Automatic Flow Injection System Research Articles

Analysis of pesticides based on immobilized housefly head acetylcholinesterase reactor with choline oxidase and horseradish peroxidase carbon paste electrode

AbstractAn automatic flow injection system (FIA) using the acetylcholinesterase (AChE) reactor connected with the choline oxidase (ChOx) and horseradish peroxidase (HRP) carbon paste electrode for organophosphorous (ORPs) and carbamate pesticides determination is exploited. The ORPs are measured based on the inhibition of AChE. Two different sources of AChE from eel and housefly head are studied, respectively. The detection limit for paraoxon (10 ppb) and carbofuran (23 ppb) is found in the housefly head AChE. The AChE from housefly head shows 16 times higher sensitivity than the enzyme from eel for paraoxon. The linear range of the housefly head AChE biosensor is 8–100 ppb. The throughput of five‐sample hour−1 is obtained with a good reproducibility. The fruit juice and river water samples are studied and show the feasibility for further applications.

Small Mass-Change Detectable Quartz Crystal Microbalance and Its Application to Enzymatic One-Base Elongation on DNA

A highly sensitive 27 MHz quartz crystal microbalance instrument with an automatic flow injection system was developed to obtain realistic minimal frequency noise (±0.05 Hz) and to obtain a stable signal baseline (±1 Hz/h) by controlling the temperature of each part in the quartz crystal microbalance (QCM) system using three Peltier devices with a resolution of ±0.001 °C and by optimizing the flow system to prevent fluctuation of the internal pressure of the QCM. The improved QCM with an automatic flow injection system enabled detection of small mass changes such as binding of biotin to a streptavidin-immobilized QCM with a high signal-to-noise ratio. We also applied this device to enzyme reactions of one-base elongation by DNA polymerase (Klenow fragment, KF). We immobilized dsDNAs including the protruding end of dA, dG, dT, or dC on the QCM electrode and ran complementary dNTP monomers with KF into the QCM flow cell. We could directly detect the enzymatic one-base elongation of DNA as a small mass increase, and we found the difference in the reaction rate for each monomer.

Application of Flow Injection Gradient Titration Based on the Standard Addition and Dilution Procedure to the Determination of Total Acidity in Vinegars and Soft Drinks

The proposed approach relies on successive dilution of a solution containing a sample with standard addition and on titration of the solutions obtained until receiving a signal lower than the signal measured for the sample alone. Equations are derived for subsequent dilution factors for the automatic flow injection system applied. The overall calibration strategy including the possibility of prediction of the number of required standard solutions and of positioning the sample signal within the calibration range is presented. The method has been tested on the spectrophotometric determination of hydrochloric acid at two concentration levels (0.193 and 1.21 mol L(-1)) with sodium hydroxide as titrant. The results of accuracy better than |3.9|% (RE) and repeatability better than 1.3% (RSD) were obtained. The method has been applied to the determination of total acidity in vinegars and soft drinks. The average time necessary to analyze one sample is about 10 min.

Automatic flow-injection system for the determination of heavy metals in sewage sludge by microwave digestion and detection by inductively coupled plasma-atomic emission spectrometry (MW-ICP/AES).

Results are shown obtained in the optimization of an automatic flow injection system that combines microwave digestion with atomic spectrometric detection (FAAS, ICP/AES) for the determination of heavy metals in sewage sludge. Digestion is performed by preparing a suspension of the sample in 1.5 mol/l HNO(3) and making it flow through a PTFE capillary tube placed inside a conventional microwave oven. The effects of the length and inner diameter of the capillary tube, as well as that of the pumping rate, have been studied in order to find the experimental conditions that allow a quantitative elemental recovery in the shortest period of time possible. The optimization study was carried out on a certified sample (BCR No. 146), and the elements determined were Zn, Cu, Pb, Cd, Ni and Cr. The experimental data (percent recovery vs. digestion time) have been fitted to a mathematical model in order to quantify the influence of each of the variables studied. The optimized procedure (MW-ICP/AES) has been applied to one ordinary and one certified sewage sludge sample. In comparison with the conventional methods of sewage sludge analysis, the one proposed is less time consuming, while being equally precise and accurate.

Determination of calcium, magnesium, sodium and potassium in wines by FIA using an automatic zone sampling system

In this paper, an automatic flow injection system based on the zone sampling technique for the determination of calcium and magnesium in wines by atomic absorption spectrometry, and sodium and potassium by flame photometry, is described. A reproducible cleavage of a portion of the injected sample plug was achieved by using two computer-controlled rotatory valves. The developed methodology yielded up to a 2000-fold dilution, without a significant decrease in the sampling rate, which was never lower than 90 determinations per h for any of the species analyzed. The quality of the results obtained with the automatic system for several types of wines was evaluated by comparison with those obtained with the reference methods. A relative standard deviation of less than 3% was achieved for all the samples ( n = 15) and species analyzed.

Polypyrrole, a new possibility for covalent binding of oxidoreductases to electrode surfaces as a base for stable biosensors

Preparation and functionalization of conducting polypyrrole films on different materials provide surfaces suitable to bind enzymes covalently after carbodiimide activation. The enzyme electrodes have been tested in comparison to electrodes obtained by binding of oxidases to graphite surfaces. Covalent immobilization of the glucose oxidase directly to the functionalized polypyrrole surface led to biosensors with a short response time, reaching a steady-state current within 30 s in stationary measurements and about 10 s in an automatic flow-injection system. The enzyme electrodes show good stability using oxygen as an electron acceptor, and more than 700 glucose measurements are possible with the new polypyrrole-glucose oxidase electrodes in a flow system.

Determination of free cyanide in mineral leachates

Cyanide leaching is a common process by which metals, e.g., silver and gold, can be extracted from ores and related materials. This paper describes an automatic flow injection system for the determination of free cyanide in samples from leaching processes.The sample is injected into a carrier stream, which is merged with a flowing reagent stream. The reagent stream contains sodium hydroxide together with a trace of cyanide and these optimise the solution composition for detection by a cyanide ion-selective electrode. A working range of 10–1 000 p.p.m. is covered with a sample rate of 120 h–1. Sample recoveries compared excellently with a titrimetric procedure and a short-term repeatability study on a sample gave a mean value of 306.5 ± 7.4 p.p.m. at the 95% confidence level. The method selectivity, with particular reference to metal-cyanide complexes, is also discussed. The technique is applicable to process control as well as process development.

Fully automatic flow injection system for the determination of uranium at trace levels in ore leachates

An automatic flow injection system is described for the determination of uranium in ore leachates. Following injection from an autosampler, the leachate is extracted with a solution of tributyl phosphate in heptane, which removes uranium, and the organic phase is separated. The extract is reacted with an ethanolic solution of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (BrPADAP) and benzyldimethyltetradecylammonium chloride (zephiramine) and the resulting ternary complex with U(VI) is measured spectrophotometrically at 579 nm. The lower limit of determination is 0.1 p.p.m. of uranium and up to 50 samples per hour can be analysed. In terms of speed and sensitivity this improves significantly on published procedures using segmented flow systems. The technique is ideal for process control and can be applied to the analysis of ores following mineralisation.