Flow Injection Analysis Detection Research Articles

Application of a Hexa‐Electrode Electrochemical Detector for Flow Injection Analysis

AbstractExtending from the development of dual‐electrode electrochemical detector, a hexa‐electrode electrochemical detector for use with the FIA was proposed. With this hexa‐electrode detector, the in‐series and in‐parallel modes of dual‐electrode can be easily performed either individually or simultaneously. Feasibility of the hexa‐electrode detector for repetitive analyses which would result in an enhancement of S/N ratio was demonstrated by running the square wave anodic stripping voltammetry (SWASV) analysis of cadmium. From the normalized linear calibration graph and the enhanced sensitivity obtained. applicability of the HED as a versatile electrochemical detector for flow injection analysis was confirmed.

A Versatile Computer-Controlled Amperometric Detector for High Performance Liquid Chromatography and Flow Injection Analysis

Abstract A low-cost battery-powered amperometric detector for Flow Injection Analysis and High Performance Liquid Chromatography has been developed. The potentiostat is controlled by a personal computer through an 8 bit Analog-to-Digital, Digital-to-Analog card. The electronic design of the potentiostat is based on high-gain low-power operational amplifiers. This configuration allowed us to use batteries as the power source, minimizing power source noise. The control program was developed in Turbo Pascal®. The cell current is plotted “on-line” on the screen as a function of time, and the actual potential is continuously monitored. Manuscript 1060

Detection of flow injection analysis with pH gradient by acousto-optic tunable filter based spectrophotometry

The instrumentation development of a spectrophotometer based on an acousto-optic tunable filter (AOTF) and its applications in a flow-injection (FI) system for gradient exploitation is described. This compact, all-solid state spectrophotometer which contains no-moving parts, can be scanned in the visible region (390–650 nm) at a speed of 300 nm/s. The fast scanning capability of the instrument made it possible to monitor the spectral response of an acid-base indicator mixture. The recorded spectra of the indicators were then converted to pH by means of a partial least square (PLS) multivariate calibration technique. With use of the same indicator mixture, the relationship obtained facilitates the determination of pH of any flow-injection pH gradient system which is produced by injecting a strong acid or base over a mixture of buffered solutions with a wide range of pH values. The time versus pH relationship can, therefore, be readily established for any buffer-reagent mixture flowing in the FI system. The FI system, which has been calibrated this way, can then be used to rapidly characterize the behavior of chemical systems as a function of pH. Two examples are demonstrated in this work: the determination of the p K a of the weak acids and of the complex formation between iron(III) and sulfosalicylic acid.

An Inexpensive Detector for Absorbance Measurements in Flow-Injection Analysis

A photometric transducer for peak detection in flow-injection analysis is described. It relies on a light-emitting diode as the light source and a photodiode as the detector. A logarithmic amplifier is used in order to emulate Beer-Lambert's Law and to directly obtain absorbance readings. The performance has been tested with two commonly employed flow-injection procedures, but the device should be suitable for most methods that may be used in the teaching lab.

Near-infrared detection of flow injection analysis by acoustooptic tunable filter-based spectrophotometry.

The instrumentation development of a near-infrared (near-IR) spectrophotometer based on an acoustooptic tunable filter (AOTF) and its application as a detector for flow injection analysis (FIA) are reported. In addition to being compact and all solid state, this AOTF-based instrument is very sensitive, has high resolution, and can be rapidly scanned. The latter advantage make it uniquely suited as a detector for FIA, in that it can rapidly record the whole near-IR absorption spectrum of a mixture passing through the FIA flow cell. Subsequent treatment of the recorded spectra with multivariate calibration methods makes it possible to use the FIA, for the first time, for such applications as the simultaneous determination of trace amounts of water and benzene in ethanol. Because all organic compounds absorb light in the near-infrared region, this AOTF-based near-IR detector can serve as a universal detector for FIA; as a consequence, applications of the FIA techniques can be expanded to other areas which are not possible otherwise.

Use of poly(ester-sulfonic acid) film-coated electrodes as amperometric detectors in flow injection analysis

Within the past several years significant advances have been made towards the development and incorporation of chemically modified electrodes as selective detectors for high performance liquid chromatography and flow injection analysis. In many cases the chemically modified electrode systems closely approach the “ideal” detector specifications of chemical and mechanical stability along with a significant linear response region. This paper will discuss the characterization and incorporation of ionomeric poly(ester-sulfonic acid) coated electrodes as nonaqueous electrochemical detectors. The orientation of the electrodes in the detector system as well as the increased sensitivity levels to 10 −10 g ml −1 for cationic species and 10 −9 g ml −1 for neutral species will be presented. Also the applicability of the ionomer coated electrodes as nonelectrolyte detectors achieved a reproducible response with detection limits to 10 −6 g ml −1. Overall this system performed as well as, or better than, more specialized and expensive thin layer electrochemical detectors.

Potentials of chemiluminescence detection in flow injection analysis: Determination of penicillamine applying a quinine‐Ce (IV) system

Potentials of chemiluminescence detection in flow injection analysis: Determination of penicillamine applying a quinine‐Ce (IV) system

Electrochemical detection in flow injection analysis for determining serum lipase activity

Abstract As a simple and rapid method for serum lipase determination, assessment was made of electrochemical detection in flow injection analysis (FIA), by measuring the voltammetric prepeak accompanied by the reduction of 2-methyl-1, 4-naphthoquinone (vitamin K 3 , VK 3 ) due to the effect of free fatty acids. A sample containing lipase was incubated with olive oil as the substrate at 37 °C for 10 min to bring about the release of fatty acids. The sample solution was prepared by dissolving the oily residue extracted by ether in ethanol solution containing 3 mM VK 3 and 38 mM LiCIO 4 . A 5 μl aliquot of the sample solution was injected into the flow injection (FI) system. The peak height of the flow signal was linear to lipase activity between 10 and 1000 U l −1 and RSD was 1.2% for 70 U l −1 ( n = 5). By this method, as many as 30 samples h −1 can be processed, thus showing this method to be useful and highly efficient.

Monitoring of pyrocatechol indoor air pollution

Spectrophotometric and electrochemical methods for monitoring of pyrocatechol (PC) indoor air pollution have been investigated. Spectrophotometric determination was performed using Fe(III) and iodine methods. The adherence to Beer's law was found in the concentration range between 0 and 12 μg ml − for iodine method at pH = 5.7 measuring absorbance at 725 nm, and in the range 0–30 μg ml − for Fe(III) method at pH = 9.5 measuring absorbance at 510 nm. The former method showed greater sensitivity than the latter one. Differential pulse voltammetry (DPV) and chronoamperometric (CA) detection in flow injection analysis (FIA) using carbon paste electrode in phosphate buffer solution of pH = 6.5 was also used for pyrocatechol determination. The electrochemical methods allowed pyrocatechol quantitation in submicromolar concentration level with an overall reproducibility of ± 1%. The efficiency of pyrocatechol sampling collection was investigated at two temperatures (27 and 40°C) in water, 0.1 M NaOH and 0.1 M HCl solutions. Solution of 0.1 M HCl gave the best collection efficiency (95.5–98.5%). A chamber testing simulating the indoor pollution has been performed. In order to check the reliability of the proposed methods for monitoring of the indoor pyrocatechol pollution, the air in working premises with pyrocatechol released from meteorological charts during mapping and paper drying was analyzed using proposed methods. The concentration of pyrocatechol in the air during mapping was found to be 1.8 mg m −3 which is below the hygienic standard of permissible exposure of 20 mg m −3 (≈ 5 ppm). The release of pyrocatechol from the paper impregnated with pyrocatechol standing at room temperature during one year was also measured. The proposed methods can be used for indoor pyrocatechol pollution monitoring in working premises of photographic, rubber, oil and dye industries, fur and furniture dyeing and cosmetic or pharmaceutical premises where pyrocatechol and related compounds are in use.

Amperometric Determination of N-Nitrosamines in Aqueous Solution at an Electrode Coated with a Ruthenium-Based Inorganic Polymer

The diffusion-limited electrochemical oxidation of N-ni-trosamines in an aqueous pH 1.5 buffer is demonstrated at a glassy carbon electrode which is coated with a film of mixed valent ruthenium oxides that are stabilized by cyano cross-links (mvRuCN). The process occurs at 1.080V vs Ag/AgCl, 3M Nacl where Ru(VI) is the electron-transfer mediator in the film. The mvRuCN electrode was used in a potentiostatic amperometric detector for flow injection analysis and high-performance liquid chromatography to allow the determination of representative compounds such as N-nitrosodimethylamine, N-nitrosodi-n-propylamine (NNDPA), and N-nitrosodiphenylamine (NNDPhA)

Flow-injection analysis with bulk extraction based optical sensor membranes

The use of recently described optical sensing membranes as solid phase photometric detectors in flow-injection analysis is described. These membranes are based on ionophores and lipophilic pH indicators contained in poly(vinyl chloride). The flow-injection mode of operation not only automates measurements with these optode membranes but also allows on-line mixing of the samples with pH buffer. The method therefore represents a good solution to the pH cross-sensitivity of the membranes. Absorbance measurements were carried out with a light emitting diode/photodiode transducer which was connected directly to an integrated circuit logarithmic amplifier. This inexpensive detector system allows highly precise absorbance measurements. It is further demonstrated that simultaneous measurements can easily be carried out with a slightly modified assembly.

A new spectroelectrochemical cell for flow injection analysis and its application to the determination of Fe(II) down to the femtomol level by surface-enhanced resonance Raman scattering (SERRS)

A spectroelectrochemical cell that uses surface-enhanced Raman scattering (SERS) for detection in flow injection analysis (FIA) is presented. The SERS-active surface is generated in situ by the electrochemical deposition of a silver film on a glassy carbon electrode. The electrode surface can be cleaned and renewed in situ between consecutive analytical determinations of adsorbates on the silver layer by anodic stripping of the used film and the deposition of a new one. Comparison with a flow cell, using a bulk silver electrode shows that, depending on the analyte, the silver electrode surface cannot be cleaned in situ. The potential applicability of the cell was demonstrated by determining Fe(II) in the form of [Fe(bipy) 3] 2+ (bipy = 2,2′-bipyridine) adsorbed on the silver-coated glassy carbon electrode. Iron has been detected at concentrations as low as 10 −9 M for an injected volume of 130 μl (femtomols of iron). Calibration curves were established in the concentration range from 10 −9 to 10 −5 M. The relative standard deviation of determination of Fe(II) at the 10 −9 M level was 10%.

Radiometric detection in flow-injection analysis (Radiometric Flow-Injection Analysis)

A single line system with a detector of radioactivity was used for the determination of60Co. In the determination, no additional chemistry is involved and limited dispersion is desirable. For this application, the FIA system is used only as a transport system for the sample up to the detector.

Development of a Novel Detector for Flow Injection Analysis Based on Optical Beam Deflection Induced by the Reaction Heat

A novel detector for flow injection analysis has been developed based on the optical beam deflection induced by the chemical reaction heat. A new flow cell was designed, in which the lower part is filled with CCU and an HCl solution is flowed above the CCU phase. An NaOH solution is injected into the flow line to react with the HCl. The neutralization heat is transferred to the CCU phase, thus generating a temperature gradient. This temperature gradient induces a refractive index gradient which, in turn, generates a deflection of a probe beam that is passed through the CCl4 phase. The effects of the flow rate and the length of the cell on the deflection signals have been investigated. The deflection signal was found to be proportional to the concentration of NaOH in the range of 0.05 to 0.5 mol/l by using the flow cell. The detection limit of the NaOH concentration was about 0.05 mol/l. Another type of the flow cell is also discussed. c]Changchun, p]China. c]Minami-Ohsawa, Hachioji, Tokyo o]192-03, p]Japan

Anion-selective electrodes based on a gold(III)-triisobutylphosphine sulfide complex

Ion-selective electrodes using poly(vinyl chloride) membranes impregnated with a gold(III)–triisobutylphosphine sulfide complex are described. These electrodes were characterized in both conventional and flow-through tubular configurations. The response of the electrodes was Nernstian for thiocyanate and tetrachloroaurate(III) and the detection limit was 1.1 × 10–6 mol dm–3. Flow-through tubular electrodes were used as potentiometric detectors in flow-injection analysis, resulting in a reproducible (peak heights within ± 1 mV for three repeated injections at a given concentration level) and rapid (sample throughputs around 80 h–1) technique for the determination of both anions.

An experiment using time-based detection in flow injection analysis

This experiment can be adopted to work with any number of reactions that result in a product that absorbs light of the LED wavelength significantly.

A photometric detector based on a blue light-emitting diode

The suitability of blue light-emitting diodes as radiation sources in molecular absorption spectroscopy was evaluated. Electronic as well as spectral considerations are discussed. A transducer based on a blue light-emitting diode and a photodiode is described which yields direct absorbance readings by passing the photocurrent to an integrated circuit logarithmic converter. The performance of this device was tested for commonly used spectrophotometric procedures for Cr, Mn, Zn, Fe and Cl and compared with conventional molecular absorption spectroscopy. Also investigated was the application of the transducer as a detector in flow-injection analysis.

Optical sensors in flow injection analysis

Representative examples are given on how optical chemical sensors (optrodes) can be coupled to flow injection systems to result in flow injection analyzers. These have served two main purposes so far, namely testing the performance of optrodes, and secondly as detectors in flow injection analysis (FIA). Specifically, the use of optrodes sensitive to pH, oxygen, ammonia and other chemical species as detectors in FIA will be described, all mainly in conjunction with enzymatic reaction schemes. Finally, optrodes are shown to be useful for determination of enzyme activity and enzyme inhibition by heavy metals.

Side-View Type of Waveguide Flow Cells for Fluorimetry as a Detector for Flow Injection Analysis of Lead

Several types of cells made of Pyrex® ( nD20 = 1.474) capillaries were constructed for fluorimetry from the standpoint of waveguiding of the excitation source. Fluorescence intensity detected from a vortex cell is virtually linearly dependent on the refractive index of the solvent containing the fluorophore. This type of cell is applied as the fluorimctric detector for the flow injection analysis of the lead(II) ion. The lead ion was incorporated into a macrocyclic ligand, cryptand 2.2.2, and the resulting compound was ion-paired with eosine (fluorescent dye). This complex ([Pb(cryptand 2.2.2)]eosine) was extracted into chlorobenzene ( nD20 = 1.5248) and was introduced into the above vortex cell. An Ar+ laser operated at 514.5 nm was used as the light source, and the fluorescence of eosine at 600 nm was detected. Two ng/mL of Pb(II) ion was obtained as the detection limit.

A reticulated vitreous carbon spectroelectrochemical detector for flow injection analysis and liquid chromatography

AbstractA spectroelectrochemical detector for flow injection and liquid chromatography is described. The detector design has dimensions of a standard 1 cm sample cuvette with a replaceable reticulated vitreous carbon working electrode. No special cell holder or modifications to the spectrophotometer are required to use the detector. Chronocoulometry is used to indicate a trend from thin‐layer behavior toward semi‐infinite diffusion behavior as the electrode pore size increases. Ferro‐/ferricyanide solutions were used to evaluate the flow injection characteristics of the detector. A sampling rate of 180 injections per hour was used. Linear calibration curves in the micromolar range were achieved with a reproducibility of 2–7%. A mixture of phenol, chlorophenols, and nitrophenols was used to investigated the simultaneous electrochemical and optical response for liquid chromatography.