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.     

On the mathematical model of flow injection analysis-II. The second order chemical reaction in a straight tube

The mathematical model of flow injection analysis (FIA) for fast second-order chemical reaction in a straight tube is presented. The sample and reagent are initially premixed and the analytical solution for the detection output, i.e. the integral of the product of reaction concentration over the tube cross-section is given. The optimization of FIA is discussed. It is proposed to put the detector in the real FIA systems immediately after the point where the sample and reagent are satisfactorily mixed.     

Principles and analytical applications of acousto-optic tunable filters, an overview

Advantages of acousto-optic tunable filters have been exploited to develop novel analytical instruments which are not feasible otherwise. The instrumentation development and unique features of such AOTF based instruments including the multidimensional fluorimeter, the multiwavelength thermal lens spectrometer, the near-infrared spectrometer based on erbium doped fiber amplifier (EDFA), and detectors for high performance liquid chromatography (HPLC) and flow injection analysis (FIA), will be described.     

Flow-injection systems for determination of trace manganese in various salts by catalytic photometric detection

Two flow-injection analysis (FIA) systems for the determination of trace manganese in salts are presented using highly sensitive catalytic detection based on the oxidation of 3,4-dihydroxybenzoic acid by hydrogen peroxide. Two different approaches, the use of a large sample volume injection in a usual FIA mode (system A) and on-line coupling of a cation-exchange separation column with detection in a continuous flow system (system B), have proved very effective for eliminating the blank peak problem and thus affording direct injection of a sample solution containing a large concentration of salt. The limits of determinations are 0.04 ppm and 0.01 ppm for systems A and B respectively, when a 5 g sample is used for preparing the 100 ml sample solution. The proposed FIA systems were satisfactorily applied to the determination of manganese at 0.03-1.59 ppm in solar salts (salts made by exposing brine to the sun) with good precision.     

Determination of cyanide by a flow injection analysis-atomic absorption spectrometric method

A new flow injection analysis (FIA) procedure is proposed for the indirect atomic absorption spectrometric determination of cyanide. The FIA manifold is based on the insertion of the sample into a distilled water carrier, then the sample flows through a solid-phase reactor filled with silver iodide entrapped in polymeric resin beads. The calibration graph is linear over the range 0.2-6.0 mg l-1 of cyanide (correlation coefficient 0.9974), the detection limit is 0.1 mg l-1, the sample throughput is 193 h-1 and the RSD is 0.8%. The method is simple, quick and more selective than other published FIA procedures. The reproducibility obtained by using different solid-phase reactors and solutions is in the range 2.2-3.1% (RSD). The method was applied to the determination of cyanide in commercial samples such as pharmaceutical formulations and industrial electrolytic baths.     

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。     

流动注射分析中试样分散的对流-扩散理论

用两种方法求解适合于单一平直管道且无化学反应的流动注射分析(FIA)体系的对流-扩散方程,得到了描述塞状进样在管道中分散后的浓度分布公式,从而得到F曲线。讨论了反应管和采样管的内径和长度、流速和扩散系数对峰形和分散度的影响;采用数值法解出半峰宽与扩散系数的关系,提出了两种测定扩散系数的方法,为FIA体系的设计和指示物质、操作条件的选择提供了理论依据。     

Electroanalytical Behaviour of a Nanoarray Self-Assembled Thiocholesterol Gold Electrode

Thiocholesterol forms a self-assembled monolayer (SAM) on polycrystalline gold, offering a defect-rich hydrophobic surface. This SAM gold electrode has been exploited in batch and flow injection analysis (FIA) as it allows selective detection of hydrophobic analytes such as phenothiazines in presence of potentially interfering species such as ascorbic acid. Several phenothiazines have been investigated. Quantification has been achieved in FIA, in a broad linear concentration range: 0.5–100?μM. The stability of the modified electrode allows more than 500 sample injections in FIA.     

Alcohol Electrodes in Beverage Measurements

Abstract

An alcohol electrode which had been optimized¹ to give an extended linear response to alcohol, eliminate the classical electrochemical interferences of hydrogen peroxide-based electrodes and be pH independent, was used to measure the alcohol concentration in beverage samples both in batch and FIA (wall jet) mode. The results obtained were compared to a spectrophotometric measurement used with a Sigma kit. It was found that the batch measurements were more accurate than the kit and FIA, although very good precision could be obtained with FIA. The method is rapid, easy to perform and requires no sample preparation.     

Development of a flow-injection analysis (FIA) enzyme sensor for fructosyl amine monitoring

An enzyme-sensor system with flow-injection analysis (FIA) has been developed for the detection of fructosyl amine compounds; the sensor utilizes fructosyl amine oxidase isolated from the marine yeast Pichia sp. N1-1 strain. With this FIA system 0.2 to 10 mmol L(-1) fructosyl valine can be determined. The sensor is approximately five times more sensitive to fructosyl valine, a model compound for glycated hemoglobin HbA1c, than to N(epsilon)-fructosyl lysine, a model compound for glycated albumin. This FIA system can also be used to detect fructosyl dipeptides. The operational stability of the sensor enabled more than 120 consecutive sample injections over a period of approximately 20 h.     

Flow Injection Zymography - A Novel Procedure For the On-Line Detection of Enzyme Activity

Abstract

This paper describes a new method - Flow Injection Zymography - for the detection of enzyme activity during purification procedures using flow injection analysis (FIA). High sampling frequency (3 samples per minute), small sample volume requirement and a wide range of linearity (up to 70 IU) of enzyme activity was achieved. Reagent costs were minimized using the merging zones mode. the zone sampling technique for sample dilution was successfully incorporated into this system to maintain a reliable signal/response ratio. Most importantly, this new FIA method allowed on the spot identification of the active fractions.     

Fluorimetric determination of fluoride in a flow assembly integrated on-line to an open/closed FIA system to remove interference by solid phase extraction

A simple flow injection fluorimetric method for fluoride determination is proposed. The method is based on the enhanced fluorescence of quercitin-Zr(IV) complex when fluoride ion is present in the sample. An open/closed FIA manifold with a mini-column of Dowex 50W X8 resin was used to remove the most important interference (aluminum). The two FIA assemblies were integrated on-line to automate the pretreatment of the water sample and fluoride determination. The calibration graph was linear over the range 0.1-3.0 mug ml(-1) of fluoride with a correlation coefficient of 0.999 and LOD 0.06 mug ml(-1). The relative standard deviation was 2.5% and the sample throughput was 52 h(-1) without pretreatment and 10 h(-1) with pretreatment of the sample. The method was applied to the determination of fluoride in water samples.     

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.     

土壤速效磷的流动注射光度分析

磷作为作物生长发育必需的营养元素 ,历来被作为土壤肥力水平高低的标志之一。发达国家几乎每年都对土壤的养料状况进行测定 ,根据测定值及土壤与气候条件制订施肥建议。而土壤中速效磷的测定通常采用ＮａＨＣＯ3提取 ,磷钼蓝法和磷钼蓝萃取分光光度法[1 ] 测定。也有采用阴离子交换树脂提取法和同位素交换法[2 ] 。同位素交换法不适于测定高固磷土壤 ,分光光度法手工操作 ,耗时长 ,也不能实现自动分析。本文采用乙基紫 钼酸铵 ＯＰ络合显色的反应体系[5,6] ,流动注射分析技术 ,确立了土壤中速效磷的快速自动分析方法。用于实际样品分析 ,结…     

Flow injection determination of ethanol in whole blood using immobilized enzymes

Enzymatic methods for the determination of ethanol in whole blood are proposed. They use different types of detection and flow injection analysis (FIA) modes: fluorometric detection (use of normal FIA and stopped-flow/FIA); amperometric detection by monitoring of NADH (use of normal amperometric and pulse mode) and with the aid of a coupled enzymatic reaction (2,6-dichlorophenolindophenol/diaphorase). Determination ranges between 0.1 and 30.0 μg/ml are obtained (which in all cases comprise the legal range of ethanol in blood), with good precision and sampling frequency. The sensitivity of the methods can be manipulated by changing the injected sample volume or the pH.     

Design of a flow injection method for chlorophyll determination in in vitro plants

A flow injection (FIA) method was designed for the determination of chlorophylls a and b in small in vitro Dieffenbachia maculata “Sublime” plants. In the first step, the pigments from spinach leaves were separated, purified by solvent extraction and freeze–dried, to obtain standards for the FIA optimization. The sample extraction procedure was optimized. Four solvents were tested: diethyl ether, methanol, acetone and ethanol. The ethanol 96% was the optimal solvent for FIA purposes. It allows to the efficient extraction of the pigments and water can be used as carrier. The best FIA conditions found for the quasi-simultaneous quantification of chlorophylls a and b were a flow rate of 10.84 mL min⁻¹, a sample injection volume of 1.45 mL and a reactor length of 63 cm. The detection was performed with the automatic wavelength scanning Cintra 10e spectrometer, at 649 and 665 nm. The results obtained by the FIA method were compared to those obtained by the Arnon method. A deviation less than 5% was found between results for both methods. The concentration (mg g⁻¹) of chlorophylls a and b during three periods of the plants (in vitro, acclimatization, and adult) was determined to evaluate the whole in vitro procedure. It was found an increment of both pigment concentrations since the in vitro step till the adult stage, while the chlorophylls a to b ratio decreases. The designed method is suitable especially for the determination of the pigments at low concentrations in small samples with appropriate analytical quality.     

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.     

Adaptation of a commercial ion selective fluoride electrode to a tubular configuration for analysis by flow methodologies

The determination of fluoride ions in water samples is accomplished by using a tubular flow through detector constructed by drilling a channel through a commercially available LaF(3) crystal electrode in such a way that the original contacts of the non-modified unit are maintained. Its performance when incorporated in both FIA and SIA systems was evaluated and the results show that the tubular unit retains the characteristics of the non-modified electrode. In SIA conditions an extended linear range of response and lower detection limit were achieved when compared with the electrode performance in FIA conditions. These aspects together with the additional advantage of low sample and reagent consumptions in SIA when compared to FIA, makes the incorporation of the proposed tubular ISE in a SIA system the preferred approach for on line determination and monitoring of fluoride content in natural water samples.     

On-line sample preparation and determination of phenols with a Flow-Analysis method

Summary A Flow-Analysis system has been developed to automate the phenol determination according to the German standard method DIN 38409-H16-2. The automation leads to a significant acceleration of the procedure. One analysis only lasts 3 min while the complete manual determination requires 3 h. Also the sample, solvent and reagent volumes are reduced to a tenth of the volumes demanded by the standard method. The described phenol determination is based on the integration of an airsegmented (Airsegmented-Flow-Analysis SFA) part in a Flow-Injection-Analysis (FIA) system. The main steps of the analytical procedure are: Reproducible inserting of the sample in a carrierstream, sample pretreatment and sample measuring. In the first step the sample is injected into the carrierstream. It transports the sample in the reactioncoil and than through the distillation unit. The steam distillation represents the sample preparation step; therefore an airsegmented stream is necessary. Afterwards the different phases (liquid and gas) were singled again and the distilled solution is fed into the FIA manifold. The determination itself takes place inside the FIA system. The limit of determination amounts to 0.01 mg l^–1 with a standard deviation of 1.5%. Different waste, surface and drinking water samples have been analyzed without any problems. The results correspond very well to those obtained by manual procedure.     

Flow injection analysis for residual chlorine using Pb(II) ion-selective electrode detector

A simple flow injection analysis (FIA) system for residual chlorine in tap water has been developed by using a Pb(II) ion-selective electrode (ISE) detector. The method is based on a specific response of the Pb(II)-ISE to residual chlorine. The FIA system consists of a millivolt meter, a peristaltic pump, a Pb(II)-ISE detector and a recorder. A linear working curve between peak height and concentration of residual chlorine was obtained from 0.1 to 1 mg l(-1) for the developed FIA system. The relative standard deviation for repeated injections of a 0.2 mg l(-1) residual chlorine sample was 2%. The regression line and its correlation factor between the conventional o-tolidine colorimetric method and the present method were Y=0.75X+0.17 and 0.967, respectively, for this determination.