Flow-injection determination of malate with immobilized malate dehydrogenase

Malate dehydrogenase (MDH) is immobilized chemically on controlled-pore glass and used on-line in a glass minicolumn (25×2.5 mm i.d.). Malate solution passes through the minicolumn of immobilized MDH and the NADH formed is monitored spectrophotometrically from 9 × 10-^?4 down to 7 × 10^?6 M (36 ng in 40 μl) at 50 samples h^?1.     

Comparative study of potentiometric and amperometric tissue-based electrodes for oxalate

Acetone-precipitated pulp from banana skins is physicall entrapped at the tip of a carbon dioxide gas-sensor and on a hydrogen peroxide sensor probe to determine oxalate potentiometrically and amperometrically in aqueous solution and inurine. The enzyme present in the tissue is oxalate oxidase. The potentiometric response has a slope of 47–50 mV/decade for 1 × 10^?4 M–2 × 10^?3 M oxalate with a detection limit of 2 × 10^?5 M. The amperometric response is linear for 2 × 10^t-5–3 × 10^?4 M oxalate with a dectection limit of 2 × 10^?6 M. Average recoveries of oxalate added to aqueous samples were 96.2% and 98.0%, and average relative standrd deviations were 3.8% and 3.6% for the potentiometric and amperometric systems, respectively. Oxalate was determined in six control urine samples, with relative errors of about 2.5%, by both electrode systems after a simple clean-up.     

Flow-injection determination of l-tyrosine in serum with an immobilized tyrosinase reactor and fluorescence detection

Tyrosinase is immobilized on controlled-pore glass beads and packed into a stainless-steel column (5 cm × 4 mm i.d.). Serum is deproteinized with tungstate and sulphuric acid. The carrier stream is 0.3 M phosphate buffer (pH 7.2), and is mixed with 5 M potassium hydroxide after the enzyme reactor. The fluorescent dihydroxyindole formed is detected at 490 nm (excitation at 375 nm). The calibration graph is linear for 1 × 10^?7 ?1 × 10^?4 M tyrosine; the detection limit is 2 × 10^?8 M.     

Flow-injection determination of sulphite and assay of sulphite oxidase

Sulphite (1–80 × 10^?5 M) in formaldehyde-stabilized solutions is determined by injection into a flowing stream of pH 8.5 phosphate buffer, passing through a mini-column of sulphite oxidase immobilized on controlled-pore glass, with amperometric detection of the hydrogen peroxide produced. Sulphite oxidase (5–100 U l^?) is determined by injection into a flowing stream of formaldehyde-stabilized 2 × 10^?3 M sodium sulphite in pH 8.0 phosphate buffer; hydrogen peroxide is again monitored.     

Spectrophotometric determination of copper by flow injection analysis with an on-line reduction column

A silver reductor minicolumn is used ina flow-injection system for reduction of copper(II) to copper(I), which is detected spectrophotometrically using bathocuproine disulphonic acid. The reductor functions very well at flow rates up to 4 ml min^?1; this allows sample injection ar rates up to 120 h^?1. Linear calibration is achieved for 5 × 10^?7– 1 × 10^?4 M copper. The detection limit is 3.4 ng and the midrange precision is 1%.     

Determination of glucose in blood by flow injection analysis and an immobilized glucose oxidase column

A flow-injection system for glucose determination is described. Glucose oxidase is immobilized on controlled porosity glass (CPG) and used in a glass column (2.5 mm diameter × 2.5 cm). The hydrogen peroxide produced by the enzymatic reaction (? 1 × 10^?6 M) is detected by the current produced in a flow-through cell, with two platinum electrodes having a potential difference of 0.6 V. Glucose (0–20 mmol l^?1) can be determined in blood plasma either with a dialyser in the system or, better, by incorporating a column of copper(II) diethyldithiocarbamate on CPG before the enzyme column. The results compared well with those obtained by a conventional analyser system. The glucose oxidase column showed little change in activity over a 10-month period.     

Flow-injection spectrophotometric determination of acetyl-coenzyme A with immobilized phosphotransacetylase

Phosphotransacetylase (PTA) is immobilized on AF-Tresyl TOYOPEARL 650 gel and used on-line in a stainless-steel column (10 × 4 mm i.d.). CoA-SH liberated enzymatically from acetyl-CoA is reacted with Ellman's reagent [5,5′-dithiobis(2-nitrobenzoic acid)] in the carrier stream. The calibration graph for acetyl-CoA is linear from 4 × 10^?6 to 4 × 10^?4 M and the detection limits is 8 × 10^?7 M. The immobilized enzyme can be employed for over 4 months without any significant decrease in activity. The enzyme retains its activity in methanol even though the initial rate of reaction is decreased.     

Cyclic regeneration of nicotinamide adenine dinucleotide with immobilized enzymes: Flow-injection spectrofluorimetric determination of ethanol

Ethanol (0.05–0.5%) in water is determined by injection of a 20-μl sample into a solution of 1.5 × 10^?3 M NAD⁺ in pH 8.0 phosphate buffer flowing from a reservoir. The solution passes through a minicolumn of yeast alcohol dehydrogenase immobilized on controlled-pore glass (CPG). The NADH formed is monitored spectrofluorimetrically in the flow system, before reconversion to NAD⁺ in a minicolumn of glutamate dehydrogenase immobilized on CPG in the presence of glutarate and ammonium ions, also in the flowing solution. The solution then returns to the reservoir. The regeneration of NAD⁺ allows the same coenzyme solution to be used for 50 ethanol determinations daily for 4 days.     

Enzymatic methods for the determination of ethanol based on linear and cyclif flow-injection systems

Linear and cyclic systems are described for the determination of ethanol (ca. 0.17–30×10^?3 M). In the linear system, the solution passes either through a minicolumn of yeast alcohol dehydrogenase (YADH) immobilized on controlled-pore glass or through minicolumns of the immobilized YADH and of yeast aldehyde dehydrogenase immobilized on cyanogen bromide-activated Sepharose-4B. The NADH formed is monitored either spectrophotometrically or spectrofluorimetrically. In the cyclic system, the solution passes through the same enzyme columns, and the NADH produced is monitored similarly before reconversion to NAD⁺ in a minicolumn of glutamate dehydrogenase immobilized on cyanogen bromie-activated Sepharose-4B in the presence of α-ketoglutarate and ammonium ions also present in the flow system. the sample throughout for both systems is ca. 40 h^?1 and 50 h^?1 for spectrophotometric and spectrofluorimetric detection, respectively. An on-line double-injection technique is described as an alternative to the cyclic system for limiting the consumption of NAD⁺.     

Determination of pesticides in vegetable samples using an acetylcholinesterase biosensor based on nanoparticles ZrO2/chitosan composite film

An amperometric pesticides inhibition biosensor has been developed and used for determination of pesticides in vegetable samples. To eliminate the interference of ascorbic acid, multilayer films of polyelectrolyte (chitosan/polystyrensulfonate) were coated on the glass carbon electrode. Then, acetylcholinesterase was immobilized on the electrode based on surface-treated nanoporous ZrO₂/chitosan composite film as immobilization matrix. As a modified substrate, acetylthiocholine was hydrolysed by acetylcholinesterase and produced thiocholine which can be oxidized at +700?mV vs. SCE. Pesticides inhibit the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to acetylthiocholine within 9.90?×?10^?6 to 2.03?×?10^?3?M. The electrode provided a linear response over a concentration range of 6.6?×?10^?6 to 4.4?×?10^?4?M for phoxim with a detection limit of 1.3?×?10^?6?M, over a range of 1.0?×?10^?8 to 5.9?×?10^?7?M for malathion, and over a range of 8.6?×?10^?6 to 5.2?×?10^?4?M for dimethoate. This biosensor has been used to determine pesticides in a real vegetable sample.     

Determination of uranium using a flow system with reagent injection. Application to the determination of uranium in ore leachates

The determination of uranium by a flow system with reagent injection is based on the reaction of U(IV) with Arsenazo III in 3.6 M HCl; U(IV) is generated by reduction of uranyl ion in a lead reductor minicolumn installed in the sample channel of the manifold. The interference effect caused by several ions is studied. The calibration graph is linear up to 1.0 × 10^?5 M (2.4 mg l^?1) and the detection limit is 2.8 × 10^?8 M (6.6 μg l^?1). The modification of the manifold by including a second valve to by-pass the reducing column allows the measurement of the difference in peak heights, which makes the method specific for uranium.     

Indirect Differential Pulse Voltammetric Determination of Aluminum Biological Samples in the Presence of 3, 4-Dihydroxyphenylalanine

ABSTRACT

Indirect differential pulse voltammetric (DPV) determination of aluminum in the presence of 3, 4-dihydroxyphenylalanine (L-dopa) with glass carbon electrode as working electrode has been described. The method relies on the decrease of DPV anodic peak current of L-dopa with the addition of Al^III The decreasing value of the peak current is linear with the increase of Al^III concentration. Under the optimum experimental conditions (pH 4.8, 6×10^?4 M L-dopa, 0.06M NaAc - HAc ¹buffer solution), the linear ranges are 4.0×10^?7 - 5.2×10^?6 M and 7.2×10^?6 - 4.5×10^?5 M. The relative standard deviation for 8×10^?6 M aluminum is 1.0% (n = 8) and the detection limit is 3.5×10^?7 M. A number of foreign species for interference have been studied. The method has been applied to determine aluminum in drinking water, synthetic renal dialysate and urine samples.     

Determination of the pesticides fenthion and fenitrothion by flow injection with amperometric detection

The response of a glassy carbon amperometric detector in a flow system was studied. The values of the hydrodynamic variables were optimized. The detector functioned as a “thin-layer” cell. Methods are proposed for the determination of 1.6 × 10^?7?1.6 × 10^?5 Fenthion and 8 × 10^?6? 8× 10^?5 M Fenitrothion in a methanolic acetate-buffered carrier stream. The detection limits were 0.15 and 0.52 μM, respectively.     

Chemiluminescence Sensor with Mn(III)-Tetrakis (4-sulfonatophenyl)-porphyrin Immobilized on Dioctadecyldimethylammonium Chloride Bilayer Membranes Incorporated Into PVC Film

Abstract

An indicator phase for a flow-through chemiluminescence (CL) sensor composed of ordered surfactant assemblies, a polymer and a catalyst was evaluated by measuring adrenaline. The method is based on use of Mn (III)-porphyrin immobilized on a bilayer membrane contained in a blended film, prepared by incorporating dioctadecyl-dimethylammonium chloride into polyvinyl chloride. The sensor consisted of a Pyrex glass tube (30 mm × 5 mm i.d.) packed with silica glass wool, on which the indicator phase was coated, and a photomultiplier tube. The blend film functioned as a favorable reaction medium for the adrenaline CL, and further enhanced CL was observed with the immobilized catalyst. This indicator phase permitted adrenaline to be detected down to 3 × 10^?6 M with a 20 μl injection into a 0.3 M NaOH carrier solution. The relative standard deviation (n = 10) was 1.0% for 5 × 10^?5 M adrenaline. For 80 successive injections of 5 × 10^?5 M adrenaline, the variation of the CL signal was within the relative standard deviation. Almost the same sensitivity and precision were observed with the indicator phase stored in water for at least 3 days. The sensor was successfully applied to determine adrenaline in drug samples.     

Spectrophotometric determination of iodate,iodide and acids by flow injection analysis

The production of iodine by reaction of iodate and iodide in acidic solution is used for the spectrophotometric determination of 1–6 × 10^?5 M iodate, 2–8 × 10^?3 M iodide, and ca. 10^?3 M acids. The sample is injected into a carrier stream containing the other two ions. The injection rate is ca. 100 h^?1.     

Effect of metal ions on a piezoelectric quartz crystal in aqueous solution and the adsorptive determination of iron(III) as phosphate

At 1.5 V applied between the electrodes on the piezoelectric crystal, many metals electrodeposit on an electrode so that the frequency changes. Iron(III) (1 × 10^?5-1 × 10^?4 M) can be determined by adsorption of iron(III) phosphate which also causes a frequency change. Electrodeposition can be prevented by covering one electrode with a thin glass plate.     

Flow-Injection Spectrophotometric Determination of Oxalate,Citrate and Tartrate Based on Photochemical Reactions

Abstract

A flow-injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochemical decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochemical reactions was detected by measuring the absorbance after complexation with ferrozine (λ_max=562 nm). Linear calibration graphs were obtained over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?4 M, 8 × 10^?6 - 1.8 × 10^?4 M and 1.0 × 10^?6 - 2 × 10^?5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1x10^?5 M concentration level were within the range 1.29 - 1.47 %. The sampling frequency was about 40 samples h^?1. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.     

A solid-state chemiluminescence detector for hydrogen peroxide based on an immobilized luminophore : Application to Rain Water

The construction and functioning of a chemiluminescence detector for hydrogen peroxide is described. It is based on peroxyoxalate chemiluminescence and consists of a two-bed reactor packed with solid trichlorophenyloxalate (TCPO) and 3-aminofluoranthene immobilized on controlled pore glass beads. Optimal conditions (pH, solvent, TCPO purity) for flow-independent operation are discussed. Samples can be injected into a moving stream or directly into the monitor with a syringe so as to provide a manually operated field monitor. The detection limit is 1.5 × 10^?8 M, and calibration graphs are linear over six orders of magnitude. The r.s.d. for the manual monitoring mode is ±3% for 17 μg l^?1 hydrogen peroxide. A sample throughput of 100 h^?1 is possible in the flow injection mode, and 40 samples h^?1 for manual injection.     

A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10^?6?2 × 10^?4 M could be determined with an accuracy of ± 10^?6 M. For CTABr, these numbers were 3 × 10^?6?2 × 10^?4 M and ± 5 × 10^?7 M; for BACl, they were 2 × 10^?3?9 × 10^?2 g l^?1 and ± 1 × 10^?3 g l^?1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10^?6 M and × 1 × 10^?3 g l^?1, respectively.     

Spectrophotometric and spectrofluorimetric determination of iodide by extraction of ICl−2 with rhodamine B

Iodide is determined after oxidation with nitrous acid in 5 M hydrochloric acid to ICl^?₂. The ion-pair formed with rhodamine B is extracted into toluene and measured spectrophotometrically (0.5–5 × 10^?5 M) or spectrofluorimetrically (1–10 × 10^?6 M). The relative standard deviations were 1.8% for the determination of 5 × 10^?6 M iodide (n = 5) by spectrofluorimetry and 2.3% (n = 50) for 1 × 10^?5 M iodide by spectrophotometry. Periodate, iodate and iodine responded exactly as iodide.