Flow-injection amperometric determination of oxalate with immobilized oxalate oxidase

Oxalate is immobilized on controlled-pore glass and is used on-line in a glass minicolumn (2.5×25 mm). The hydrogen peroxide formed is detected amperometrically. Oxalate (6×10^?6?9×10^?4 M) is determined in a flowing stream of pH 3.5 citrate (or succinate) buffer. As little as 20 ng (in 40 μl; 5.7×10^?6 M) of oxalate can be detected. Copper inhibition can be removed either by adding EDTA to the carrier stream or incorporating a chelating-resin minicolumn into the flow system prior to the enzyme column.     

Flow-injection amperometric determination of chlorine at a gold electrode

The applied potential is +0.2 V vs. SCE, flow rate is 1 ml min^?1 and sample volume is 30 μ1. The background electrolyte is 0.05 M phosphate, pH 7.4. Electrode pretreatment is +1.3 V vs. SCE for 40 s, followed by a pre-injection delay of 20 s. Peak current over a receding baseline is used. Linear range extends down to 0.4 μM for chloramine and 0.2 μM for hypochlorite. Sensitivities are 70 and 95 nA μM^? respectively. Time per determination is less than 1.5 min. Monochlorinated glycine is active whereas chlorinated cyanuratesshow no response. Chlorine and monochloramine in river water were determined.     

Flow-injection determination of nitrites based on their reaction with thiocyanates

A technique for the flow-injection determination of nitrites with spectrophotometric signal detection was developed and studied. Additionally, a combination of the developed technique with the on-line pre-concentration of low concentrations of nitrites in surface and potable waters was investigated. The technique is based on the reaction of nitrites with thiocyanates. The product of the analytical reaction (nitroso-S-thiocyanate) and its adducts with strong acids are stable in aqueous solutions, which is supported by quantum chemical calculations. It is shown that the reaction chosen is attractive for analytical applications, because it is highly selective. A decrease in the detection limit down to 1.5 ng/mL (3s) is achieved by combining FIA with on-line ion-exchange preconcentration. The technique developed is used for monitoring nitrites in natural and waste water. The throughput capacity is 300 samples per hour.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 323–330.Original Russian Text Copyright © 2005 by Kuznetsov, Zemyatova, Ermolenko.     

Flow-injection analysis with the iron-induced perbromate-iodide reaction: spectrophotometric determination of iron

Total iron is determined by a flow-injection spectrophotometric technique. The production of I(-)(3) from the iron(II)- or iron(III)-induced perbromate-iodide reaction is monitored at 353 nm. Calibration graphs are linear from 10 to 100 ng/ml with correlations up to 0.9998 and can be extended up to 10 microg/ml by appropriate adjustment of conditions. The average sampling rate is 30 samples/hr. Detection limits and relative standard deviations compare well with those of other FIA methods.     

Flow-injection determination of starch and total carbohydrate with an immobilized glucoamylase reactor and pulsed amperometric detection

Starch and total carbohydrate are determined by using a flow-injection system comprised of an immobilized glucoamylase reactor followed by pulsed amperometric detection of the glucose produced. Glucoamylase, immobilized onto porous silica and packed into a short stainless steel column, is capable of nearly quantitative (98%) conversion of the starch to glucose. The sensitivity of pulsed amperoemtric detection for soluble starch is increased 26-fold by first passing the starch through the immobilized glucoamylase reactor. This system is successfully used to determine total carbohydrate in beer samples. The method is simple, rapid and sensitive for starch.     

Flow-injection determination of some sulphur anions via the catalyzed iodine-azide reaction

Investigations of the catalysis by sulphide, thiosulphate and thiourea of the iodineazide reaction under flow-injection conditions showed that the reaction was complete within 15 s, 30 s and 2 min, respectively. Determination of 0–1.0×10^?3 M sulphide, 0–8.0×10^?4 M thiosulphate and 0–1.0×10^?3 M thiourea is possible under optimized flow conditions. Catalysis by thiocyanate did not occur under these conditions so that thiosulphate could be determined in the presence of thiocyanate.     

Flow-injection spectrophotometric determination of ascorbic acid in pharmaceutical products with the Prussian Blue reaction

A lot of modern analytical strategies for exploiting chemistries have been developed by using flow-injection analysis. However, even after 20 years of flow-injection evolution, there still are new quantitative procedures being established using old qualitative assays. The formation of Prussian Blue is a classical test to detect Fe(2+) using hexacyanoferrate(III) as a precipitating reagent. This reaction was evaluated for spectrophotometric determination of ascorbic acid employing Fe(3+) and hexacyanoferrate(III) as chromogenic reagents. An excess of the complexing anion avoids the formation of precipitate and forms a deep blue solution when Fe(3+) is reduced to Fe(2+) by ascorbic acid. The maximum absorbance of the colored complex occurs at 700 nm and the molar absorptivity is 3.0 x 10(4) 1 mol(-1) cm(-1). Under flow-injection conditions the Prussian Blue reaction was employed with an intermittent flow of an oxalate alkaline solution for removing the colored product adsorbed on tube and flow-cell walls. Reference solutions containing 5.0 x 10(-6)-1.0 x 10(-4) M of ascorbic acid were employed to obtain the analytical curve (r = 0.9999). For all solutions the relative standard deviation was lower than 1.0% (n=10). Results obtained for ascorbic acid determination in pharmaceutical products (Cewin, Redoxon and Cebion) are in good agreement with those obtained by using a flow-injection procedure involving the reaction between triiodide and ascorbic acid. The sampling frequency is 140 h(-1) and only 430 microl of reagents is consumed in each determination.     

Flow-injection determination of acetone with diazotized anthranilic acid through a fluorescent reaction intermediate

Acetone and diazotized anthranilic acid react in alkaline solution, giving a fluorescent intermediate that can be measured at excitation and emission wavelengths of 305 and 395 nm, respectively. Based on this, a fluorimetric flow-injection method is proposed for the determination of acetone in aqueous solution. Under the proposed conditions, acetone can be detected at concentrations higher than 8 × 10⁻⁷ M, with a linear application range from 1 × 10⁻⁶ to 2 × 10⁻⁴ M and an R.S.D. of 2.7% (1.0 × 10⁻⁵ M, n = 10). A sampling frequency of 24 h⁻¹ is achieved. Some potentially interfering species are investigated.     

Flow-injection amperometric determination of pesticides on the basis of their inhibition of immobilized acetylcholinesterases of different origin

Determination of the organophosphorus pesticides paraoxon, chlorpyrifos oxon, and malaoxon has been performed by a method based on inhibition of acetylcholinesterase (AChE) and amperometric detection in a flow-injection system with enzymes obtained from the electric eel (eeAChE) and Drosophila melanogaster (dmAChE) and immobilized on the surface of platinum electrode within a layer of poly(vinyl alcohol) bearing styrylpyridinium groups. dmAChE is more sensitive than eeAChE to inhibition by chlorpyrifos oxon and paraoxon. The sensitivity difference was largest for chlorpyrifos oxon (detection limit approx. 17 times lower), and practically none for malaoxon. Determination of the analytes in spiked river water samples by use of the dmAChE biosensor resulted in recoveries from 50 to 90 % for chlorpyrifos oxon at levels of 20 to 40 nmol L(-1), 50 to 100 % for paraoxon at 0.6 to 0.8 micro mol L(-1), and 140 to 190 % for malaoxon at 0.6 to 1.2 micro mol L(-1).     

Differential amperometric determination of hydrogen peroxide in honeys using flow-injection analysis with enzymatic reactor

Hydrogen peroxide (H2O2) present in honey was rapidly determined by the differential amperometric method in association with flow-injection analysis (FIA) and a tubular reactor containing immobilized enzymes. A gold electrode modified by electrochemical deposition of platinum was employed as working electrode. Hydrogen peroxide was quantified in 14 samples of Brazilian commercial honeys using amperometric differential measurements at +0.60V vs. Ag/AgCl((sat)). For the enzymatic consumption of H2O2, a tubular reactor containing immobilized peroxidase was constructed using an immobilization of enzymes on Amberlite IRA-743 resin. The linear dynamic range in H2O2 extends from 1 to 100 x 10(-6) mol L(-1), at pH 7.0. At flow rate of 2.0 mL min(-1) and injecting 150 microL sample volumes, the sampling frequency of the 90 determinations per hour is afforded. This method is based on three steps involving the flow-injection of: (1) the sample spiked with a standard solution, (2) the pure sample and (3) the enzymatically treated sample with peroxidase immobilized. The reproducibility of the current peaks for hydrogen peroxide in 10(-5) mol L(-1) range concentration showed a relative standard deviation (R.S.D.) better than 1%. The detection limit of this method is 2.9 x 10(-7) mol L(-1). The honey samples analyses were compared with the parallel spectrophotometric determination, and showed an excellent correlation between the methods.     

Flow-injection analysis-spectrophotometric determination of nitrite and nitrate in water samples by reaction with proflavin

A flow-injection manifold is proposed for determination of nitrite based on the reaction with 3,6-diamino acridine (proflavin sulfate) in hydrochloride acid medium. The assembly is adapted for nitrate determination by including a reductive column filled with copperized cadmium. The influence of foreign substances is also studied. The method gives a linear calibration graph over the range 0.06-4 mg 1(-1) nitrite, with an RSD <0.5%. The method was applied to nitrite and nitrate determinations in either waste water or coastal marine water samples.     

Flow-injection determination of meptazinol with electrochemical detection

A flow-injection analysis system incorporating a glassy carbon voltammetric detector cell is described. Meptazinol (0.01–10 μg ml^-1) can be determined by electro-chemical oxidation in a carrier stream of 0.05 M sodium acetate—0.1 M acetic acid in 98% ethanol at sampling rates up to 80 samples per hour.     

Flow-injection extraction-spectrophotometric determination of permanganate with the triphenylsulphonium cation

Summary Permanganate can be determined spectrophotometrically at 548 nm after flow-injection extraction into chloroform of the ion-associate triphenylsulphonium permanganate. The carrier stream was a pH 6 buffer containing 10% (w/v) ammonium fluoride and the reagent stream was 0.10% (w/v) triphenylsulphonium chloride. The injection rate was 20 h^–1. The calibration graph is linear up to 40 g ml^–1 and the detection limit is 1.10 g ml^–1 Mn(VII), based on injection volumes of 250 l. The system has been applied to the determination of manganese in steels and a cupro-nickel alloy.     

Flow-injection chemiluminescence determination of aminomethylbenzoic acid and aminophylline based on N-bromosuccinimide-luminol reaction

A novel and sensitive chemiluminescence (CL) method for the determination of aminomethylbenzoic acid and aminophylline coupled with flow-injection analysis (FIA) technique is developed in this paper. It is based on the inhibition effect of the studied drugs on the chemiluminescence emission of N-bromosuccinimide-luminol (NBS-luminol) system. Under the optimum conditions, the decreased CL intensity is linear with the concentration of aminomethylbenzoic acid in the range of 2×10⁻⁸ to 1.0×10⁻⁶ g ml⁻¹ and with the concentration of aminophylline in the range of 1×10⁻⁷ to 7.0×10⁻⁶ g ml⁻¹, respectively. The detection limit is 7.0×10⁻⁹ g ml⁻¹ for aminomethylbenzoic acid (3σ) and 3.4×10⁻⁸ g ml⁻¹ for aminophylline (3σ). The relative standard deviations (R.S.D.) for 11 parallel measurements of 2.0×10⁻⁷ g ml⁻¹ aminomethylbenzoic acid and 1.0×10⁻⁶ g ml⁻¹ aminophylline are 2.6 and 3.0%, respectively. The proposed methods have been applied for the determination of the studied drugs in their pharmaceutical formulations with satisfactory results. The possible use of the proposed system for the determination of aminomethylbenzoic acid in plasma sample was also tested. The possible inhibition mechanism of aminomethylbenzoic acid and aminophylline on luminol-NBS system was discussed briefly.     

鲁米诺-溴酸钾体系增敏化学发光法测定抗坏血酸

基于碱性条件下抗坏血酸对KBrO3-鲁米诺化学发光体系的增敏作用,结合流动注射技术建立了一种测定抗坏血酸的新方法,抗坏血酸测定的线性范围为1.0×10-8～3.0×10-7mol/L,线性相关系数为0.9981(n=7),检出限为7.0×10-9mol/L,对7.0×10-8mol/L的抗坏血酸进行了平行测定(n=11),其相对标准偏差为1.5%。方法可用于水果、VC药片和VC针剂中抗坏血酸的测定。     

Flow-injection determination of total organic fluorine with off-line defluorination reaction on a solid sorbent bed

Considering recent reports on widespread occurrence and concerns about perfluoroalkyl substances (PFAS) in environmental and biological systems, analysis of these compounds have gained much attention in recent years. Majority of analyte-specific methods are based on a LC/MS/MS or a GC/MS detection, however many environmental or biological studies would benefit from a total organic fluorine (TOF) determination. Presented work was aimed at developing a method for TOF determination. TOF is determined as an amount of inorganic fluoride obtained after defluorination reaction conducted off-line using sodium biphenyl reagent directly on the sorbent without elution of retained analytes. Recovered fluoride was analyzed using flow-injection system with either fluorimetric or potentiometric detection. The TOF method was tested using perfluorocarboxylic acids (PFCA), including perfluorooctanoic acid (PFOA), as model compounds. Considering low concentrations of PFAS in natural samples, solid-phase extraction as a preconcentration procedure was evaluated. Several carbon-based sorbents were tested, namely multi-wall carbon nanotubes, carbon nanofibres and activated carbon. Good sorption of all analytes was achieved and defluorination reaction was possible to carry out directly on a sorbent bed. Recoveries obtained for PFCAs, adsorbed on an activated carbon sorbent, and measured as TOF, were 99.5 ± 1.7, 110 ± 9.4, 95 ± 26, 120 ± 32, 110 ± 12 for C4, C6, C8, C10 and C12-PFCA, respectively. Two flow systems that would enable the defluorination reaction and fluoride determination in a single system were designed and tested.     

Flow-injection determination of iodide with a silver electrode

A procedure is developed for the flow-injection determination of iodide using a modified silver electrode; it extends the analytical range of iodide by an order of magnitude as compared to potentiometric determination using an iodide-selective electrode with a polycrystalline membrane. The detection limit is 7 μg/L. The procedure was used to determine iodide in natural mineral waters and model solutions. The throughput was 20–25 samples/h.     

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.     

Flow-injection spectrophotometric determination of salbutamol with 4-aminoantipyrine

A flow-injection method is proposed for the determination of salbutamol. The method involves the condensation of salbutamol with 4-aminoantipyrine in the presence of hexacyanoferrate (III) in alkaline medium, producing a coloured quinoneimide that was detected absorptiometrically at 500 nm.

The values of four variables (two reactor lengths and two reagent concentrations) were optimised by means of the sequential simplex method and their influence studied in univariant way.

The method was validated and compared with the HPLC method established in the United States Pharmacopeia (USP). Linearity was demonstrated in the range 0–74.1 mg/L of salbutamol sulfate (r² = 0.9999). Commercial samples of pharmaceuticals containing salbutamol sulfate (tablets and oral solutions) were analysed and the results obtained with the proposed method agreed with the USP method in less than 1.6%, with precision similar to the HPLC method (1%–2% R.S.D.). The sampling frequency was 75 samples/hour.     

Flow-injection spectrophotometric determination of trace vanadium based on catalysis of the gallic acid bromate reaction

High sensitivity is obtained by using high concentrations of gallic acid and bromate, although the uncatalyzed reaction is significant. Various reactant concentrations, reaction temperature, pH and residence times can be used to alter the linear calibration ranges and sensitivity for vanadium. With reagent streams of 1.76 M bromate and 0.06 M gallic acid at pH 3.8 (each at 1 ml min^?1), 0.2–20 ng of vanadium (20-μl injections) can be determined at 30°C. Oxidized gallic acid is detected at 380 nm. When the bromate concentration is decreased to 0.5 M and the temperature is 65°C, 0.05–4 ng of vanadium can be determined; the relative standard deviation is ca. 5% for 0.6 ng of vanadium. The toleranes for Al(III), Fe(III), Mo(VI) and iodide are 10 ng, 10 ng, 50 ng and 200 ng, respectively, for the determination of 1 ng of vanadium. About 12 samples can be injected per hour.