Enzymatic assay with detection by enhanced luminol chemiluminescence in a reversed micellar system: determination of l-amino acids and glucose

A detection system for hydrogen peroxide, i.e., luminol chemiluminescence (CL) in a hexadecyltrimethylammonium bromide (CTAB) reversed micellar system, was coupled to enzyme reactions. The use of CTAB reversed micellar medium allows one to conduct both the oxidase enzymatic and CL detection reactions simultaneously at mild pH (l-amino acid system, pH 8.7; glucose system, pH 8.5) in the absence of any co-oxidant or catalyst. Based on this result, simple and unique determinations of l-amino acids and glucose as substrates were developed. The calibration graph for a representative amino acid, l-phenylalanine, was linear in the concentration range 4.0×10^?6?200×10^?6M with a relative standard deviation of 5.78% (five determinations). The method established for l-phenylalanine was also applicable for the assay of fourteen other l-amino acids. The calibration graph for glucose was linear in the concentration range 5.4×10^??540×10^?6M with a relative standard deviation of 4.27% (eight determinations). This method was compared with a standard spectrophotometric method (hexokinase) and successfully applied to the determination of glucose in human serum.     

Flow-injection chemiluminescence determination of ascorbic acid by use of the cerium(IV)-Rhodamine B system

A highly sensitive flow-injection (FI) method with chemiluminescence (CL) detection is used for the determination of l-ascorbic acid. The method is based on the CL reaction of Rhodamine B with cerium(IV) in sulfuric acid media. l-Ascorbic acid is suggested to be a catalyst utilized in the energy-transferred excitation process. The proposed procedure allows quantitation of l-ascorbic acid in the range 3.8×10⁻¹³ to 1.0×10⁻¹⁰ mol l⁻¹ with a correlation coefficient of 0.9998 (n=5) and relative standard deviation (R.S.D.) of 0.92% (n=11) at 1.0×10⁻¹¹ mol l⁻¹. The detection limit (3×blank) was 1.0×10⁻¹³ mol l⁻¹. The method is successfully used to determine l-ascorbic acid in fresh vegetables. The possible mechanism of the chemiluminescence in the system is discussed.     

Study on a Pyruvate Oxidase Biosensor Based on β-Cyclodextrin with Ferrocene as Electron-Transfer Mediator

Abstract

A pyruvic acid biosensor was constructed by the use of ferrocene, which was included in the β-cyclodextrin as electron-transfer mediator, as well as glutaraldehyde cross-linked membrane of egg white and β-cyclodextrin as matrix of enzyme immobilization. Because of the excellent electron-transfer efficiency of ferrocene, the microenvironment from β-cyclodextrin, and also the inclusion complexation between them, the biosensor has quite good properties. The linear detection limiting of this biosensor decreased to 5.68 × 10^?7 mol/L with excellent stability for 2.58% of relative standard deviation (RSD) during six individual detections.     

Wide linear range nanomaterial/ionophore-based electrode used for determination of lead in environmental and biological samples with differential pulse voltammetry

A new chemically modified carbon paste electrode is fabricated to determine lead ion concentration in its trace level in aqueous media with differential pulse voltammetry (DPV). The best performance is obtained by the carbon paste electrode composition including 20% of dithiodibezoic acid (DDA), 80% of high purity graphite powder and 60?µL of colloidal gold nanoparticle (AuNP) solution. The proposed electrode has a wide linear calibration response from 1?×?10^?9 to 6?×?10^?5 M with a detection limit of 6.6?×?10^?10?M, at pH 3.5. Seven replicate determination of 5?×?10^?8?M of lead ion concentration gives a relative standard deviation of 3.33%. The modified sensor is applied to determine lead contents in some environmental and biological Samples with satisfactory results.     

A Novel Voltammetric Method for the Determination of Maleic Acid Using Silver Amalgam Paste Electrode

An efficient voltammetric method was developed for the determination of maleic acid at a silver amalgam paste electrode (AgA‐PE) in Britton–Robinson buffer pH 2.0. The experimental parameters, such as pH of Britton–Robinson buffer, type of the supporting electrolyte and activation of the electrode surface were optimized. Under the optimal conditions, a linear response was observed over the 2×10^?6–1×10^?4 mol L^?1 maleic acid concentration range, determination limit being 5×10^?7 mol L^?1. A highly stable response, with a relative standard deviation (RSD) of 1.6% for 45 repetitive measurements of 1×10^?4 mol L^?1 maleic acid showed that there was no apparent surface passivation indicating the suitability of the method. The method was successfully applied for direct determination of maleic acid in drinking and river water.     

Plant tissue-based membrane biosensor for l-ascorbic acid

Coupling of a slice of the mesocarp of squash (Cucurbita pepo) or cucumber (Cucumis sativus) to a Clark-type oxygen electrode allows 0.02–0.57 mmol l^?1l-ascorbic acid to be determined amperometrically. The method is based on monitoring the decrease in the curretn of oxygen at an applied potential of ?650 mV vs. Ag/AgCl; oxygen is consumed in the analyte oxidation catalyzed by ascorbate oxidase in the plant tissue. One tissue slice serves for 50–80 measurements at 30°C and pH 6. Spare slices can be stored for at least a year in aqueous 50% glycerol without substantial loss of enzyme activity. The biosensor is highly selective towards ascorbic acid with a response time of 70–90 s, the relative standard deviation being about 3%. Satisfactory results were obtained in the analysis of some fruit juices and vitamin tablets.     

Flow—injection Chemiluminescence Sensor for the Determination of Gallic Acid by Immobilizing Luminol and Periodate on Anionexchange Resin

ＩｎｔｒｏｄｕｃｔｉｏｎＧａｌｌｉｃａｃｉｄｅｘｉｓｔｓｉｎｔｈｅｌｅａｖｅｓａｎｄｆｒｕｉｔｓｏｆｍａｎｙｔｙｐｅｓｏｆｐｌａｎｔｓａｎｄｉｓｗｉｄｅｌｙｕｓｅｄｉｎｍｅｄｉｃｉｎｅｆｏｒａｎｔｉ ｏｘｉ ｄａｔｉｏｎａｎｄａｎｔｉｂａｃｔｅｒｉａｌａｃｔｉｖｉｔｙ ,ａｎｔｉｆｌａｍｍａｔｏｒｙａｃｔｉｏｎａｎｄａｎｔｉ ｃａｎｃｅｒａｃｔｉｖｉｔｙ .1 5Ｉｎｓｐｉｔｅｏｆｔｈｅｈｅａｌｔｈｉｍｐｏｒｔａｎｃｅｏｆｇａｌｌｉｃａｃｉｄ ,ｉｔｓｍｅｔａｂｏｌｉｓｍａｎｄｋｉｎｅｔｉｃｓｉｎｔｈｅｈｕ…     

Sequential extraction partitioning of metals,sulfur, and phosphorus in bottom ash from a coal-fired power plant

Abstract

The herbicide trifluralin was analysed by adsorptive stripping voltammetry on a glassy carbon electrode. The linear concentration range was 2.5 × 10^?7 M – 1.25 × 10^?6M when using 5-min preconcentration at open circuit conditions in Britton-Robinson buffer of pH 7.0. The detection limit of trifluralin was 2.5 × 10^?8M. The relative standard deviation was 3.3% at a concentration of 1.0 × 10^?6M (n=5). The method was applied to the determination of trifluralin in soil with good recovery.     

Determination of Cd(II) in Some Foodstuffs by Anodic Stripping Pulse Voltammetry (ASPV) using Glassy Carbon Electrode

Abstract

Cadmium in the presence of 0.04 M NaCl as the electrolyte was determined using stripping voltammetry with superimposed constant amplitude pulses of negative polarity (SVPNP) or positive polarity (SVPPP), and differential pulses stripping voltammetry using rotating disc glass carbon electrode (RDGCE). The SVPNP was found to give the greatest sensitivity. The anodic peak was obtained at potential ?850 to ?795 mV due to the oxidation of cadmium to cadmium(II). Linear calibration curves were obtained in the concentration range between 1.5×10^?9–2×10^?10 M. The relative standard deviation is 4.25% at very low concentration of 2×10^?10 M. This method was successfully applied to the determination of cadmium in some foodstuffs (wheat and its products, vegetables) after acid digestion.     

Direct Determination of Labile Monomeric Aluminum in Natural Waters By A.C. Oscillopolarography in the Presence of Rubeanic Acid

ABSTRACT

A simple and sensitive electrochemical method for the direct determination of labile (monomeric inorganic Al speciation) Al concentration in natural waters is developed in this paper. It is based on the use of a.c. oscillopolarography in the presence of rubeanic acid (RA). The optimal experimental conditions are: 1 mol/L NaAc-HAc buffer (pH 5.4) and a RA concentration of 6x10^?4 mol/L. The response is linear over the 2x10^?7 to 2x10^?6 mol/L concentration range. The detection limit is 1x10^?7 mol/L and the relative standard deviation (at the 1.2 x 10^?6 mol/L level) is 5.5%. The method has been applied to the direct determination of labile monomeric Al concentrations in various natural samples. The results were verified by the classic ion exchange method.     

Spectrophotometric Determination of Nitrite in Aqueous Solution by the Diazotization-Coupling Method with Orthanilic Acid-Resorcinol

Abstract

A spectrophotometric method for the determination of nitrite is described. It relies upon the reaction of this ion with an acidified orthanilic acid solution to form a diazonium ion, which is subsequently coupled with resorcinol, in alkaline medium, to form immediately a yellow-colored stable water-soluble and intense azo dye having maximum absorption at 426 nm. The linear absorbance plot with concentration indicates that Beer's law is obeyed over the range of 1-12 μg of nitrite in a final volume of 10ml, with a molar absorptivity of 38.7 × 10³1 mol^?1cm^?1, sensitivity index of 0.0012μgcm^?3, relative error of –0.5 to +0.2% and relative standard deviation of 0.43-3.5%, depending on the concentration level. The optimum conditions affecting and related to the color reaction and interference due to foreign ions have been studied.     

Determination of acetaldehyde by a chemiluminescence method

The determination of acetaldehyde was achieved by monitoring the chemiluminescence emission from the luminol-potassium hexacyanoferrate (III) reaction in the presence of xanthine oxidase. The linear range was three orders of magnitude, the detection limit (2σ) was 4 × 10^?7 M and the relative standard deviation (n = 5) was 10.6% for 4.3 × 10^?7 M. No interference was observed from seven organic and inorganic species at a 1000-fold excess relative to a concentration of 1 × 10^?5 M acetaldehyde.     

Spectrophotometric determination of micro amounts of cationic polymeric flocculants by flow injection analysis

Cationic polymeric flocculants in water are determined spectrophotometrically with the anionic compound 3-(2-hydroxy-3-carboxyanilide-1-azonaphthalene)-4-hydroxybenzenesulfonic acid at pH 10 by flow injection analysis. The calibration graph at 680 nm is rectilinear from 0 to 20 mg l^?1 under optimal conditions. The relative standard deviation for 20 injections of Cat-Floc (10 mg l^?1) was 1.2%; the sample throughput was 60 h^?1.     

Rapid Method for the Micro-Determination of Hydrazine by Amperometric Titration With Potassium Iodate

Abstract

An amperometric method, with potassium iodate as the titrant, for the rapid and precise determination of micro amounts of hydrazine salts is described. Hydrazine dihydrochloride, hydrazine sulfate and hydrazine hydrate could be quantitatively analyzed at the concentration range of 4 × 10^?7 -4×10^?3 M in the presence of 5 M hydrochloric acid. Hydrazine salts, 2×10^?4 -4×10^?3 M, were titrated in 5 minutes with a relative error and a relative standard deviation of 0.1%. It was also found that hydrazine dihydrochloride can be precisely determined, without any interference, even in the presence of hydroxylamine which is ten times as much as the former.

The suitable applied potential between the rotating platinum indicator microelectrode and the silver plate-silver chloride reference electrode was + 0.7V.     

Determination of Folic Acid by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of folic acid at an in situ plated lead film electrode was described. Formation of lead film on a glassy carbon substrate and accumulation of folic acid was performed simultaneously from an acetate buffer solution of pH 5.6 at the potential ?0.88 V. The measurements were carried out from aerated solutions. The calibration graph for an accumulation time of 300 s was linear from 2×10^?9 to 5×10^?8 mol L^?1. The detection limit was 7×10^?10 mol L^?1, the relative standard deviation for 2×10^?8 mol L^?1 of folic acid was 3.9%. The proposed procedure was applied to folic acid determinations in pharmaceutical preparations.     

Application of ion-selective electrodes in environmental analysis : Determination of Acid and Fluoride concentrations in Rain-water with a Flow-Injection System

A flow-injection method is described for the measurement of acid and fluoride concentrations. The conditions were optimized to ensure small sample and reagent consumption, low detection limit and the highest rate of analysis allowed by the potentiometric sensor. With a microcapillary pH-sensitive glass electrode, 20-μl sample volumes and 1.0–1.5 ml min^?1 carrier flow rates, strong acids were determined at concentrations as low as 10^?5 M (0.2 nmol of acid in 20 μ1). The relative standard deviation was about 1% at 10?4 M strong acid concentration at an injection rate of 500–550 h^?1. With a flow- through fluoride-selective electrode, 250-μl sample volumes and a 1 ml min^?1 carrier flow rates, fluoride concentrations as low as 10^?7 M were measured (ca. 0.5 ng of fluoride in 250 μ1). The injection rate was 40 h^?1 at concentrations below 10^?6 M, but 60 h^?1 above 10^?5 M. The methods were used successfully for determining the acid and fluoride concentrations in rain-waters.     

Flow injection spectrophotometric determination of ascorbic acid in soft drinks and beer

Two spectrophotometric methods, a photochemical and a non-photochemical, for the determination of ascorbic acid in soft drinks and beer using a flow-injection system are proposed. The non-photochemical method is based on the redox reaction that takes place between ascorbic acid and Fe(III), yielding dehydroascorbic acid and Fe(II). Fe(II) reacts with 1,10-phenantroline, originating the reddish orange Fe(phen)₃ ²⁺ complex (ferroin). This complex is spectrophotometrically monitored at 512 nm, and the signal is directly related to the concentration of ascorbic acid in the sample. The photochemical method has the same basis, nevertheless, uses the irradiation with visible light to enhance the redox reaction and so achieve higher sensitivities in the analysis. The non-photochemical method shows a linear range between 5 and 80 μg mL^?1, with a relative standard deviation of 1.6% (n = 11), a detection limit of 2.7 μg mL^?1 and a sample throughput of ¶60 samples h^?1. The photochemical method shows a linear range between 1 and 80 μg mL^?1, with a relative standard deviation of 1.0% (n = 11), a detection limit of 0.5 μg mL^?1 and a sample throughput of 40 samples h^?1.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Fluorimetric determination of nitrate in natural waters with 3-amino-1,5-naphthalenedisulphonic acid in a flow-injection system

A rapid, sensitive and precise flow-injection method for the determination of nitrate in natural waters is presented. Nitrate is first reduced in a copperized cadmium column to nitrite, which reacts with 3-amino-1,5-naphthalenedisulphonic acid to form the azoic acid. This acid forms a fluorescent salt in alkaline medium. The injecton rate is about 30 h^?1, the relative standard deviation for 10 injections of 2 × 10^?5 M nitrate is 0.8%, and the detection limit (S/N = 3)_is 1 × 10^?8 M nitrate.     

Determination of Gallic Acid by Flow Injection with Electrochemiluminescent Detection

ABSTRACT

Potential dependent inhibition and enhancement effects of gallic acid on the electrochemiluminescence (ECL) of luminol in alkaline solutions were found. On the basis of the enhancement effect, a flow injection method was developed for the determination of gallic acid. The method was simple, convenient and sensitive. A detection limit of 1.8×10^?8 mol/L, linear range of 3.0×10^?8 - 1.0×10^?4 mol/L, relative standard deviation of 1.0% for eleven measurements of 5.0×10^?6 mol/L of gallic acid was found. This method was successfully applied to determine the content of gallic acid in Chinese gall (moshizi).