Comparison of soluble manganese(IV) and acidic potassium permanganate chemiluminescence detection using flow injection and sequential injection analysis for the determination of ascorbic acid in Vitamin C tablets

The limits of detection (3s) for ascorbic acid were 5×10⁻⁸ M with acidic potassium permanganate using both flow injection analysis (FIA) and sequential injection analysis (SIA) whereas the soluble manganese(IV) afforded 1×10⁻⁸ M and 5×10⁻⁹ M for FIA and SIA, respectively. Determinations of ascorbic acid in Vitamin C tablets were achieved with minimal sample pretreatment using a standard additions calibration and gave good agreement with those of iodimetric titration.     

Sequential injection analysis with second-order treatment for the determination of dyes in the exhaustion process of tanning effluents

A sequential injection (SI)-DAD spectrophotometric method to control the exhaustion of dyes in a mixture of three dyes from a tanning industry process has been developed. It is based on an interdiffusion process of the sample and reagents which leads to a gradual fall in pH through the channel to the detector recording a data matrix. The aim of this paper is to develop a second-order calibration model that is unaffected by interferents by applying multivariate curve resolution with alternating least squares (MCR-ALS). We obtained a linear calibration in the 5-30 mg l⁻¹ range with a correlation coefficient of 0.999 for each dye with detection limits of 2.6, 3.9 and 2.1 mg l⁻¹ for Acid Red, Acid Brown and Acid Orange, respectively. The simultaneous determination of the three dyes from tanning samples showed a satisfactory precision for the three analytes. The method has been validated comparing the concentration of some spiked samples with the expected concentration using a t-paired test. When we used this method to study the exhaustion of dyes, we found that there were several stages in this process. These data may be the key to optimising the exhaustion process.     

Highly sensitive gas-diffusion sequential injection analysis based on flow manipulation

The present paper describes approaches utilizing the powerful flow manipulation capabilities of sequential injection analysis (SIA) to substantially improve the efficiency of gas-diffusion separation compared to its traditional implementation in flow injection analysis (FIA). Ammonia, ethylamine, diethylamine and triethylamine were used as model analytes in this study. Eleven flow manipulation approaches involving continuous flow, stop-flow, oscillating flow, and the introduction of air bubbles to separate the sample zone from the donor solution were tested. Improvement in sensitivity compared to traditional gas-diffusion FIA exceeding one order of magnitude was achieved. It was observed that this improvement increased with the molecular size of the analyte.     

Flow injection analysis applied to a voltammetric electronic tongue

A measurement system, based on flow injection analysis (FIA) technique applied to a voltammetric electronic tongue is described. A reference solution was thus continuously pumped through a cell with a voltammetric electronic tongue, and test samples were injected into the flow stream. Responses were obtained by measuring the resulting pulse height. The FIA technique offered several advantages, since relative measurements are performed, the system is less influenced by sensor baseline drift, calibration samples and/or washing solutions can be injected within a measurement series, and the system is well adapted for automatization. The system was used to analyze standard solutions of H₂O₂, KCl, CuNO₃, K₄[Fe(CN)₆], K₃[Fe(CN)₆] and NaCl, and results obtained were treated with multivariate data analysis. Principal component analysis performed showed that electrode drift could be considerably decreased, and the set-up was also used for classification of different apple juices.     

A multicommuted flow system for sequential spectrophotometric determination of hydrosoluble vitamins in pharmaceutical preparations

A multicommuted flow system is proposed for spectrophotometric determination of hydrosoluble vitamins (ascorbic acid, thiamine, riboflavine and pyridoxine) in pharmaceutical preparations. The flow manifold was designed with computer-controlled three-way solenoid valves for independent handling of sample and reagent solutions and a multi-channel spectrophotometer was employed for signal measurements. Periodic re-calibration as well as the standard addition method was implemented by using a single reference solution. Linear responses (r=0.999) were obtained for 0.500-10.0 mg l⁻¹ ascorbic acid, 2.00-50.0 mg l⁻¹ thiamine, 5.00-50.0 mg l⁻¹ riboflavine and 0.500-8.00 mg l⁻¹ pyridoxine. Detection limits were estimated as 0.08 mg l⁻¹ (0.5 μmol l⁻¹) ascorbic acid, 0.8 mg l⁻¹ (2 μmol l⁻¹) thiamine, 0.2 mg l⁻¹ (0.5 μmol l⁻¹) riboflavine and 0.1 mg l⁻¹ (0.9 μmol l⁻¹) pyridoxine at 99.7% confidence level. A mean sampling rate of 60 determinations per hour was achieved and coefficients of variation of 1% (n=20) were estimated for all species. The mean reagent consumption was 25-fold lower in relation to flow-based procedures with continuous reagent addition. Average recoveries between 95.6 and 100% were obtained for commercial pharmaceutical preparations. Results agreed with those obtained by reference methods at 95% confidence level. The flow system is suitable for application in quality control processes and in dissolution studies of vitamin tablets.     

Reversed flow injection and sandwich sequential injection methods for the spectrophotometric determination of copper(II) with cuprizone

Two new flow methods, flow injection analysis (FIA) and sequential injection analysis (SIA), for the spectrophotometric determination of Cu(II) in water at trace levels have been developed and optimised. Both methods are based on the reaction with oxalic acid bis(cyclohexylidene hydrazide) (cuprizone) in alkaline media. The two procedures have been developed for the final aim to compare their performances and to offer new rapid heavy metals analysis tools, avoiding the use of extraction steps. A detailed study of the physico-chemical parameters affecting the systems performances has been carried out. The reversed FIA and sandwich SIA approaches offered the best sensitivity. In both cases, an extremely good linearity has been obtained within the range 0.06-4 μg ml⁻¹ (correlation coefficient r=0.9999), whereas the observed detection limits were 0.013 and 0.004 μg ml⁻¹, for FIA and SIA, respectively. Furthermore, due to the great similarity of the diffusion zones in the reaction slugs, our approach offers the opportunity to compare the two methods in analogous conditions. This SIA method, besides keeping its typical reagent saving features, offered analytical performances equivalent to those of FIA. To obtain these results, an original “stop-flow like” method was successfully employed in the SIA approach. Both methods were validated by analysis of real water samples, after copper addition, and certified reference samples of fortified and waste waters.     

Review: Highlights in recent applications of electronic tongues in food analysis

This paper examines the main features of modern electronic tongues (e-tongues) and their most important applications in food analysis in this new century. The components of an e-tongue (automatic sampler, array of chemical sensors, and data processing system) are described. Applications commented include process monitoring, freshness evaluation and shelf-life investigation, authenticity assessment, foodstuff recognition, quantitative analysis, and other quality control studies. Finally, some interesting remarks concerning the strengths and weaknesses of e-tongues in food analysis are also mentioned.     

Sequential injection system with higher dimensional electrochemical sensor signals Part 2. Potentiometric e-tongue for the determination of alkaline ions

An intelligent, automatic system based on an array of non-specific-response chemical sensors was developed. As a great amount of information is required for its correct modelling, we propose a system generating it itself. The sequential injection analysis (SIA) technique was chosen as it enables the processes of training, calibration, validation and operation to be automated simply. Detection was carried out using an array of potentiometric sensors based on PVC membranes of different selectivity. The diluted standard solutions needed for system learning and response modelling are automatically prepared from more concentrated standards. The electrodes used were characterised with respect to one and two analytes, by means of high-dimensionality calibrations, and the response surface of each was represented; this characterisation enabled an interference study of great practical utility. The combined response was modelled by means of artificial neural networks (ANNs), and thus it was possible to obtain an automated electronic tongue based on SIA. In order to identify the ANN which provided the best model of the electrode responses, some of the network's parameters were optimised and its usefulness in determining NH₄⁺, K⁺ and Na⁺ ions in synthetic samples was then tested. Finally, it was used to determine these ions in commercial fertilisers, the obtained results being compared with reference methods.     

Simultaneous determination of penicillin and ampicillin by spectral fibre-optical enzyme optodes and multivariate data analysis based on transient signals obtained by flow injection analysis

A multicomponent detection system using optical biosensors and flow injection analysis is described. The analysis of mixtures containing penicillin and ampicillin was realised by evaluating dynamic measurements of Phenol Red spectra in penicillinase optodes in combination with a diode array spectrometer. A variety of optodes has been produced by changing the composition of the receptor gel and the working pH. A set of characteristic quantities (describing dynamic and static features) could be obtained for each optode. These were used to compare the predictivity of classical multivariate calibration methods as well as of an artificial neural network. In addition, different algorithms were applied for the evaluation of the spectral data in order to select the most appropriate method for feature extraction. In consequence, the information obtained from the multivariate calibration models was used to set up an optimal sensor array consisting of four optodes with different types of penicillinase at different working pH.     

Use of sequential injection analysis to construct an electronic-tongue: application to multidetermination employing the transient response of a potentiometric sensor array

An electronic tongue based on the transient response of an array of non-specific-response potentiometric sensors was developed. A sequential injection analysis (SIA) system was used in order to automate its training and operation. The use of the transient recording entails the dynamic nature of the sensor's response, which can be of high information content, of primary ions and also of interfering ions; these may better discriminated if the kinetic resolution is added. This work presents the extraction of significant information contained in the transient response of a sensor array formed by five all-solid-state potentiometric sensors. The tool employed was the Fourier transform, from which a number of coefficients were fed into an artificial neural network (ANN) model, used to perform a quantitative multidetermination. The studied case was the analysis of mixtures of calcium, sodium and potassium. Obtained performance is compared with the more traditional automated electronic tongue using final steady-state potentials.     

Tubular potentiometric detector used to determine As(V) in sediment extracts by flow injection

The construction and evaluation of a tubular potentiometric detector sensitive to As(V) ions is described. This electrode, with no inner reference solution, is comprised of a FeOOH–SiO₂–graphite composite agglutinated with an epoxy resin. For As(V) ion concentrations in the range 1.0?×?10^?5 to 1.0?×?10^?1?mol?L^?1, the sensor is used as the selective electrode in an FIA system along with a commercial Ag/AgCl reference electrode. In optimal conditions, the practical limit of detection is 4?×?10^?6?mol?L^?1 and a sampling rate of 40?h^?1 can be achieved. The system was applied to estimate As(V) levels in sediments of a drinking water distributor in Zimapán (Mexico), an area known to be polluted with this element. The As(V) concentrations detected in the different extracts of sediments generated by the sequential modified BCR three-step extraction procedure (BCR-SEP) were comparable to those obtained by electrothermal atomic absorption spectroscopy (ET-AAS).     

Ultra-simple adaptor to convert batch cells with mercury drop electrodes in voltammetric detectors for flow analysis

A simple, robust and fast-responding flow adaptor for mercury drop electrodes (MDEs) is described. An L-shaped PTFE tube with an internal diameter of 0.5 mm is fixed with a silicone ring on the glass capillary of a MDE, in such a way as to direct the outcoming flow onto the mercury drop, from a distance of about 0.5 mm. Any commercial or laboratory-made batch cell, provided with an MDE, serves for the purpose. The level of supporting electrolyte in the cell is maintained constant through a siphon or a lateral draining orifice. The adaptor is compatible with all the different brands and operating modes of the MDEs (free dropping, controlled drop time, renewable static drop, hanging drop or sessile drop). Flow injection experiments were conducted with the following amperometric detection modes: sampled-DC, reverse pulse amperometry (RPA), and anodic stripping voltammetry (ASV). The FIA-RPA peaks presented a R.S.D.<0.8% for 1.0×10⁻⁵ mol l⁻¹ lead(II) (N=30, V_sample=100 μl). The response time (0-63% of the signal maximum) to a concentration step is 1.2 s for 500 μl injections of 0.1 mmol l⁻¹ ascorbic acid in acetate buffer at a flow rate of 1 ml min⁻¹, which corresponds to a response volume of 20 μl. As an example of practical application, copper(II) was determined in fertilizers by RPA using the standard addition method, at an analytical frequency of 90 injections per h.     

流动注射化学发光法测定佐米曲谱坦

在碱性条件下,佐米曲谱坦对鲁米诺-K3[Fe(CN)6]化学发光体系有较强的抑制作用,据此建立了佐米曲谱坦的流动注射化学发光分析法。该法的化学发光抑制值ΔI与佐米曲谱坦质量浓度在2.0×10-6~1.2×10-4g/mL范围内,呈良好的线性关系,检出限为7.6×10-7g/mL。对2.5×10-5g/mL佐米曲谱坦测定的相对标准偏差为1.2%(n=11)。方法适用于佐米曲谱坦片中佐米曲谱坦的测定。     

Sequential injection system with higher dimensional electrochemical sensor signals Part 1. Voltammetric e-tongue for the determination of oxidizable compounds

A sequential injection analysis (SIA) system was developed with the aim of obtaining an automatic and versatile way to prepare standards needed in the study of systems with higher dimensional sensor signals. To illustrate this, different analytical techniques were used in determinations of several analytes. Automated potentiometric calibrations of different potentiometric sensors, with and without interference, were carried out. Useful determinations of selectivity coefficients with two degrees of freedom were obtained. Simultaneous voltammetric determinations have also been done. Firstly, simultaneous determinations of lead and cadmium, using epoxy-graphite composite as the working electrode, have enabled a separate calibration for each metal to be obtained. Next, a voltammetric electronic tongue was designed and applied to the determination of oxidizable species. The use of artificial neural networks has solved the overlapped signal of ascorbic acid, 4-aminophenol and 4-acetamidophenol (paracetamol). A set of 63 data points was prepared automatically and has facilitated the training of an electronic tongue for these three analytes. Accurate predictions of test solutions, in the range of 12–410 μM for ascorbic acid, 17–530 μM for 4-aminophenol and 10–420 μM for paracetamol, have been achieved with RMSEs lower than 0.10 μM.     

顺序注射分析及其应用

本文回顾了顺序注射分析的发展过程,对其概念,理论、技术及应用进行了综述,上用文献七十会篇。     

Automatic flow systems based on sequential injection analysis for routine determinations in wines

Sequential injection systems for wine analysis have been developed in recent years for determination of more than 20 species. Several aspects of these systems are reviewed in the present paper. Special focus is given to implementation of in-line sample treatment and adaptation of system operation through software control to enable determination in different types of wine. The strategies used to enhance selectivity and the capacity for multi-parameter determination are also addressed.     

流动注射化学发光法测定甲硝唑

在碱性条件下 ,铁氰化钾氧化鲁米诺产生化学发光 ,甲硝唑对该体系有显著的增强作用 (亚铁氰化钾存在时 )。基于此 ,建立了流动注射化学发光测定痕量甲硝唑的新方法。甲硝唑浓度在 2 .0× 1 0 -6～ 4 .0× 1 0 -4 mol L范围内与发光强度呈良好的线性关系 ;检出限 (3σ)为 1 .5× 1 0 -7mol L。相对标准偏差 (c =1 .0× 1 0 -5mol L ,n=1 1 )为 3.6 %。方法已用于制剂中甲硝唑含量测定     

On-line determination of mercury(II) by membrane separation flow injection analysis

A rapid and inexpensive gas-diffusion (GD) flow injection method for the on-line determination of Hg(II) in aqueous samples is described. The analytical procedure involves the injection of a Hg(II) sample into a 1.5 M H₂SO₄ carrier stream which is merged with a reagent stream containing 0.6% SnCl₂ and 1.5 M H₂SO₄. Under these conditions Hg(II) is reduced to metallic mercury which partially evaporates through a Teflon membrane into an acceptor stream containing 1.75×10⁻⁴ M KMnO₄ in 0.3 M H₂SO₄. The decrease in the absorbance of the acceptor stream at 528 nm corresponding to the absorption maximum of the permanganate anion can be related to the original concentration of Hg(II) in the sample. The method is characterized by a detection limit of 4 μg l⁻¹ and a sampling frequency of 8 h⁻¹. The flow system was successfully applied to the analysis of river samples spiked with Hg(II).     

Trends of flow injection sample pretreatment approaching the new millennium

The important role of flow injection (FI) techniques for the automation, acceleration and miniaturization of solution handling in sample pretreatment as well as some recent trends in the development of the field are discussed, illustrated mainly by recent achievements in the author’s laboratory, including: (a) sample pretreatment for vapor generation and electrothermal AAS based on sequential injection (SI) techniques, with low reagent consumption and enhanced ruggedness; (b) combination of FI and SI sample pretreatment (filtration, dialysis, gas diffusion, column sorption) with capillary electrophoresis (CE) giving enhanced reproducibility and efficiency; (c) application of on-line microdialysis in in vivo monitoring of blood glucose in test animals and (d) application of on-line microdialysis and solvent extraction in continuous monitoring of drug dissolution processes with high resolution of process events. Future perspectives of FI sample pretreatment are discussed, emphasizing the improvement in ruggedness of the equipment and methods, the combination and synchronization of different means for liquid propulsion, and the development of miniaturized systems.     

流动注射化学发光法测定那格列奈

在碱性介质中,那格列奈对Luminol-H2O2体系的化学发光有很强的抑制作用,据此建立了流动注射化学发光抑制法测定那格列奈的新方法.该法的化学发光抑制值△I与那格列奈的质量浓度在2.0×10-8～1.0×10-6 g/mL范围内,呈良好的线性关系,检出限为1.4×10-8 g/mL;对4.0×10-7 g/mL那格列奈连续进行11次平行测定,相对标准偏差为1.0%;通过对荧光光谱的研究,对机理进行了初步探讨.