Comparison of Glassy Carbon and Copper Microparticles as a Renewable Working Electrode Material for Amperometric Determination of Amino Acids Using Flow Through Detector

Flow‐through detector with renewable working material based on glassy carbon or copper microparticles was used for flow injection determination of tyrosine by direct oxidation and phenylalanine via the complexation reaction with copper ions, respectively. Copper‐based detector allows the determination of electrochemically inactive amino acid, but the detection conditions are limited and fabrication and handling of the detector are more demanding. Low working potential, applied for the detection on copper microparticles, makes the determination very selective. Moreover, low baseline noise compensates lower sensitivity of copper‐based detector, enabling to reach quantification limit 4.7×10^?6 mol L^?1, in comparison with quantification limit 1.6×10^?6 mol L^?1 obtained for tyrosine on carbon‐based detector.     

Low pressure ion chromatography with a low cost paired emitter-detector diode based detector for the determination of alkaline earth metals in water samples

The use of a low pressure ion chromatograph based upon short (25 mm × 4.6 mm) surfactant coated monolithic columns and a low cost paired emitter-detector diode (PEDD) based detector, for the determination of alkaline earth metals in aqueous matrices is presented. The system was applied to the separation of magnesium, calcium, strontium and barium in less than 7 min using a 0.15 M KCl mobile phase at pH 3, with post-column reaction detection at 570 nm using o-cresolphthalein complexone. A comparison of the performance of the PEDD detector with a standard laboratory absorbance detector is shown, with limits of detection for magnesium and calcium using the low cost PEDD detector equal to 0.16 and 0.23 mg L⁻¹, respectively. Finally, the developed system was used for the determination of calcium and magnesium in a commercial spring water sample.     

Supported liquid membrane work-up in combination with liquid chromatography and electrochemical detection for the determination of chlorinated phenols in natural water samples

Summary A sample preparation method has been developed for the determination of chlorinated phenols in water. The method is based on a supported liquid membrane extraction system connected on-line to liquid chromatography with electrochemical detection. The supported liquid membrane technique utilizes a porous PTFE membrane. The membrane is impregnated with an organic solvent which forms a barrier between two aqueous phases and enables selective extraction. The technique can easily be coupled in a flow system. In this investigation five chlorinated phenols (1–5 chlorine atoms) were extracted from natural water samples. Extraction for 30 minutes resulted in detection limits of approximately 25 ng L^–1.     

The application of strongly reducing agents in flow injection analysis : Part 3. Vanadium(II)

The application of vanadium(II) as a powerful reducing reagent in flow injection analysis is described. Results are presented for the determination of various organic and inorganic substances. With spectrophotometric detection, based on the absorption by vanadium(II)-EDTA at 350 nm, limits of determination were about 5 X 10^?5 mol 1^?1. Nitrate, nitrite and hydroxylamine were measured with amperometric detection. The limit of determination was about the same as with spectrophotometric detection. In a slightly acidic medium, hydrazine could be determined with the amperometric detector, with a limit of determination of about 10^?4 mol l^?1. By coupling an ammonia detection device to the reduction system, the percentage conversions of nitrate, nitrite and hydroxylamine to ammonia were shown to be 26%, 54% and 47%, respectively.     

Amberlite XAD resin solid-phase extraction coupled on-line to a flow injection approach for the rapid enrichment and determination of phenols in water and waste waters

A novel and expeditious approach for direct determination of phenols in water and waste waters based on solid-phase extraction coupled on-line to a flow injection analysis (FIA) manifold is described. The method employs on-line preconcentration of the phenols in an acidified sample (pH=2.0) onto a 3 cmx3 mm column packed with Amberlite XAD-4 resin. The phenols are subsequently eluted from the resin into a flowing system with an alkaline solution (pH=13) by actuating a switching valve; the eluted analytes were then quantified spectrophotometrically as the products of reaction with 4-aminoantipyrine (4-AAP) and potassium ferricyanide on passing through the flow-cell of a detector. The proposed method has a linear calibration range 0.01-1 mug ml(-1) of phenol, with a detection limit of 0.004 mug ml(-1) (S/N=3) and a sample throughput of 12 h(-1), investigated with a 4.4 ml sample volume. The relative standard deviation is 2.4% for 0.2 mug ml(-1) of the analyte. The sensitivity offered by the procedure was higher by a factor of 13 than that provided by a conventional flow injection analysis method. The analytical scheme of the proposed system is much simpler than its conventional manual counterpart due to the fact that it combines trace enrichment, sample clean-up, derivation and detection in one analytical set-up. The high speed, ease of use and automation, selectivity, and relative freedom from random contamination by sample handling make this method ideal for the phenols monitoring in water and waste waters.     

Flow-injection determination of nonylphenol in liquid media using a piezoelectric immunosensor

A piezoelectric flow immunosensor for the rapid determination of nonylphenol in aqueous solutions was developed. An aminophenol-protein conjugate (4-AP-GA-BSA) immobilized on the presilanized surface of a silver electrode was used as a bioreceptor coating of the sensor. The effects of the nature and concentration of monoclonal and polyclonal antibodies on the analytical signal of the sensors were studied; the activity of immunoreagents was evaluated based on the binding constants K _b. The cross reactions of various phenols with antibodies were studied and the cross reaction percentages were found. A procedure for the flow-injection determination of nonylphenol in liquid media was developed using a piezoelectric immunosensor as a detector. The calibration graph was linear over the concentration range 1–20 ng/mL; the detection limit for nonylphenol was 0.8 ng/mL.     

Application of correlation high-performance liquid chromatography to the reverse-phase separation of traces of chlorinated phenols

A correlation high-performance liquid chromatography instrument operating under online microprocessor control is described. Pentachlorophenol (PCP) and 11 other polychlorinated phenols are separated on a reverse-phase system. With an ultraviolet detector, the detection limit is about 2.5 × 10^-7 absorption unit (about 6 μg PCP l^-1 at 254 nm).     

An improved flow system for phenols determination exploiting multicommutation and long pathlength spectrophotometry

A greener and sensitive procedure for spectrophotometric determination of phenols based on a multicommuted flow system with a 100 cm optical path flow cell is presented. The method exploited the oxidative coupling of phenolic compounds with 4-aminoantipyrine in alkaline medium containing potassium hexacyanoferrate(III). Sensitivity was 80-fold higher than that achieved with a 1 cm flow cell, making feasible the determination of phenols in the 10-100 μg l⁻¹ range with a detection limit estimated as 1 μg l⁻¹ phenol. The sampling rate and the coefficient of variation were estimated as 90 determinations per hour and 0.6% (n=10), respectively. The multicommutation approach allowed a 200-fold reduction of the reagent consumption in comparison with the reference batch method. Moreover, the chloroform extraction for analyte concentration is unnecessary in view of the increase in sensitivity. Recoveries within 93.3 and 106% were achieved for determination of phenol in natural and wastewater samples. Results agreed with the obtained by a reference method at the 95% confidence level.     

Organic-Phase Enzyme Electrode for the Determination of Phenols in Olive Oils

Abstract

A rapid procedure for determining phenols in olive oils, based on an organic-phase enzyme electrode, is described. Direct assays are performed in chloroform solutions which support the tyrosinase activity. This class (phenol)-specific enzyme strongly adheres to the surface of the graphite transducer. The resulting wall-jet detector offers effective flow injection operation, with a detection limit of 4×10^?7 M (0.8 ng) phenol and sample frequency of 60 h^?1. Applicability to olive-oil samples of different origins is illustrated.     

Sequential injection technique for determination of phenoxybenzamine hydrochloride and metoclopramide in pharmaceutical formulations

A sequential injection analysis (SIA) system is described for the determination of phenoxybenzamine hydrochloride and metoclopramide using spectrophotometer as detector. The method is based on the detection of an unstable red intermediate compound resulting from the reaction of phenoxybenzamine hydrochloride or metoclopramide with the diazotizating product of p-phenylenediamine with sodium nitrite in hydrochloric acid medium. The sampling frequency is 69 h⁻¹ and 75 h⁻¹ for phenoxybenzamine hydrochloride and metoclopramide, respectively. The linear range is 10–400 μg/mL for phenoxybenzamine hydrochloride with a detection limit of 0.081 μg/mL and 20–250 μg/mL for metoclopramide with a detection limit of 0.034 μg/mL. The RSD is 1.01 and 0.45% for phenoxybenzamine hydrochloride and metoclopramide, respectively. The proposed methods were used to determine phenoxybenzamine hydrochloride and metoclopramide in pharmaceuticals. The results are compared with those obtained by pharmacopoeia method. The article is published in the original.     

Amperometric biosensor for oxalate determination in urine using sequential injection analysis

An amperometric flow biosensor for oxalate determination in urine samples after enzymatic reaction with oxalate oxidase immobilized on a modified magnetic solid is described. The solid was magnetically retained on the electrode surface of an electrode modified with Fe (III)-tris-(2-thiopyridone) borate placed into a sequential injection system preceding the amperometric detector. The variables involved in the system such as flow rate, aspired volumes (modified magnetic suspension and sample) and reaction coil length were evaluated using a Taguchi parameter design. Under optimal conditions, the calibration curve of oxalate was linear between 3.0-50.0 mg·L^-1, with a limit of detection of 1.0 mg·L^-1. The repeatability for a 30.0 mg·L^-1 oxalate solution was 0.7%. The method was validated by comparing the obtained results to those provided by the spectrophotometric method; no significant differences were observed.     

Microwave induced plasma atomic emission spectrometry: a suitable detection system for the determination of volatile halocarbons

Microwave induced plasma atomic emission spectrometry (MIP-AES), a highly sensitive detection system for organometal compounds, was coupled to an automated purge and trap gas chromatographic system for the determination of volatile halogenated hydrocarbons in environmental water samples. Optimisation of the parameters affecting the injection and detection system led to relative detection limits from 1 to 14 ng · L^–1 for chlorine- and bromine-compounds and from 10 to 75 ng · L^–1 for iodine-compounds, on basis of a 10 mL sample volume. A comparison of the analytical characteristics between atomic emission detection (AED) and electron capture detection (ECD) showed a lower sensitivity of the atomic emission detector for halocarbons, but the detection thresholds are low enough to use the method for the determination of volatile halocarbons in trace level concentrations. The ability of the atomic emission detector provides increased selectivity for monitoring individual halogenated compounds under simplified and rapid chromatographic conditions, within a total analysis time of only 30 min. The method was applied with gas chromatographic separation for the analysis of sea water samples. Concentrations for the different elements between 0.05 and 15.28 μg · L^–1 were determined.     

High performance liquid chromatography determination of chlorophenols in water samples after preconcentration by continuous flow liquid membrane extraction on-line coupled with a precolumn

A continuous flow liquid membrane extraction (CFLME)-C₁₈ precolumn-liquid chromatography system was developed for preconcentration and determination of chlorinated phenols (CPs). After preconcentration by CFLME, which is based on the combination of continuous flow liquid-liquid extraction and supported liquid membrane, CPs were enriched in 960 μl of 0.5 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto the C₁₈ analytical column for separation and detected at 215 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor concentration were optimized. The proposed method presents detection limits of 0.02-0.09 μg l⁻¹ (S/N=3) when 100 ml samples were enriched. The proposed method was successfully applied to determine CPs in tap water and river water samples with spiked recoveries in the range of 70-121%.     

Analysis of Follicle-Stimulating Hormone by CE with Chemiluminescence Detection Based on Competitive Immunoassay

A competitive immunoassay and capillary electrophoresis with enhanced chemiluminescence detection have been used for determination of follicle-stimulating hormone (FSH) in human serum. The method is based on the competitive immunochemical reaction of FSH and horseradish peroxidase (HRP)-labeled FSH with anti-FSH, CE separation of antibody-bound and free HRP-labeled FSH, then chemiluminescence detection. The detection limit depends on the stability of the immune complex, which depends on analysis time and detector design, and on the chemiluminescence enhancer used. A unique chemiluminescence detector without dead volume or diluent effects was therefore used, and sodium tetraphenylboron was selected as the optimum enhancer. As a result sensitivity was substantially improved. Free HRP-labeled FSH and the immune complex could be separated within 15 min in alkaline borate buffer by use of a potential of 15 kV. Under the optimum conditions a calibration plot for FSH was established in the concentration range 0–100 mIU mL⁻¹; the detection limit was 0.06 mIU mL⁻¹. The concentration sensitivity achieved was 30 times better than that of ELISA.     

Determination of Phenols In Natural Waters with A Flow-Analysis Method and Chemiluminescence Detection

ABSTRACT

A simple flow-manifold with time based sample introduction system was elaborated and used to determine phenols in natural waters. Use of computer controlled solenoid valves and direct chemiluminescence detection enables very low reagent consumption. A quantity of less than 1.5 μmol of potassium permanganate and 600μmol of sulphuric acid per determination is used. The use of on-line preconcentration column filled with XAD-4 resin enables determination with the detection limit of 5 ng-ml^?. The sample throughput is 12-h^? when the column is used and 60-h^? without a column.     

A chemiluminescence flow injection system for nitrite ion determination

A chemiluminescence system is described for the determination of nitrite ion based on new designs for an ozone generator, liquid-gas separator and chemiluminescence reaction cell. The method is based on the gas-phase chemiluminescence reaction between ozone and nitric oxide, which is generated from the reduction of nitrite with iodide in sulfuric acid solution. The efficiency of the system was evaluated by investigation of the analytical performance characteristics of the system for nitrite determination in batch and flow injection procedures. Under optimal conditions, the chemiluminescence response of the system was linear against the nitrite concentration over the range 1 to 1 × 10⁴ ng ml^?1 in the batch procedure and 10 to 5 × 10³ ng ml^?1 in the flow injection procedure, with detection limits of 1 and 10 ng ml^?1, respectively. The method is highly selective and allows for the determination of nitrite in the presence of high concentrations of several cationic, anionic and nitrogen containing species. It has been successfully applied to the analysis of nitrite in natural water and soil extracts.     

Multicommutated Flow System with Amperometric Detection. Determination of Uric Acid in Urine

In this work an automated flow methodology based on a tubular amperometric detector coupled to a multicommutated flow system was developed and applied in the determination of uric acid in urine. The exploitation of the analytical potential of multicommutated flow systems allowed the implementation of an expeditious and easily controlled on‐line sample dilution, based on the zone sampling approach. The dilution capability exhibited by the developed methodology allowed a direct insertion of the samples in the flow system, without any pretreatment, assuring faster, simpler and less expensive analyses when compared to the enzymatic based methods with spectrophotometric detection commonly used in clinical analyses. The results obtained with the developed system in the determination of uric acid in urine were compared with those obtained by the enzymatic method used in clinical analysis laboratories, and no statistical difference between both methods (for a confidence level of 95%) was found. The proposed system showed good repeatability (RSD<3%, n=10) and a detection limit of 4×10^?7 mol L^?1.     

Instrumentally simple flow detector for the determination of traces of electroluminescent compounds in aqueous solutions

A flow detector based on the observation of the cathodic electroluminescence at an oxide-covered aluminium electrode is described. The detector responds only to electroluminescent compounds in aqueous eluents, and additional selectivity can be achieved by making use of optical filters for wavelength discrimination. The optimum detection conditions were determined by using the cathodic electroluminescence induced by a polynuclear aromatic hydrocarbon in micellar solutions as the model electroluminescence. This instrumentally simple detector can be used to determine electroluminescent compounds in a wide concentration range with good precision. For instance, its detection limit, dynamic range and precision (i.e., relative standard deviation for 20 successive measurements of 1 × 10^?7 M samples) for the determination of micelle-encapsulated 9,10-diphenylanthracene were found to be 1 × 10^?8 M, four orders of magnitude and 7%, respectively.     

Implications of on-line FTIR detection in the separation of coal-derived products via HPLC with polar modifiers

Summary Fourier-transform infrared spectrometry (FTIR) was utilized as a detection system for high-performance liquid chromatography of polar compounds on a normal bonded-phase system. In addition to FTIR, UV (254 nm) and refractive index detection were employed in the separation of model compounds containing oxygen and nitrogen atoms in their molecules (phenols, alcohols, neutral and weakly basic nitrogen compounds). A polar amino-cyano (PAC) bonded-phase column was employed with a binary mobile phase (98:2 CDCl₃:CH₃CN). The separations and the information gained from each detector is discussed, including interactions between sample material and mobile phase. A polar fraction of a coal-derived product is also chromatographed under identical conditions. The results based on FTIR detection and chromatographic retention behavior suggest the exclusive presence of hindered and unhindered phenols.     

Coupled multisyringe flow injection/reactor tank for the spectrophotometric detection of azinphos methyl in water samples

A multisyringe flow injection system with spectrophotometric detection is presented as a fast, robust and low-reagent consumption system for the determination of azinphos methyl (AzMe) in water samples. Determination is based on the Griess reaction. The analyte is hydrolyzed and the reaction product reacts with nitrite in acid medium to form the diazonium salt that reacts further with 1-naphtol reagent to produce an azo compound. The azo derivative is spectrophotometrically monitored at 485 nm. The influence of several chemical and flow variables has been investigated. Under the optimum analytical conditions, the linearity of the calibration curve for AzMe ranges from 1 to 32 μg mL^?1. The detection limit is 0.17?µg mL^?1, and recoveries between 95 to 109% have been obtained. The repeatability (RSD) is 0.8% for a 10?μg mL^?1 solution, and the injection throughput is seven samples h^?1. The system has been satisfactorily applied to the determination of AzMe in spiked river and dam water samples. The results were in agreement at the 95% confidence level with those obtained by HPLC.