Simultaneous detection of dopamine,ascorbic acid,and uric acid at electrochemically pretreated carbon nanotube biosensors

In this work we have evaluated the performance of electrochemically pretreated single-walled carbon nanotubes (SWCNTs) toward the electrochemical detection of dopamine in the presence of ascorbic acid and uric acid at physiological pH. Results indicated that the electrochemically pretreated SWCNTs showed a selective and enhanced electroanalytical response with minimal electrode fouling toward the detection of dopamine than their untreated counterparts. The observed behavior is attributed to the negatively charged layer present on the SWCNTs originating from the rupture of the basal plane present on the end caps following electrochemical pretreatment. The rupture of basal plane is evident from surface Raman measurements. The negatively charged surface selectively allows the cationic dopamine toward the electrode and repels the anionic ascorbate and uric acid when they coexist in the same solution under physiological pH. A limit of detection of about 15 nM is obtained with these electrodes for the detection of dopamine in the presence of ascorbic acid and uric acid.From the Clinical EditorThe performance of electrochemically pretreated single-walled carbon nanotubes (SWCNTs) was studied toward the electrochemical detection of dopamine. These SWCNTs showed a selective and enhanced response toward the detection of dopamine. A limit of detection of about 15 nM is obtained with these electrodes for the detection of dopamine in the presence of ascorbic acid and uric acid.     

The metabolism of supplementary vitamin C during the common cold.

Ascorbic acid concentrations have been measured in leukocytes and plasma following oral administration of 2000 mg vitamin C in the same subjects while they had cold symptoms and after recovery from their colds. Plasma and leukocyte concentrations rose significantly in females, but only plasma concentrations rose in males, after the loading dose during colds. In the postcold tests, only plasma concentrations rose in both sexes. There was a significant difference in plasma leukocyte regression coefficients between the cold and postcold tests in females. Ascorbic acid passes into the plasma for metabolic purposes, and its storage is less in the leukocytes, during colds. Males had worse colds than females because their catarrhal symptoms were more severe. Higher tissue concentrations of ascorbic acid tended to be associated with low total, toxic, and catarrhal symptom values. A rise in tissue ascorbic acid was associated with less severe catarrhal symptoms in females. Ascorbic acid concentrations in the plasma and tongue were significantly higher after the subjects had recovered from their cold symptoms. Increasing the loading dose of vitamin C from 500 to 2000 mg more than doubled the leukocyte concentration of ascorbic acid in females. The higher dose enabled uptake of the vitamin into the leukocytes to take place over a 4-hour period. It did not give rise to increased uptake into male leukocytes. Administration of supplementary vitamin C elevated plasma ascorbic acid. The ascorbic acid then passed into the tissues depleted of vitamin C during the cold syndrome. A single supplementary dose of 2000 mg vitamin C can replete leukocyte ascorbic acid during a 4-hour period in females, but a larger dose may be necessary in males.     

Absorption of ascorbic acid from a film-coated tablet and from a new enteric-coated pellet preparation in subjects with inadequate plasma levels of ascorbic acid.

The effects of a film-coated tablet and a novel enteric-coated pellet preparation of ascorbic acid (CAS 50-81-7) on the plasma concentration and on the urinary excretion of ascorbic acid were investigated. The pharmacokinetic properties of these dosage forms were also compared both after a single dose and in steady state. The study was carried out as a randomized, single blind parallel group trial in 11 volunteers with inadequate plasma levels of ascorbic acid. The duration of the treatment period was 7 days. After the first dose, higher plasma ascorbic acid concentration as well as AUC and Cmax values were achieved with the film-coated preparation. After the multiple dosing in steady state, plasma ascorbic acid concentration as well as AUC and Cmax values were higher with the new pellet preparation. In addition, the plasma ascorbic acid concentration remained on higher level with pellet preparation on the 7th day. Tmax values for the pellet preparation were also slightly higher on both of the pharmacokinetic test days. The amount of ascorbic acid excreted in urine was higher with the film-coated tablet. According to the results of this study it can be supposed that during the long-term supplementation the more complete absorption can be achieved with the new enteric-coated pellet preparation.     

Differential pulse-voltametric determination of dopamine using pretreated electrochemical electrodes

The electroanalytical method proposed permits a sensitive and selective determination of dopamine in the presence of ascorbic acid applying a fast galvanostatic pretreatment of the carbon electrodes. The effect of the electrochemical pretreatment at glassy carbon electrode (A = 0.8 mm2) was compared with that of carbon fibre array electrode (A = 0.15 mm2). Both types of electrodes showed approximately the same detection limit for dopamine of about 1.10(-7) mol/l dopamine. In comparison to the polished electrodes the sensitivity is improved by a factor of 100. The galvanostatic pretreatment led also to a drastic improvement of selectivity by cathodic shift of the ascorbic acid peak potential.     

The microencapsulated ascorbic acid release<Emphasis Type="Italic">in vitro</Emphasis> and its effect on iron bioavailability

The present study was carried out to examine the stability of microencapsulated ascorbic acid in simulated-gastric and intestinal situation in vitro and the effect of microencapsulated ascorbic acid on iron bioavailability. Coating materials used were polyglycerol monostearate (PGMS) and medium-chain triacylglycerol (MCT), and core materials were L-ascorbic acid and ferric ammonium sulfate. When ascorbic acid was microencapsulated by MCT, the release of ascorbic acid was 6.3% at pH 5 and 1.32% at pH 2 in simulated-gastric fluids during 60 min. When ascorbic acid was microencapsulated by PGMS, the more ascorbic acid was released in the range of 9.5 to 16.0%. Comparatively, ascorbic acid release increased significantly as 94.7% and 83.8% coated by MCT and PGMS, respectively, for 60 min incubation in simulated-intestinal fluid. In the subsequent study, we tested whether ascorbic acid enhanced the iron bioavailability or not. In results, serum iron content and transferring saturation increased dramatically when subjects consumed milks containing both encapsulated iron and encapsulated ascorbic acid, compared with those when consumed uncapsulated iron or encapsulated iron without ascorbic acid. Therefore, the present data indicated that microencapsulated ascorbic acid with both PGMS and MCT were effective means for fortifying ascorbic acid into milk and for enhancing the iron bioavailability.     

Separation of aceclofenac and diclofenac in human plasma by free zone capillary electrophoresis using N-methyl-D-glucamine as an effective electrolyte additive.

Aceclofenac (A) and diclofenac (D) are effective non-steroidal anti-inflammatory drugs (NSAIDs) derived from the phenylacetic acid with pronounced antirheumatic, anti-inflammatory, analgesic and antipyretic properties. Our work proposes a new, fast-free zone capillary electrophoresis method for the simultaneous determination of aceclofenac and diclofenac in human plasma. The effect of increasing concentrations of N-methyl-D-glucamine organic base on borate run buffer was investigated. A good separation was achieved using a 40 cm x 75 microm uncoated silica capillary, 300 mmol/l sodium borate buffer, 200 mmol/l N-methyl-D-glucamine, pH 8.9, in about 3 min. Moreover, the plasma sample pre-treatment procedure was examined: acidic precipitants such as trichloroacetic acid (TCA), metaphosphoric acid (MPA), perchloric acid (PCA) or 5-sulphosalicylic acid (SSA) cause a total loss of analytes while acetonitrile allows a recovery of 97-98% of both compounds. Its simplicity and rapidity and the low analysis costs demonstrate that our method is a reliable and efficient mean for the comprehensive determination of aceclofenac and diclofenac in human plasma when pharmacokinetics studies are required.     

Automatic potentiometric flow titration procedure for ascorbic acid determination in pharmaceutical formulations

A flow procedure for the determination of ascorbic acid in pharmaceutical formulations exploiting potentiometric titration is described. The method is based on the reduction of IO₃⁻ by ascorbic acid and the detection was carried out employing a flow-through ion selective electrode for iodide. The flow network controlled by a microcomputer was designed to implement multicommutation for ease of operation and robustness. The titration system allowed the determination of ascorbic acid in pharmaceutical formulations with concentrations ranging from 7.5 to 15.0 mmol l⁻¹. No significant differences at the 95% confidence level were observed in comparison with results obtained by a manual procedure. Merit figures of results such as a relative standard deviation of 1.0% (n=6) and a reagent consumption of 21.4 mg IO₃⁻ per determination were obtained.     

A rapid and selective solid-phase UV spectrophotometric method for determination of ascorbic acid in pharmaceutical preparations and urine

Ascorbic acid was determined by a solid-phase UV spectrophotometry technique through the sorption of this on a dextran-type anion-exchange resin, Sephadex QAE A-25 and posterior direct measurement of its absorbance on the resin at 267 and 400 nm, packed in a 1-mm cell. The calibration graph was linear over the range 0.3-5.0 microg ml(-1). The sensitivity obtained is more than 50 times higher than that of the corresponding solution method. The detection limit was 0.05 microg ml(-1) and the relative standard deviation 0.74% (n = 10). This method is very rapid and highly selective for determining ascorbic acid in the presence of other species absorbing in the ultraviolet region and which are normally encountered with it. The one-step method proposed was successfully applied in the determination of ascorbic acid in pharmaceutical preparations and urine and the results were of comparable accuracy as indicated by a statistical analysis of the data, using both t- and F-tests.     

Vitamin C metabolism and the common cold

Summary Male and female university students at the commencement of common cold symptoms were given a single dose of 500 mg of vitamin C. Plasma and leucocyte ascorbic acid concentrations were then measured for six hours. Symptom severity was recorded. The test was repeated twenty-three days after the last symptom had disappeared. The ascorbic acid blood response curve had then returned to normal. Significant and similar elevations of plasma ascorbic acid occurred in both sexes in the cold and post-cold tests. The leucocyte response was significantly reduced in the males but was unaffected in the females in the cold test. The regression coefficients between leucocyte and plasma values (P/L regressions) confirmed that ascorbic acid metabolism was less deranged in females than males during the cold test. Administration of ascorbic acid was associated with increases in blood ascorbic acid concentrations during the post-cold period but not during colds. A single dose of 1000 mg raised blood ascorbic acid concentrations in both sexes during their colds. The elevation was higher, and maintained for two hours longer in the females.In vitro incubation of leucocytes in ascorbic acid confirmed that their ascorbic acid load could be increased by approximately 100% while cold symptoms were present. A significant association between cold symptoms and the state of ascorbic acid metabolism was demonstrated by correlating the ratio of toxic to catarrhal symptoms with P/L regressions during colds. When catarrhal symptoms are severe, ascorbic acid passes from the leucocytes into the plasma, and thence into the inflamed respiratory membranes. When toxic symptoms are relatively more severe, ascorbic acid is retained in the cells. The beneficial effect of vitamin C on the common cold is associated with its influence on ascorbic acid metabolism. A sex-linked difference in ascorbic acid metabolism is manifested during the common cold which affects assessment of the effects of vitamin C on the common cold.     

Therapeutic review: is ascorbic acid of value in chromium poisoning and chromium dermatitis?

INTRODUCTION: Repeated topical exposure to chromium(VI) may cause an allergic contact dermatitis or the formation of chrome ulcers. Systemic toxicity may occur following the ingestion of a chromium(VI) salt, from chromium(VI)-induced skin burns, or from inhalation of chromium(VI) occurring occupationally. Soluble chromium(VI) salts are usually absorbed more easily and cross cell membranes more readily than trivalent chromium salts, and, therefore chromium(VI) is more toxic than chromium(III). In experimental studies, endogenous ascorbic acid in rat lung, liver, and kidney and human plasma, effectively reduces chromium(VI) to chromium(III). The administration of exogenous ascorbic acid has been advocated therefore in the treatment of systemic chromium poisoning and chromium dermatitis to enhance the extracellular reduction of chromium(VI) to the less bioavailable chromium(III). REVIEW: In vitro experiments confirm that the addition of ascorbic acid to plasma containing chromium(VI) leads to a dose-dependent reduction of chromium(VI) to chromium(III). In animal studies, parenteral ascorbic acid 0.5-5 g/kg significantly reduced chromium-induced nephrotoxicity when administered 30 minutes before parenteral sodium dichromate and up to 1 hour after parenteral sodium chromate dosing. Parenteral ascorbic acid 0.5-5 g/kg also reduced mortality when given orally up to 2 hours after oral potassium dichromate dosing. However, the administration of parenteral ascorbic acid more than 2 hours after parenteral chromate in these experimental studies did not protect against renal damage, and parenteral ascorbic acid given 3 hours postparenteral chromate increased toxicity. In addition, there is no confirmed clinical evidence that the administration of ascorbic acid lessens morbidity or mortality in systemic chromium poisoning. A possible reason for the lack of benefit of ascorbic acid when administration is delayed, is that chromium(VI) cellular uptake has occurred prior to ascorbic acid administration. Topical 10% ascorbic acid has been claimed to reduce significantly the healing time of experimentally induced chrome ulcers in guinea pigs. The proposed mechanism is reduction on the skin surface of chromium(VI) to chromium(III). Several case reports suggest that topical ascorbic acid is effective in the management of chromium dermatitis but this has not been confirmed in controlled clinical trials and, moreover, the practical difficulties of frequent application are likely to limit its usefulness. DISCUSSION: Based on experimental studies, substantial amounts of ascorbic acid would need to be administered, preferably parenterally, soon after exposure to prevent systemic toxicity from chromium(VI) in humans. However, as ascorbic acid is a metabolic precursor of oxalate, the administration of ascorbic acid in high dose could lead to acute oxalate nephropathy, particularly in the presence of renal failure. While smaller doses of ascorbic acid (e.g., 10 g intravenously) are not toxic, such doses probably will not reduce the mortality from systemic chromium poisoning. CONCLUSION: There is currently insufficient evidence to advocate the use of ascorbic acid in the management of systemic chromium toxicity. Topical ascorbic acid may reduce dermal hexavalent chromium exposure, but this observation must be confirmed in controlled studies.     

DNA strand breakage and oxygen tension: effects of beta-carotene, alpha-tocopherol and ascorbic acid.

DNA damage is involved in carcinogenesis, aging and other degenerative diseases. The relationship between DNA strand breakage and beta-carotene (0.1-1.6 microM) was examined under different O(2) tensions and with other antioxidants: alpha-tocopherol (5-80 microM), ascorbic acid (10-160 microM) and mixtures of these antioxidants. Supercoiled plasmid DNA pBR322 was incubated with 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) to induce DNA strand breaks in the presence of antioxidants under 15, 150, and 760 torr of O(2) tension. Under 15 torr of O(2) tension, beta-carotene, alpha-tocopherol, ascorbic acid and mixtures of these antioxidants provided a dose-dependent protection against AAPH-induced DNA strand breaks. The best protection was achieved in the mixture of antioxidants. Under 150 torr of oxygen tension, the antioxidant effect of beta-carotene was diminished at > or = 0.8 microM. A prooxidant effect was found at 0.8 > or = microM beta-carotene, producing more single- and double-strand breaks. alpha-Tocopherol and ascorbic acid exhibited dose-dependent antioxidant effects at 150 torr of oxygen tension. Under 760 torr of O(2) tension, the prooxidant effect of 0.8 microM beta-carotene was significant, causing supercoiled DNA to completely breakdown to circular and linear forms. In addition, 760 torr of O(2) tension attenuated the antioxidant effects of alpha-tocopherol and ascorbic acid. Thus, beta-carotene causes concentration-dependent DNA breakdown at high O(2) tension. The protection of DNA from the prooxidant effects of beta-carotene afforded by alpha-tocopherol and/or ascorbic acid was limited at high O(2) tension.     

抗坏血酸氯化钠注射液的制备及质量控制

目的:制备100mL装量抗坏血酸氯化钠注射液并建立其质量控制方法。方法:以抗坏血酸为主药制备注射液;采用紫外-可见分光光度法测定其中主药的含量。结果:所制制剂检查、鉴别等均符合2005年版《中国药典》相关规定;抗坏血酸检测浓度的线性范围为4.0～12.0μg·mL-1(r=0.9999);平均回收率为99.85%(RSD=0.75%,n=6)。结论:本制剂组方合理,制备工艺简单可行,质量稳定可控。     

Interaction of erythorbic acid with ascorbic acid catabolism

There exist altogether four stereoisomers of ascorbic acid. Erythorbic acid (D-isoascorbic acid) differs in the spatial configuration at carbon 5 and has less than 5 per cent of biological vitamin C activity. In guinea pigs, depending on an exogenous supply of ascorbic acid, a possible interaction of erythorbic acid with absorption, transport through the cell membranes at the tissue level, or with catabolism of ascorbic acid has been investigated. After oral administration, results suggest no difference in absorption of these two compounds from the intestine, whereas uptake by the tissues was approximately four to one in favour of ascorbic acid. Feeding experiments with erythorbic acid indicate the availability of ascorbic acid being diminished by 40-60% when administered together with erythorbic acid. Kinetic data on the catabolism of ascorbic acid showed a significant reduction in half-life (50% of the dose excreted) of the vitamin caused by administration of erythorbic acid. The results suggest the oxidative destruction of ascorbic acid in the liver being significantly accelerated. Thus, ingestion of erythorbic acid interacts with newly introduced ascorbic acid by enforcing the breakdown of ascorbic acid. Implications of these findings for the metabolism, availability and nutritional status of ascorbic acid in humans will be discussed.     

Enzymatic formation of ascorbic acid in liver homogenate of mice fed dietary ascorbic acid

The effect of exogenous ascorbic acid intake on enzymatic formation of ascorbic acid in mice has been studied. After the mice were on diets containing ascorbic acid for two months, the rates of ascorbic acid formation in mouse liver homogenates were measured in vitro using glucuronolactone and gulonolactone as substrate in their respective reaction systems. Exogenous ascorbic acid intake (1, 5 or 8% in the diet) was able to reduce activities of ascorbic acid synthesizing enzymes in mouse liver in either the glucuronolactone or gulonolactone system. The control mechanism for reaction of glucuronolactone to produce ascorbic acid is not stereospecific because large amounts of dietary erythorbic acid, a stereoisomer of ascorbic acid, could also reduce the rate of ascorbic acid formation when glucuronolactone was used as substrate. However, the regulation of ascorbic acid synthesis using gulonolactone as a precursor was apparently stereospecific. Dietary glucose or xylitol had no effect on activities of ascorbic acid synthesizing enzymes.     

口服维生素C对人眼房水中抗坏血酸盐浓度的影响

AIM: To study oral administration of vitamin C on human aqueous humour ascorbate concentration. METHODS: High performance liquid chromatography (HPLC) coupled with electrochemical detector (ECD) was used. The effect of oral administration of various doses of ascorbic acid, 0 (control), 1.0, 1.5, 2.0, 3.0, and 5.0 g, on its concentration in aqueous humour, obtained from volunteer cataract patients was studied. RESULTS: The concentration of ascorbic acid in aqueous humour of control group (without administration of vitamin-C tablet or drug containing ascorbic acid was (254 +/- 119) mg.L-1. This study revealed that the administration of 2.0 g of ascorbic acid saturate the aqueous humour and further increase in the dose (3.0 g and 5.0 g) did not increase its concentration in aqueous humour, although its concentration was increased in plasma. CONCLUSION: Oral administration of 2.0 g of Vc is sufficient to saturate the aqueous humour where it may be helpful in controlling the intra-ocular pressure.     

Beta-carotene and protein oxidation: effects of ascorbic acid and alpha-tocopherol

The effect of beta-carotene on protein oxidation was examined under different oxygen (O(2)) tensions and with other antioxidants: alpha-tocopherol, ascorbic acid, and mixtures of antioxidants. Human serum albumin (HSA) was incubated with 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) to induce protein oxidation (carbonyl formation), under 15, 150, and 760 torr of O(2) tension. Antioxidant activity was related to O(2) tension, antioxidant concentrations and interaction between mixtures of antioxidants: (1) Under 15 torr of O(2), incubating HSA with AAPH, 1. 6 microM beta-carotene, 80 microM alpha-tocopherol, 160 microM ascorbic acid, and mixtures (0.1 microM beta-carotene, 5.0 microM alpha-tocopherol and 10 microM ascorbic acid) resulted in 24, 29, 39, and 44% reduction of carbonyl formation, respectively. (2) Under 150 torr of O(2) tension, the antioxidant effect of beta-carotene was decreased by 4% but increasing O(2) tension did not diminish the antioxidant effects of alpha-tocopherol, ascorbic acid, or antioxidant mixtures. (3). Under 760 torr of O(2) tension, adding 1. 6 microM beta-carotene resulted in 26% more carbonyl formation. (4) Under 760 torr of O(2) tension, the antioxidant effect of ascorbic acid was decreased 32% compared to what was observed at 150 torr of O(2) tension. Changes in O(2) tension had no effect on the antioxidant effect of alpha-tocopherol. The mixture of antioxidants inhibited carbonyl formation by 37% and was 7% less effective than that of 15 and 150 torr of O(2) tension. High concentration of beta-carotene produces more protein oxidation in the presence of high O(2) tension by a prooxidant mechanism. Mixtures of beta-carotene, alpha-tocopherol, and ascorbic acid provided better protective effects on protein oxidation than any single compound.     

Ex vivo cutaneous absorption assessmentof a stabilized ascorbic acid formulation using a microdialysis system

BACKGROUND: Reactive oxygen species generated by ultraviolet light result in photocarcinogenic and photoaging changes in the skin. Antioxidants protect the skin from these insults. OBJECTIVE: The aim of this study was to determine the ex vivo ascorbic acid penetration and its degradation in the skin after its topical application from an 8% new formulation. METHOD: Ascorbic acid was applied to human skin fragments. Ascorbic acid and its metabolites were collected by microdialysis and assessed by gas chromatography mass spectrometry. RESULTS: After topical application of the new formulation, the ascorbic acid level achieved was 8.5% higher than [corrected] times the normal tissue value. This high ascorbic acid dermal concentration remained constant if a topical application was made every 8 h. No degradation of ascorbic acid was detected. CONCLUSION: Ascorbic acid penetrates rapidly after its topical application. The persistent reservoir of ascorbic acid provides an important and attractive photoprotection strategy.     

Development and application of a novel UV method for the analysis of ascorbic acid

A UV method for the analysis of ascorbic acid with methanol as solvent to prepare a sample has been developed and applied. The effect of copper(II) concentrations on the oxidation of ascorbic acid in aqueous solution has been studied in detail, and the regularities of ascorbic acid oxidation in methanol, USP phosphate buffer (pH 2.50) and de-ionized water have been found. Upon experiments ascorbic acid has been found to dissolve in methanol, and its solubility in it has been measured to be 81.0 mg/ml at room temperature (22 °C). The ascorbic acid bulk material from a manufacturer has been assayed to be 89.34% with this method, in good agreement with the assay value (89.58%) from the titration method. The ascorbic acid granule and tablet content uniformity also has been tested using this method. This method is simple, rapid, accurate and reliable, and can be adopted for the routine determination of ascorbic acid in its granule and tablet formulations.     

Possible role of ascorbic acid in the oxidative damage induced by inhaled crystalline silica particles

The selective interaction of ascorbic acid with crystalline silica (quartz) has been studied by measuring the ascorbic acid consumption (by means of UV/vis and IR spectroscopy) and the release of silicon when quartz particles or amorphous silica (Aerosil 50) is incubated in ascorbic acid solution. At a physiological ascorbic acid concentration, quartz, and not amorphous silica, reacts, suggesting the formation of a 1:1 silicon-ascorbate complex, while at higher concentrations, the reacting amount of ascorbic acid exceeds the amount of silicon that is released. Silicon tetrahedra bearing free silanols at the quartz surface are selectively attached by ascorbic acid. The particle-derived hydroxyl radical yield in the presence of hydrogen peroxide is increased on ascorbic acid-treated quartz in comparison with the original sample. The results presented herein are relevant because the depletion of ascorbic acid from the lung lining layer and the increased potential in particle-derived free radical generation may both contribute to the oxidative damage following inhalation of crystalline silica.     

Behaviour of some organophosphorus and organochlorine pesticides in potatoes during soaking in different solutions.

The efficiencies of acidic solutions (radish, citric acid, ascorbic acid, acetic acid and hydrogen peroxide), neutral solutions (sodium chloride) and alkaline solution (sodium carbonate) as well as tap water in the elimination of organochlorine and organophosphorus pesticides from naturally contaminated potatoes were examined. The results indicated that acidic solutions were more effective than neutral and alkaline solutions in the elimination of the organochlorine compounds under investigation, Radish solutions eliminated pesticides completely, except o,p'-DDE (73.1% loss), followed by citric and ascorbic acid solutions. On the other hand, organophosphorus pesticides (pirimphos methyl, malathion and profenofos) were eliminated more by acidic, neutral and alkaline solutions than by organochlorines. The percentage of removal ranged from 98.5 to 100% for pirimphos methyl, 87.9 to 100% for malathion and 100% for profenofos.