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.     

Flow injection analysis of potassium using an all-solid-state potassium-selective electrode as a detector

The concentration of potassium was determined by a combination of flow injection analysis (FIA) with an all-solid-state potassium sensor detection. The all-solid-state potassium-selective electrode possessing long-term potential stability was fabricated by coating an electroactive polypyrrole/poly(4-styrenesulfonate) film electrode with a plasticized poly(vinyl chloride) membrane containing valinomycin. The simple FIA system developed in this laboratory demonstrated sensitivity identical to that in the batch system and achieved considerably rapid assay (150 samples h⁻¹). Analyses of soy sauce and control serum samples by this FIA system yielded results in good agreement with those obtained by conventional measurements.     

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.     

The Use of Chronoamperometry and Chemometrics for Optimization of Conducting Polymer Sensor Arrays

A general approach using principal component analysis was applied to amperometric data obtained from flow injection analysis (FIA) to select conducting electroactive polymers (CEPs) and applied potential waveforms for discrimination of potassium and methylamine. The results were compared with the selection from the application of the PCA approach for cyclic voltammetry data in our previous research. Good agreement between the two methods of selection was found, which indicates that within the general qualitative limits of the approach, PCA can be applied for selection of chemical and electrochemical parameters for FIA detection/discrimination using CEP sensor arrays detector for a range of analytes.     

流动注入吸附溶出—催化极谱氢波分析痕量铂

本文叙述一种流动注入吸附溶出一催化极谱测定痕量铂的新技术,它集中了溶出法、催化波和流动注入的优点,达到非常高的灵敏度和分析速度。实验给出了最佳载液组成、流速、注入体积、吸附富集电位和吸附时间等因素。本方法成功地进行了多种铂络合物、矿样和生物样品分析。     

A hybrid FIA/HPLC system incorporating monolithic column chromatography

We have combined the generation of solvent gradients using milliGAT pumps, chromatographic separations with monolithic columns and chemiluminescence detection in an instrument manifold that approaches the automation and separation efficiency of HPLC, whilst maintaining the positive attributes of flow injection analysis (FIA), such as manifold versatility, speed of analysis and portability. As preliminary demonstrations of this hybrid FIA/HPLC system, we have determined six opiate alkaloids (morphine, pseudomorphine, codeine, oripavine, ethylmorphine and thebaine) and four biogenic amines (vanilmandelic acid, serotonin, 5-hydroxyindole-3-acetic acid and homovanillic acid) in human urine, using tris(2,2′-bipyridyl)ruthenium(III) and acidic potassium permanganate chemiluminescence detection.     

Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis-UV-visible spectroscopy pyruvate determination

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min⁻¹, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L⁻¹ and hydrochloric acid concentration 0.5 mol L⁻¹. The working calibration range was extended from 80 mg L⁻¹ (Batch method) to 700 mg L⁻¹ with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r² = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.     

Flow injection spectrophotometric determination of copper in petroleum refinery wastewaters

This paper reports a new strategy for flow injection spectrophotometric Cu (II) determination in petroleum refinery wastewaters, exploring its reaction with sodium diethyldithiocarbamate (DDTC), without solvent extraction step, thus avoiding the use of harmful organic solvents. The influence of several chemical and flow variables was studied as well as the possible interferences. Under optimized conditions, the flow system was able to process 63 samples per hour, with a detection limit of 23 ng ml⁻¹ and a RSD of 2.1% at the 0.2 μg ml⁻¹ level. In order to attest the accuracy of the methodology, seven samples of effluents were analyzed by the proposed method and the results were compared with that obtained by FAAS. It was observed that the physical interferences verified in the FAAS procedure, which only permits its use by the standard addition method, were not present in the FIA procedure. The results obtained by FIA method were not statistically different from that obtained by FAAS-standard addition method. Also, the analysis of three spiked samples provided recovery percentages between 93 and 103%.     

Flow injection determination of histamine with a histamine dehydrogenase-based electrode

A flow injection analysis (FIA) system for the determination of histamine was developed using histamine dehydrogenase (HmDH)-based electrode. Histamine dehydrogenase was immobilized in an osmium-derivatized redox polymer, poly(1-vinylimidazole) complexed with Os(4,4′-dimethylbipyridine)₂Cl₂ (PVI-dmeOs), film on a glassy carbon electrode. As expected from the characteristics of this enzyme in a solution, this electrode exhibits high selectivity to histamine and is not sensitive to other primary amines including common biogenic amines, putrescine, cadaverine and tyramine. The detection limit for histamine was 100 pmol ( μl injection) at a S/N ratio of 3, and response linearity was retained up to 0.6 mM. The FIA system was successfully applied to the determination of histamine in fish samples. The performance of the FIA system is discussed and compared with a high-performance liquid chromatography (HPLC) method which is routinely used for histamine analysis.     

双光束流动注射光度法测定生活用水中氯离子

将流动注射分析技术应用到双光束分光光度法中，对其理论和实验技术进行了研究，采用自行组装的流动注射系统进行了生活用水中氯离子的测定，获得满意结果。     

Integrated Biosensor Systems for Ethanol Analysis

Different integrated systems with a bi-enzymatic biosensor, working with two different methods for ethanol detection—flow injection analysis (FIA) or sequential injection analysis (SIA)—were developed and applied for ethanol extracted from gasohol mixtures, as well as for samples of alcoholic beverages and fermentation medium. A detection range of 0.05–1.5 g ethanol/l, with a correlation coefficient of 0.9909, has been reached when using FIA system, working with only one microreactor packed with immobilized alcohol oxidase and injecting free horseradish peroxidase. When using both enzymes, immobilized separately in two microreactors, the detection ranges obtained varied from 0.001 to 0.066 g ethanol/l, without on-line dilution to 0.010–0.047 g ethanol/l when a 1:7,000 dilution ratio was employed, reaching correlation coefficients of 0.9897 and 0.9992, respectively. For the integrated biosensor SIA system with the stop–flow technique, the linear range was 0.005–0.04 g/l, with a correlation coefficient of 0.9922.     

流动注射分析

本文是《分析试验室》杂志“流动注射分析”专题定期评述的第五篇，评述了国内学者自１９９５年１月至１９９６年１２月期间在国内外发表的有关流动注射分析的论文。内容包括：会议、基础研究与一般性问题、仪器与装置、分光光度检测、原子光谱检测、电化学检测、化学发光及荧光检测等。共引用参考文献２５０篇。     

The impact of flow injection on modern chemical analysis: has it fulfilled our expectations? And where are we going?

Presenting a condensation of the opening lecture of the 12th ICFIA conference, this communication presents a view of the impact that flow injection analysis (FIA) has had on modern analytical chemistry, evaluated both within the academic community and outside it, i.e. in “industry”. The ensuing developments of FIA, encompassing sequential injection analysis (SIA) and bead injection lab-on-valve (BI-LOV), are described and their individual features discussed. Finally, some recent results of the activities from the author’s own research group are briefly mentioned.     

Peroxyoxalate Photoinduced Chemiluminescence Detection of Norfloxacin in Pharmaceutical Products by Flow Injection Analysis

A new method for the determination of norfloxacin by flow injection analysis based on photoinduced chemiluminescence detection is proposed. We have selected the peroxyoxalate (PO) reaction based on the possibility of detecting fluorescent products derived from a photochemically induced decomposition of norfloxacin, observing high signal when the derivative participates in the reaction. A FIA device, with two-injection valves for the introduction of both the PO and the photodecomposed analyte solutions in the flow system, has been used, avoiding the problems arising from the use of organic solvents. The method was applied to the monitoring of norfloxacin in pharmaceuticals.     

Conductometric determination of ammonium by a multisyringe flow injection system applying gas diffusion

A multisyringe flow injection system (MSFIA) coupled to a gas-diffusion cell has been developed for the conductometric determination of ammonium in different water samples. Operation strategies, membrane, reagent concentrations, and flow rates have been studied to optimize the sensitivity of detection and to fit the required working range. The proposed MSFIA system has been compared with former FIA and SIA systems using gas diffusion. The system was applied to the determination of ammonium in water samples of different matrices in order to evaluate its performance. These samples were coastal waters, pond waters, and compost aqueous extracts. Good recoveries of 102?±?13% were obtained and no significant differences with the reference methods were found. The system can be used for a wide concentration range of ammonia, from 0.075 to 360?mg?L^?1, without sample dilution and with a precision better than 2% of RSD. The throughput of the method was 32 injections per hour.     

Stopped-flow injection analysis. The influence of diffusion on dispersion of normal and reverse flow injection

A relationship is derived to enable the comparison of the dispersion heights of normal and reverse flow injection analysis (FIA). A single channel flow system is employed in the absence of a chemical reaction. The stopped-flow injection method is used to probe the influence of molecular diffusion on the overall dispersion of normal and reverse FIA, which appeared to demonstrate fundamentally different diffusion behaviors. Small discrepancies are observed between the dispersion heights, which are enhanced by the stopped-flow period, especially when unmatched matrix ionic compositions of the indicator and counter solutions were involved. For these conditions, the diffusion flux rate is enhanced considerably, displaying a peak, in addition to the transient, for both methods. The influence of diffusion on the dispersion characteristics of normal and reverse FIA is discussed theoretically. Diffusion in the proposed model is postulated to oppose dispersion by convection. The latter initiates concentration gradients in the injection zone and propagates it with flow time over the dispersion zone profile. The diffusion flux then reacts in order to confine the indicator dispersion for normal FIA and to enhance it for reverse FIA. This model is consistent with the experimental results and accounts for most of the phenomena encountered. Probably owing to the influence of secondary flow phenomena, the use of coiled tubes has suppressed the effects of diffusion on the overall dispersion behavior.Part of the experimental work was performed at IMI Institute for Research and Development, Haifa, Israel.     

Examination of the temporal effect in a flow injection analysis system using multi-channel absorbance detection

In addition to the Poiseuille effect, a so-called temporal effect was proposed recently to elucidate the commonly observed tailing peak signals of flow injection analysis (FIA). A multi-channel absorbance detector was used in this study to obtain the FIA peaks on both the spatial and temporal coordinates. The temporal effect was analyzed by comparison of the profiles between the experimental and the corresponding Gaussian peaks, and by comparison of asymmetry factors between the spatial and the temporal peaks. The temporal effect appeared to be the major factor under flow rates ranging from 0.5 to 8 ml min⁻¹. This was despite the presence of a spatially frontal peak observed in the FIA tubing, which was found to result in a tailing peak on the temporal coordinate due to this discussed cause. In addition, the temporal effect became greater as the flow rate increased.     

Increasing the scope and power of flow-injection analysis through chemometric approaches

The objective of this paper is to illustrate how chemometrics can enhance the scope and power of flow injection analysis (FIA) by considering a few simple but representative cases where the ability of chemometrics to improve performance is not readily apparent. In principle, there are two phases when chemometrics can be usefully combined with FIA: first when developing an FIA method and, second, when treating raw data acquired from an FIA detection system. The most obvious application of chemometrics for the FIA practitioner is to use experimental design to replace the obsolete, but too often used one-variable-at-a-time approach when optimising an FIA method. Therefore, methods for screening variables and system optimisation are discussed. Raw data acquired from most FIA systems are first-order data, containing information about the dispersed sample plug. However, the information that is extracted when using FIA for routine purposes is of zero-order: predominantly peak height values. It is shown by a simple example that a chemometric approach in such cases can again provide additional useful information about the sample. First-order spectral data and second-order data more or less require a chemometrics approach for successful analysis, and examples of such applications are briefly discussed.     

Electronic tongues in flow analysis

This review presents the evolution of recent flow-based analytical systems, characterized by the use of arrays of sensors as a detection scheme. For the proper processing of the complex responses generated, the systems require the use of advanced chemometric treatment, in which received the term “electronic tongue”. Applications employing the flow injection analysis (FIA) and sequential injection analysis (SIA) are described. Chronologically, the progresses made by different research groups are shown, emphasizing their final applications in real problem solving.