Simultaneous Determination Of Ascorbic Acid, Dopamine, Uric Acid And Nitrite-based Polymer Film Modified Electrodes

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 ofmental illness, infertility and AIDS due to its anti-oxidation. Dopamine (DA) is one ofthe important catecholamine neurotransmitters in the mammalian central nervoussystem, and it is widely applied to the treatment of circulatory collapse syndromecaused by the myocardial infarction, trauma, endotoxin sepsis, cardiac surgery orcongestive cardiac failure. Uric acid (UA), a primary end product of purinemetabolism, its abnormal level is commonly a symptom of some diseases, likehyperpiesia, leukemia and pneumonia. Nitrite (NO2?), a precursor to carcinogenicnitrosamines, is important within environmental, food and physiological systems, andits excessive level in blood will result in haemoglobin oxidation. Moreover, it couldenhance or inhibit the release of DA. It is nearly impossible to determine DA, UA andNO2? selectively or simultaneously at bare electrodes due to the weak andoverlapped oxidation waves and the electrode fouling caused by the adsorption oftheir oxidation products, which can lead to the poor sensitivity and selectivity. Hence,the development of sensitive and selective biosensors for their selective orsimultaneous detection is highly desirable for analytical applications and alsodiagnostic researches.To overcome these problems, various modified electrodes have beenconstructed and used to selectively or simultaneously determine AA, DA, UA andNO2?. Conjugated polymers always have irreplaceable position in theelectrochemical academic circles due to their numerous advantages, such as strongselective, good stability, high repeatability, and the thickness of the electrode surfacecan be controlled. Recently, thiazole-based polymers also gradually got people’sattention due to their unexceptionable selectivity and sensitivity.In order to make full use of the good properties of the different polymers,two different polymers were polymerized to the electrode surface step orsimultaneously. With this method, the process of preparation of modified electrodes is very simple. In addition, the obtained polymer film modified electrodes not onlyexhibit good selectivity, high sensitivity but also show a wide detection range for thedetermination of AA, DA, UA and NO2?.This paper includes three aspects as followed:1.3-dimensional (3D) non-periodic polyaniline (PAN) network has beenprepared via electrochemical polymerization of aniline on poly (o-aminophenol)(POAP) functionalized glassy carbon electrode (GCE) using a three-stepelectrochemical deposition procedure, and is applied to the simultaneousdetermination of AA and UA. Scanning electron microscopy (SEM), electrochemicalimpedance spectroscopy (EIS) and cyclic voltammetry (CV) have been employed toinvestigate the PAN network structure on a POAP modified GCE (PAN-OAP/GCE),which indicated the formation of a3D non-periodic PAN network with good electricalcontract and the maintenance of the electro-activity of PAN in neutral and even inalkaline media. Because of its unlike catalytic effect towards the oxidation of AA andUA, PAN-OAP/GCE could resolve the overlapped voltammetric response of AA and UAinto two sharp and well-de?ned voltammetric peaks with both CV and differentialpulse voltammetry (DPV). Hence, it could be applied for the selective andsimultaneous determination of AA and UA in their binary mixture. Under theoptimum conditions, the calibration curves for AA and UA are in the range of2.5-6,200μmol L-1and0.5-450μmol L-1with correlation coef?cients of0.9980and0.9980, respectively. The detection limits (S/N=3) are1.4and0.3μmol L-1for AAand UA, respectively. Besides good stability and reproducibility, the PAN-OAP/GCEalso exhibited good sensitivity and selectivity. The proposed method has beenapplied to the simultaneous detection of AA and UA in human urine with satisfactoryresult.2. A poly (2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole (APT)) modifiedglassy carbon electrode (GCE)(PAPT/GCE) is fabricated by electropolymerization ofAPT and used for the simultaneous detection of DA, UA and NO2?. It shows that thePAPT/GCE not only exhibites electrocatalytic activities towards the oxidation of DA,UA and NO2? but also could resolve the overlapped voltammetric signals of DA,UA and NO2? at bare GCE into three strong and well-defined oxidation peaks withenhanced current responses.The peak potential separations are130mV for DA–UAand380mV for UA–NO2? using DPV, which are large enough for the simultaneousdeterminations of DA, UA and NO2?. Under the optimal conditions, the anodic peakcurrents were correspondent linearly to the concentrations of DA, UA and NO2? inthe ranges of0.95-380μmol L?1,2.0-1,000μmol L?1and2.0-1,200μmol L?1for DA,UA and NO2?, respectively. The correlation coefficients were0.9989,0.9970and0.9968, and the detection limits (S/N=3) were0.2,0.35and0.6μmol L?1for DA, UAand NO2?, respectively. In0.1mol L?1PBS pH5.0, the PAPT film exhibited goodelectrochemical activity, showing a surface-controlled electrode process with theapparent heterogeneous electron transfer rate constant (ks) of25.9s?1and thecharge–transfer coefficient (α) of0.49, and thus displayed the features of anelectrocatalyst. Besides the good stability and reproducibility of the PAPT/GCE, thePAPT/GCE also exhibited good sensitivity, excellent selectivity and a wide detectionrange. The PAPT/GCE had been used for the simultaneous detection of DA, UA andNO2? with all-right result.3. A thiazole-based copolymer (PATA-AMT) has been synthesized byelectrochemical copolymerization of2-amino-4-thiazoleacetic acid (ATA) and3-amino-5-mercapto-1,2,4-triazole (AMT) on glassy carbon electrode (GCE), and itwas used for the simultaneous detection of DA, UA and NO2?. The copolythiazolefilm (PATA-AMT) modified GCE (PATA-AMT/GCE) not only exhibits electro-catalyticeffects towards the oxidations of DA, UA and NO2? but also can resolve the weak andoverlapped voltammetric responses of DA, UA and NO2? into three strong andwell-de?ned voltammetric peaks in0.1mol L-1phosphate buffer solution (PBS, pH6.0). Under the optimum conditions, the linear concentration dependences of theDPV current responses are observed for DA, UA and NO2? in the concentrationranges of0.85–390μmol L-1,1.95–1,200μmol L-1and2.0–1,240μmol L-1with thecorrelation coefficients of0.9993,0.9993and0.9977, respectively. The detectionlimits are0.2μmol L-1,0.25μmol L-1and0.5μmol L-1for DA, UA and NO2?,respectively (S/N=3). The different electrochemical behaviors of DA, UA and NO2? at various scan rates indicate that the electrode reaction of DA is anadsorption-controlled process, and those of UA and NO2? are diffusion-controlledprocesses at PATA-AMT/GCE. The practical application of the modified electrode hasbeen investigated by the simultaneous determinations of DA, UA and NO2? in humanurine and serum samples by using standard adding method with satisfactory results.