is demonstrated by simultaneous determinations of DA,UA and Tyr concentrations in human urine samples with satisfactory results.2.A poly 1H-imidazole-4-carboxylic acid?PHIMC?modified glassy carbon electrode?GCE?pre-coated with zinc oxide?ZnO?nanoparticle?PHIMC-ZnO/GCE?had been fabricated and used for simultaneous detection of ascorbic acid?AA?,dopamine?DA?,and uric acid?UA?.The surface morphology and electrochemical activity of the modified electrode were investigated by scanning electron microscopy?SEM?and electrochemical methods.The electrochemical behaviors of AA,DA,and UA on the modified electrode were investigated by cyclic voltammetry?CV?and differential pulse voltammetry?DPV?.The results show that modified electrode exhibits strong electro-catalytic activities toward oxidations of AA,DA and UA in a PBS buffer solution?pH=7.0?.Compared with those at PHIMC/GCE and ZnO/GCE,the current responses in anodic peak signal remarkably increase and the peak potential separation is 0.14 V at PHIMC-ZnO/GCE,which can be used for the simultaneous determinations of AA,DA and UA in their mixture with high sensitivity.Under the optimum conditions,the linear concentration dependences of DPV current responses were observed for AA,DA,and UA in the molar concentration ranges of 80-1400,0.15-45.00 and 2-120?mol·L-1.The detection limits?S/N=3?of AA,DA,and UA are 0.50,0.03,and 0.09?mol·L-1,respectively.And also,the different electrochemical behaviors of AA,DA,and UA at PHIMC-ZnO/GCE under various scan rates indicate that the electrode reaction of AA,DA,and UA is an adsorption-controlled process.The PHIMC-ZnO/GCE has been applied for the simultaneous determination of AA,DA,and UA in human urine and serum samples with satisfactory results.3.A poly?1H-imidazole-4-carboxylic acid??PHIMC?modified glassy carbon electrode?GCE?which had been pre-coated with carboxylic acid groups functionalized multiwalled carbon nanotubes?MWCNT??PHIMC-MWCNT/GCE?had been fabricated and used for simultaneous detection of uric acid?UA?,xanthine?XN?and hypoxanthine?HXN?.Scanning electron microscopy?SEM?,cyclic voltammetry?CV?and differential pulse voltammetry?DPV?techniques had been used to characterize the surface morphology and electrochemical characterization of the PHIMC-MWCNT/GCE composite film.Due to the special characteristics of the nanostructured MWCNT and the PHIMC film,the PHIMC-MWCNT/GCE exhibited high electrocatalytic activity,good selectivity and sensitivity for the simultaneous determination of UA,XN and HXN in a PBS buffer solution?pH=7?.The separations of anodic peak potentials of UA-XN and XN-HXN at this modified electrode were0.38V and 0.35V using DPV,respectively.Under the optimum conditions,the calibration curves for UA,XN and HXN were obtained in the range of 2.0-600,1.0-340 and 2.0-500?mol L-1.The detection limits?S/N=3?of UA,XN and HXN are 0.02?mol L-1,0.10?mol L-11 and 0.25?mol L-1,respectively.Due to the good selectivity and sensitivity,the composite film modified electrode had been applied to the simultaneous determination of AA,DA and UA in human urine and serum samples with satisfactory results. |
PDF Full Text Request