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.     

Determination of formaldehyde in frozen fish with formaldehyde dehydrogenase using a flow injection system with an incorporated gel-filtration chromatography column

A flow injection analysis (FIA) system for determination of formaldehyde in frozen fish products is described. The system provides a rapid and selective determination of formaldehyde in aqueous fish extracts by the combination of a deproteinization procedure and a stopped-flow enzymatic approach in a FIA system. The FIA system is furnished with a gel-filtration chromatography column for on-line removal of the proteins from the extract before the enzymatic analysis is performed. Compared with the standard methods for determination of formaldehyde in fish products the present method is much faster and less affected by interferences. The limit of detection for the proposed method is 2.5 mg/l of formaldehyde. The sampling frequency is about 10 determinations per hour.     

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.     

平头pH电极-流动注射联用技术快速滴定食醋中醋酸的方法研究

采用一种具有平头结构的pH电极作为流动注射分析(FIA)的检测器,构建了流动注射自动化酸度滴定系统.优化了样品进样量、流速、载液浓度和反应管长度等参数.用NaOH溶液作为载液,在4.639×10-4～0.212 mol·L-1范围内醋酸浓度的对数与FIA峰的峰面积成正比,该方法的相对标准偏差(RSD)小于0.5%.采用...     

New approaches to molecular spectroscopic detection in flow-injection analysis

A state-of-the-art overview of molecular spectroscopy as applied in flow injection analysis (FIA) is presented. It deals chiefly with the most interesting FIA approaches aimed at improving detector performance, innovations in the detection system itself and the coupling of FIA with unusual detectors for this technique. The most salient trends in relation to this association are also commented upon.     

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.     

Development of an automated on-line analysis system using flow injection, ultrasound filtration and CCD detection

The design and construction of an automated on-line analysis system is described with reference to applications in bioprocess control, clinical, and environmental analysis. The new system is built around three main elements: ultrasound filtration, a micro flow injection analysis (FIA) system, and direct readout spectrophotometry. The advantages of three on-line ultrasound filtration devices, developed for clarification of water, human blood and mammalian cell culture samples, are described. The filters avoid off-line centrifugation and do not suffer from the blockage problems associated with conventional filters. The separation efficiency of the ultrasound filters is also discussed. The delivery system is based on a gas driven FIA technique, using helium to avoid bubble formation, with the carrier and reagent flow being controlled by computer switched solenoid valves. Direct readout spectrometers are used, based on charge coupled devices (CCDs) covering the wavelength range 200-900 nm. These detectors provide near instantaneous capture of full spectra, allowing several analytes to be monitored simultaneously, and are much smaller than conventional spectrophotometers. Optical fibres are used to link the light source to the detector via a flow cell in the FIA system. Software to run the entire system was developed using the LabVIEWtrade mark graphical programming environment, enabling rapid development of the control system and user interface. The integration of these components has shown significant improvement in the application of FIA techniques to on-line analysis.     

Chemiluminescence Flow-Injection System for Rapid Detection of Red Tide Phytoplankton

Abstract

A chemiluminescent flow-injection analysis (FIA) system for the detection of the red tide phytoplankton Chattonella antiqua has been developed based on a Cypridina luciferin analog, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1, 2-α]-pyrazin-3-one (MCLA), which strongly emits light at 465 nm in the presence of superoxide. The system consisted of a two reagent feeding stream, a sample injector, a joint for mixing MCLA and sample, a chemiluminescence (CL) reaction cell, a CL detector and a recorder unit. The response time is approximately 1 min for one measurement cycle. The FIA system has an optimum pH of 10.7. The calibration curves for C. antiqua displayed linearity from 2 × 10³ to 2 × 10⁴ cells ml^?1. When applied to the measurement of C. antiqua, the sensitivity obtained using the FIA system is approximately 10 times higher than that of the cytochrome c method. The FIA system is a rapid practical method for the detection of C. antiqua.     

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.     

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.     

Micro-flow injection system for the urinary protein assay

A urinary protein assay has been investigated, employing a micro-flow injection analysis (μFIA) combined with an adsorptive separation of protein from analyte. The adsorptive separation part of protein in the artificial urine with ceramic hydroxyapatite is integrated on the μFIA chip, since the interference of other components coexisting in urine occurs in the conventional FIA system. The typical FI peak can be obtained following the adsorption–elution process of the protein prior to the detection, and the protein concentration in artificial urine can be quantitatively determined.     

Determination of glycol in aircraft ground deicing/anti-icing fluids using flow injection with refractive index detection

A simple method for determining glycol in deicing/anti-icing fluids has been developed. The method uses a single line FIA system with detection based on Schlieren optics. The concentration range was 0-5% glycol and the limit of detection was 0.05%. Samples were preferably pumped at a flow rate of 0.7 ml/min and 100 mul of distilled water was injected (reverse FIA). Detection was accomplished with an 18 mul spectrophotometric flow cell at a wavelength of 410 nm. The conduit connecting the injector and the detector was 10 cm long and had an inner diameter of 0.5 mm. The traditional FIA approach can also be applied, i.e. injection of samples into a carrier of water, but the linear working range is narrower in comparison to the reverse FIA method. Standard addition and near infrared spectroscopy confirmed the validity of the developed method.     

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.     

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。     

Prediction of the behaviour of a single flow-injection manifold

This paper suggests a handy method of obtaining equations to predict the fundamental parameters of an FIA peak--travel time, baseline-to-baseline time, peak height and appearance time of the maximum for a simple configuration--by performing a small number of preliminary experiments in the region in which FIA system usually operates.     

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.     

Determination of aluminum in beverages by automated non-segmented continuous flow analysis with fluorescent detection of the lumogallion complex

A method for the automated determination of aluminum in a variety of beverages is described. The method utilizes lumogallion as a complexing agent in a buffer solution. The system is very similar to flow-injection analysis (FIA), however, the tubing id is larger than that typically used in FIA. Therefore, the system is best described as non-segmented continuous flow analysis using fluorescence spectroscopy detection. The method is extremely simple, requiring virtually no sample preparation and only one reagent. The instrument detection limit for aluminum is 0.012 microgram ml-1 and calibration is linear to 3 micrograms ml-1. Results from a variety of beverage matrices are discussed and compared with the frequently used 8-hydroxyquinolone method utilizing a chloroform extraction and fluorescence spectroscopy detection.     

Potentiometric determination of dialysate urea nitrogen

An enzymatically modified ammonium ion-selective electrode has been applied for the determination of urea in spent dialysate. The biosensor has been used in a simple flow-injection analysis (FIA) system. The system enables one to perform over 25 dialysate urea nitrogen (DUN) determinations per hour. The interferences from other components of posthemodialysis fluid were eliminated by simultaneous measurements with non-modified enzymatically ion-selective electrode. It is possible to use both the sensors in a simplified differential potentiometric system. The results of DUN determination using the biosensor/FIA system and a conventional method of urea determination were comparable. The presented analytical system can potentially find wider biomedical application in the monitoring of hemodialysis progress.     

Flow-injection analysis for hypoxanthine in meat with dissolved oxygen detector and enzyme reactor

A low cost flow-injection analysis (FIA) with a dissolved oxygen (DO) detector and a xanthine oxidase immobilized column for the analysis of hypoxanthine as an index to determine degree of aging in meat was developed for quality control in the food industry. In this system, hypoxanthine is oxidized by an enzyme reaction with xanthine oxidase immobilized on the column to produce xanthine. Then the catalytic reaction between hypoxanthine and DO with xanthine oxidase proceeds with the DO concentration decreasing in the stream of the flow system. Decrease in the DO concentration was monitored by a DO detector located downstream of the flow system. This decrease in DO concentration was proportional to the hypoxanthine concentration. For detecting the decreased DO concentration efficiently a flow-through cell with a polarographic-type DO sensor was specially designed. As a result, a linear working curve was obtained from 3.68 × 10⁻⁵ to 1.84 × 10⁻³ M hypoxanthine concentrations with this FIA system. We applied the present system with a DO detector for the determination of hypoxanthine in meat samples and compared the results with those obtained by the conventional HPLC method. The data obtained with the present FIA method were in fairly good agreement with those obtained by the conventional HPLC method for the meat samples. Correlation factor and regression line between the two methods were 0.998 and Y= 1.51X-32.64 respectively. We concluded that the present FIA system with a DO detector was suitable as a simple, easy to handle and reliable instrument for quality control in the food industry.     

Flow Injection Analysis System Using Magnetic Beads,Screen Printed Electrodes and Magnets

Here is presented a Flow Injection Analysis (FIA) system using a flow cell with an integrated magnet, applied to biotin determination. The mixture of magnetic beads modified with streptavidin (Strep‐MB), biotin and B‐HRP is left 15 minutes under stirring and then a washing step is performed in an automatic way thanks to the external magnets coupled in the FIA system. After the immobilization of the MBs on the surface of the electrode, 3,3′,5,5′‐Tetramethylbenzidine (TMB) is injected. The linear range obtained is between 0.5 to 10 pM of biotin and the sensitivity is 85 nA/pM.