This review introduces a number of flow injection analysis based enzymic methods and biosensors for the determination of various analytes with interest in food, environmental and cosmetics analysis. Particular attention has been paid on the selectivity of the reviewed works as well as on their practicality in terms of flow injection manifold assembly, the fabrication of the enzyme electrodes and the performance of the measurements. A flexible and easy way to achieve upgrading of a typical flow injection manifold to a fully automated one, by means of resident software, is presented. Enzymatic methods based on packed-bed reactors bearing the immobilized enzyme(s) are discussed. The reviewed biosensors are based on a multi-membrane architecture consisted: i) of a cellulose acetate membrane in order to keep away possible interferants from the electrode surface, ii) the enzymic membrane and iii) an outer one, which protects immobilized enzyme(s) from leaching and microbial attack. Examples of various enzyme electrodes, published in the literature during the last decade, along with some flow amperometric cells are also presented.
Online separation and concentration promise sensitive and reliable analyses in FIA. In addition, they contribute to the speciation by FIA. This tutorial review is intended to describe online solvent- and solid-extractions as typical and practical separation/concentration techniques in FIA. The principle, feature, instrumentation, application and recent trend of the techniques are discussed.
Sequential injection analysis technique was employed as a successful tool for titrimetric determination of paracetamol in drug formulation. The potential aspect of paracetamol to reduce the absorbance of potassium permanganate in sulfuric acid media was applied to develop an ideal spectrophotometric data. The super modified simplex computer program was operated to optimize the main reaction parameters such as sulfuric acid and potassium permanganate concentrations and the (3f) factorial design was employed for studying their interaction effects. This method was found to be optimum at 1.79×10-3 mol dm-3 potassium permanganate and 0.071 mol dm-3 sulfuric acid concentrations for the detection limit between 50 to 350 ppm. The results obtained showed an accurate outcome when statistically compared with the BP standard method. The method reveals no interferences from most of the added excipients in drug formulation.
In this work is proposed a very simple flow injection method for the analysis of acetylsalicylic acid (asa) in pharmaceutical preparations. The method is based on the asa alkaline hydrolysis forming a solution containing acetate and salicylate. This solution is mixed with a sulfuric acid solution. The acetic acid formed permeates through a PTFE membrane to a deionized water stream presenting less than 20 micro Siemens of conductance. The change in conductance was registered in a chart recorder. Six pharmaceutical preparations purchased in the local market were analyzed. The obtained results were compared with those obtained with the Pharmacopoeia titrimetric method. The statistical t-Student test was applied to compare the results obtained with the two independent methods. In all cases complete agreement was observed, in a confidence level of 95% (α=0.05). Considering six samples analyzed using the proposed method and three determinations for each sample, the observed mean RSD, is 1.1 %. The limit of detection is about 2×10-4 mol l-1 (3×SD) and the analytical frequency is 60 determinations per hour.
Between-method carryover due to reagent replacement in flow systems devoted to multiparametric determinations is critically discussed. For this task, a model system involving the spectrophotometric procedure for iron speciation in natural waters based on the known reaction of Fe(II) with 1,10-phenanthroline was initially designed. Furthermore, other systems for different bi-parametric assays were also highlighted. Potentialities and limitations of the different strategies for compensating and/or reducing between-method carryover are discussed, and guidelines for laboratory management are withdrawn.
A sequential Injection (SI) method for the determination of Bromazepam (BRZ) is described. The proposed method is based on the enhancement of BRZ fluorescence in the presence of a non-ionic surfactant Tergitol XH and lactose. The fluorescence was monitored at 423 nm with excitation at 340 nm. The optimum concentration of surfactants and lactose were determined using a univariate approach. With the optimum conditions described, linear calibration curves were obtained from 25 ppm to 200 ppm. The method was successfully applied for the determination of BRZ in pharmaceutical formulations using the standard addition technique.
An Amperometric flow injection system to measure the density of attached animal cells in hydroxyapatite-pulp composite fiber (HAPC) sheets was developed. 2,3,5-Trimethyl-1,4-benzoquinone (BQ) was injected into the HAPC sheet module containing animal cells as a mediator. 29375-Trimethyl-l,4-hydroquinone, which was produced by the reduction process of animal cells, was monitored amperometrically with a glassy carbon electrode. The carrier solution used was Dulbecco's phosphate buffered saline. A good linear relationship between the peak current and attached cell density was obtained in a range of 8.3×105 - 6.1×106 cells/sheet. The propose method can be applied for the measurement of cell density in a range of 8.3×105 - 1.6×107 cellslsheet. The peak current remained steady for 10 successive injections of 2,3,5-trimethyl-1,4-BQ at a concentration of 10 pM. Cytotoxicity due to 2,3,5-trimethyl-1,4-BQ was hardly observed at a concentration of less than 20 pM. This analytical system can be used for monitoring the cell density in bioreactors during the period in which the cells proliferate in the logarithmic phase.
A simple and rapid method for the determination of formaldehyde (HCHO) in air was developed by using a portable flow injection analysis (FIA) system installed with a detector consisting of a light emitting diode (LED) as a light source, and a flow cell and with a heating system. The method was used for on-site measurement by coupling with a simple batchwise absorption collection method. HCHO in air was collected quantitatively on-site in a 50-ml syringe (volume: 71.92±0.43 ml) containing 3 ml of purified water as an absorbing solution, which was subsequently introduced into the carrier stream of the FIA system. The amounts of HCHO in the absorbing solution were measured at 450 nm after reaction with a mixed reagent of acetylacetone and ammonium acetate at pH 6.0 or with a fluoral P solution of 0.4 M phosphate buffer (pH 6.0). A calibration graph with standard HCHO aqueous solutions could be adopted for the determination of formaldehyde in air. The relative standard deviation (RSD) was 0.63% for 1×10-5 M (n = 12) and with the limit of detection (LOD) was 2.7×10-8 M (0.8 ppb) in aqueous solution (SN =3), which corresponds to 35 pptv of HCHO in air. The proposed method was successfully applied to air samples.
The in vivo monitoring of the concentration changes of biomolecules at a variety of sites of the living systems including blood stream, subcutaneous tissue, muscle, internal organs, and brain, has been desired for the pharmacological, clinical, and biological studies. The most general approach to achieve such goals was the use of implanted biosensors, but it was limited because of the variations in sensitivity during the prolonged in vivo monitoring. Recently, microdialysis has been used as a sampling technique for in vivo analysis. This article reviews novel flow-injection biosensor systems which make possible on-line monitoring of glucose metabolism and pharmacological behavior of neurotransmitters in the extracellular space of brain. This approach was developed by coupling microdialysate sampling to the biosensor system using a flow-injection interface. The advances in these researches are reviewed with the results obtained in our recent works.