Change of extracellular ascorbic acid in the brain cortex following ice water vestibular stimulation： an on-line electrochemical detection coupled with in vivo microdialysis sampling for guinea pigs

Background Ascorbic acid （AA） represents one of the most important enzyme co-factors, antioxidants and neuromodulators and plays an important role in the cerebral system. Increasing evidence has suggested that AA could treat certain kinds of vertigo diseases such as Meniere＇s disease. To elucidate the neurochemical functions associated with AA in vertigo, the change of extracellular AA in the brain cortex following caloric vestibular stimulation （CVS） was evaluated.Methods An on-line electrochemical detection was coupled with in vivo microdialysis to continuously monitor the change of extracellular AA in the primary somatosensory （SI） area of guinea pigs following a caloric vestibular stimulation. Sixteen guinea pigs were divided into three groups, i.e., experimental group with irrigation of the ear canal with ice water （0℃） （n=-8）, and two control groups, one with irrigation of the ear canal with warm water （38℃） （n=-4） and the other with irrigation of the auricle with ice water （n=-4）.Results In the experimental group, the ice water irrigation of the left external ear canal induced a horizontal nystagmus towards the right side lasting about 45 seconds. No nystagmus was induced by warm water irrigation of the external ear canal or by ice water irrigation of the auricle. The extracellular AA concentration significantly increased following the ice water vestibular stimulation, reaching a maximum of （130±20）% （n=8） of the basal dialysate level （2.61±0.92） μmol/L （n=8）, lasting at least for an hour. AA level did not change distinctly after the irrigation of the left external ear canal with warm water or the irriclation of the auricle with ice water.Conclusions The concentration of extracellular AA in the brain cortex of the SI area increased following the ice water vestibular stimulation. This demonstration may be useful for the investigation of the neurochemical processes associated with AA in the process of vertigo.

Electrochemically reduced graphene oxide with enhanced electrocatalytic activity toward tetracycline detection

An electrochemically reduced graphene oxide sample, ERGO_0.8v, was prepared by electrochemical reduction of graphene oxide （GO） at -0.8 V, which shows unique electrocatalytic activity toward tetracycline （TTC） detection compared to the ERGO-12v （GO applied to a negative potential of-1.2 V）, GO, chemically reduced GO （CRGO）-modified glassy carbon electrode （GC） and bare GC electrodes. The redox peaks of TTC on an ERGO-0.8v-modifled glass carbon electrode （GC/ERGO-0.8v） were within 0-0.5 V in a pH 3.0 buffer solution with the oxidation peak current correlating well with TTC concentration over a wide range from 0.1 to 160 mg/L Physical characterizations with Fourier transform infrared （FT-IR）, Raman, and X-ray photoelectron spectroscopies （XPS） demonstrated that the oxygen-containing functional groups on GO diminished after the electrochemical reduction at -0.8 V, yet still existed in large amounts, and the defect density changed as new sp2 domains were formed. These changes demonstrated that this adjustment in the number of oxygen-containing groups might be the main factor affecting the electrocatalytic behavior of ERGO. Additionally, the defect density and sp2 domains also exert a profound influence on this behavior. A possible mechanism for the TTC redox reaction at the GC/ERGO-0.8v electrode is also presented. This work suggests that the electrochemical reduction is an effective method to establish new catalytic activities of GO by setting appropriate parameters.

Determination of atmospheric hydroxyl radical by HPLC coupled with electrochemical detection

The hydroxyl radical （·OH） plays a central role in the oxidation and removal of many atmospheric compounds. Measurement of atmospheric ·OH is very difficult because of its high reactivity and low atmospheric abundance. In this article, a simple and highly sensitive method, high performance liquid chromatography coupled with coulometric detection （HPLC-CD）, was developed to determine ·OH indirectly by determining its reaction products with salicylic acid （SAL）, 2,3-dihydroxybenzoic acid （2,3-DHBA）, and 2,5-dihydroxybenzoic acid （2,5-DHBA）. Under the optimum conditions for its determination, 2,3-DHBA and 2,5-DHBA could be well separated and the detection limits for 2,3-DHBA were 3 ×10^-10 mol/L and for 2,5-DHBA were 1.5 ×10^-10 mol/L, which were lower than most previous reports. This method was also applied to measure atmospheric hydroxyl radical levels and demonstrated the feasibility in clean and polluted air.

Determination of Nicotine in Tobacco by Capillary Electrophoresis with Electrochemical Detection

A sensitive, simple and low-cost method based on capillary electrophoresis（CE） with electrochemical（EC） detection at a carbon fiber microdisk electrode（CFE） was developed for the determination of nicotine. Effects of de- tection potential, concentration and pH value of the phosphate buffer, and injection time as well as separation voltage were investigated. Under the optimized conditions： a detection potential of 1.20 V, 40 rnmol/L phosphate buffer（pH 2.0）, a sample injection time of 10 s at 10 kV and a separation voltage of 16 kV, the linear range obtained was from 5.0×10^-7 mol/L to 1.0×10^-4 mol/L with a correlation coefficient of 0.9989 and the limit of detection（LOD, S/N=3） obtained was 5.0×10^-8 mol/L. The method was also used to determine the nicotine in cigarettes. Nicotine amount ranged from 0.211 mg/g to 0.583 mg/g in the pipe tobacco of seven brands of cigarette and the amount in one ciga- rette varied from 0.136 mg/cigarette to 0.428 mg/cigarette.

Analysis of Amino Acids in a Single Human Red Blood Cell by Capillary Zone Electrophoresis with Intracellular NDA- derivatization and Electrochemical Detection

A novel method for determination of amino acids in individual human red blood cells has been developed. In this method, the derivatization reagents (NDA and CN-) are introduced into living cells by electroporation. After completion of derivatization, the amino acids in a single cell is determined by capillary zone electrophoresis with end-column amperometric detection.

A MXene-functionalized paper-based electrochemical immunosensor for label-free detection of cardiac troponin I

Convenient,rapid,and accurate detection of cardiac troponin I(cTnI)is crucial in early diagnosis of acute myocardial infarction(AMI).A paper-based electrochemical immunosensor is a promising choice in this field,because of the flexibility,porosity,and cost-efficacy of the paper.However,paper is poor in electronic conductivity and surface functionality.Herein,we report a paper-based electrochemical immunosensor for the label-free detection of cTnI with the working electrode modified by MXene(Ti_(3)C_(2))nanosheets.In order to immobilize the bio-receptor(anti-cTnI)on the MXene-modified working electrode,the MXene nanosheets were functionalized by aminosilane,and the functionalized MXene was immobilized onto the surface of the working electrode through Nafion.The large surface area of the MXene nanosheets facilitates the immobilization of antibodies,and the excellent conductivity facilitates the electron transfer between the electrochemical species and the underlying electrode surface.As a result,the paper-based immunosensor could detect cTnI within a wide range of 5-100 ng/mL with a detection limit of 0.58 ng/mL.The immunosensor also shows outstanding selectivity and good repeatability.Our MXene-modified paper-based electrochemical immunosensor enables fast and sensitive detection of cTnI,which may be used in real-time and cost-efficient monitoring of AMI diseases in clinics.

Recent Advance in the Electrochemical Detection of Sulphide and Sulphhydryl Species

This article aims at providing a critical review of some most recent developments in the electrochemical detection and measurement of hydrogen sulphide and the related species, which are of great significance to a variety of industries and in environmental moitoring. The molecular recognition processes are initiated by using either an organic precursor or a catalytic complex, leading to extensive ranges of detection. A series of advanced chemical and simulation techniques are used to probe the mechanistic details of the analytical chemistry involved.

Assay of Histamine in Single Mast Cells by Capillary Zone Electrophoresis with Electrochemical Detection

Capillary zone electrophoresis was employed for the analysis of histamine in single rat peritoneal mast cells using an amperometric detector. In this method, individual mast cells and then 0.02 mol/L NaOH as a lysing solution are injected into the front end of the separation capillary. A cell injector was constructed for easy injection of single cells. Histamine in single mast cells has been identified and quantified.

Electrochemical Detection of Alkaline Phosphatase in BALB/c Mouse Fetal Liver Stromal Cells with Capillary Electrophoresis

A method for determination of alkaline phosphatase (ALP) in BALB/c mouse fetal liver stromal cells has been described based on the catalytic reaction. After the cell extract is incubated with the substrate disodium phenyl phosphate, the reaction product phenol generated by ALP is determined by capillary electrophoresis with electrochemical detection.

Rapid Determination of Dopamine and Its Metabolites During in vivo Cerebral Microdialysis by Routine High Performance Liquid Chromatography With Electrochemical Detection

To determine dopamine and its metabolites during in vivo cerebral microdialysis by routine high performance liquid chromatography with electrochemical detection. Methods Microdialysis probes were placed into the right striatum of Wistar rat brains and perfused with Ringer＇s solution at a rate of 1.5 pL/min. A reverse phase HPLC with electrochemistry was used to assay DA, DOPAC, and HVA after cerebral microdialysates were collected every 20 minutes from awake and freely moving rats. In order to identify the reliability of this method, its selectivity, linear range, precision and accuracy were tested and the contents of DA, DOPAC, and HVA in rat microdialysates were determined. Results The standard curve was in good linear at the concentration ranging from 74 nmol/L to 1.5 pmol/L for DOPAC （r^2= 0.9996）, from 66 nmol/L to 1.3 gmol/L for DA （r^2=l.0000） and from 69 nmol/L to 1.4 pmol/L for HVA （r^2=0.9992）. The recovery of DOPAC （0.30, 0.77, 1.49 gmol/L）, DA （0,26, 0.69, 1.32 gmol/L）, and HVA （0.27, 0.71, 1.37 gmol/L） was 82.00±1.70%, 104.00±4.00%, 98.70±3.10%; 92.30± 1.50%, 105.30±2.30%, 108.00±2.00%; 80.00±7.80%, 107.69±8.00%, and 108.66±3.10%, respectively at each concentration. Their intra-day RSD was 3.3%, 3.4%, and 2.5%, and inter-day RSD was 4.2%, 2.3%, and 5.6%, respectively. The mean extracellular concentrations of DOPAC, DA, and HVA in rat brain microdialysates were 10.7, 2.4, and 9.2 gmol/L （n=6）, respectively. Conclusion The findings of our study suggested that the simple, accurate and stable method can be applied to basic researches of diseases related to monoamines neurotransmitters by cerebral microdialysis in rats.

Extraordinary tunable dynamic range of electrochemical aptasensor for accurate detection of ochratoxin A in food samples

We report the design of a sensitive,electrochemical aptasensor for detection of ochratoxin A(OTA)with an extraordinary tunable dynamic sensing range.This electrochemical aptasensor is constructed based on the target induced aptamer-folding detection mechanism and the recognition between OTA and its aptamers results in the conformational change of the aptamer probe and thus signal changes for measurement.The dynamic sensing range of the electrochemical aptasensor is successfully tuned by introduction of free assistant aptamer probes in the sensing system.Our electrochemical aptasensor shows an extraordinary dynamic sensing range of 11-order magnitude of OTA concentration from 10^−8 to 10^2 ng/g.Of great significance,the signal response in all OTA concentration ranges is at the same current scale,demonstrating that our sensing protocol in this research could be applied for accurate detections of OTA in a broad range without using any complicated treatment of signal amplification.Finally,OTA spiked red wine and maize samples in different dynamic sensing ranges are determined with the electrochemical aptasensor under optimized sensing conditions.This tuning strategy of dynamic sensing range may offer a promising platform for electrochemical aptasensor optimizations in practical applications.

Separation and Determination of Methylnaltrexone in Human Plasma Samples After Oral Administration by HPLC Coupled with Electrochemical Detection

A high performance liquid chromatography(HPLC) method coupled with electrochemical detection and solid phase extraction is described for the separation and determination of methylnaltrexone(MNTX), a quaternary opioid antagonist, in human clinical plasma samples after oral administration. Linearity of the standard curve for MNTX was found in the range of 4.0_150 ng/mL and was statistically conformed. The correlation coefficient(r2) and calibration equation obtained from linear regression analysis are 0.9999 and Y=54.27X-0.22, where Y and X represent the peak area and concentration of MNTX, respectively. The detection limit of MNTX under the present experimental conditions is 2.0 ng/mL by estimating at a ratio of 3 of signal to noise. The mean recovery of MNTX in human plasma is higher than 97%. The analytical method was applied to the pharmacokinetic determination of MNTX after single dose oral administration. These data demonstrate that the change of MNTX plasma concentration versus time is obvious. MNTX level of plasma reaches to a plateau between 45 to 120 minutes and then falls slowly. The content of MNTX in plasma sample maintains at an obviously detectable level after twelve hours of oral administration. The pharmacokinetic parameters for a single dose of 19.2 mg/kg in plasma are c_~max =206.42(±16.53) ng/mL and t_~max =60 min.

Determination of Amino Acids in Single Human Lymphocytes after On-capillary Derivatization by Capillary Zone Electrophoresis with Electrochemical Detection

Amino acids in individual human lymphocytes were determined by capillary zone electrophoresis with electrochemical detection after on-capillary derivatization. In order to inject cells easily, a cell injector was designed. Four amino acids (serine, alanine, taurine, and glycine) in single human lymphocytes have been identified. Quantitation has been accomplished through the use of calibration curves.

Analysis of Ascorbic Acid in Single Human Neutrophils by Electrochemical Detection

Ascorbic acid in individual human neutrophils was determined by capillary zoneelectrophoresis with electrochemical detection. In order to overcome the influence of theadsorption of the substances in cells on the inner surface wall of the capillary on the migration time and the number of theoretical plates, a procedure for treating capillaries has been described.

Monitoring Homovanillic Acid and Vanillylmandelic Acid in Human Urine by Capillary Electrophoresis with Electrochemical Detection

A simple, rapid and low-cost method of separation and determination of homovanillic acid and vanillylmandelic acid in human urine was developed based on capillary zone electrophoresis / amperometric detection with high sensitivity and good resolution.

On-line Chatter Detection Using an Improved Support Vector Machine

On-line chatter detection can avoid unstable cutting through monitoring the machining process.In order to identify chatter in a timely manner,an improved Support Vector Machine(SVM)is developed in this paper,based on extracted features.In the SVM model,the penalty factor(e)and the core parameter(g)have important influence on the classification,more than from Kernel Functions(KFs).Hence,first the classification results are conducted using different KFs.Then two methods are presented for exploring the best parameters.The chatter identification results show that the Genetic Algorithm(GA)approach is more suitable for deciding the parameters than the Grid Explore(GE)approach.

Quality Analysis of Herbal Medicine Products Prepared from Herba Sarcandrae by Capillary Electrophoresis with Electrochemical Detection

A capillary electrophoresis with electrochemical detection（CE-ED） method was developed for the quality analysis of herbal medicine products prepared from the same herb of Herba Sarcandrae： Fufang Caoshanhu tablets, Qingrexiaoyanning capsules, and Xuekang oral liquids. Under the optimal analysis conditions, the low detection limit[l.0×10^-7 mol/L（S/N=3）] and the wide linear range（1.0×10^-7-1.0×10^-4 mol/L） were obtained for quality standard compound of isofraxidin. The precisions of the peak current and the migration time（as RSDs） for the real sample analysis were 2.0%-2.6%, and 1.2%-1.8% for isofraxidin, respectively. The contents of isofraxidin detected were 15.77 μg/tablet, 0.48 mg/capsule, 1.2 mg/ampoule（Jiangxi）, and 0.44 mg/ampoule（Dalian） for Fufang Caoshanhu tablets, Qingrexiaoyanning capsules, and Xuekang oral liquids from different manufacturers, respectively. Quality estimate was conducted by comparing the contents of isofraxidin in the herbal medicine products with the demanded values of Chinese pharmacopeia. In addition, based on their own unique CE-ED profiles（namely, CE-ED electropherograms） the Xuekang oral liquids from the different manufacturers could be easily identified.

Electrochemical Detection of Horseradish Peroxidase at Zeptomole Level

An electrochemical method for determination of horseradish peroxidase (HRP) was developed using a capillary catalytic system. HRP can be measured in several minutes with a detection limit of 4.8 x 10(-12) mol/L or 47 zmol (S/N=3).

Plasma Activation of Integrated Carbon Nanotube Electrodes for Electrochemical Detection of Catechol

In this study, integrated multi-wall carbon nanotube （MWCNT） electrodes were prepared in the holes of glass directly by microwave plasma chemical vapour deposition （MWPCVD）. The electrochemical behaviour of catechol at the integrated MWCNT electrodes was investigated. The oxygen plasma treated CNT electrodes had better electrochemical performance for the analysis of catechol than that of as-synthesized CNT electrodes. Both the as-synthesized CNTs and plasma treated CNTs were characterized by TEM（transmission electron microscopy, XPS（X-ray photoelectron spectroscopy） and Raman spectroscopy. The results revealed that the oxygen plasma activation is an effective method to enhance the electrochemical properties of CNT electrodes.

A New Dual-electrode and Multi-channel Electrochemical Detection System for Capillary Electrophoresis

A new type of dual-electrode and multi-channel electrochemical detection technology for capillary electrophoresis is described in this paper. Two detectors(the amperometric detector and the conductometric detector) or two conductometric detectors are connected to the same capillary electrophoresis system. The whole system possesses the advantages of the two electrochemical detectors including sparing time, improving the analytical speed and expanding the sample range. The working electrode and detector cell are handled easily. The system was applied to sample detection with satisfactory results.