Determination of cerium (IV) by continuous flow injection and sequential flow injection methods

Two approaches for performing competitive binding immunoassays by HPLC and other flow-based systems are the simultaneous and sequential injection methods. Both these techniques make use of a column with a limited amount of antibody, onto which is injected a sample and a fixed amount of a labeled analyte analog. An indirect measure of the unlabeled analyte in the sample is then obtained by looking at the amount of analog in either the nonretained or retained peaks. In the simultaneous injection mode, the sample and labeled analog are applied at the same time to the column, while in the sequential mode the sample is injected first, followed by the analog. This results in a difference in the analytical characteristics of these two approaches. This study used chromatographic theory and previous data obtained for injections of human serum albumin (HSA) onto an anti-HSA antibody column to compare the response, detection limits, range, and sensitivity of these methods. Under equivalent conditions, it was found that the sequential method always provided the best lower limit of detection and sensitivity. However, the simultaneous mode had a broader dynamic range and higher upper limit of detection. From these observations, several guidelines were developed regarding the use and selection of such assays for new applications.

Pyoverdin, a natural fluorescent pigment biosynthesized by Pseudomonas fluorescence, was entrapped in sol–gel glass and used as a reactive solid phase for the determination of trace amounts of FeIII. No leaching or bleaching of the trapped reagent was observed. The fluorescent siderophore was more stable in sol–gel glass than on controlled-pore glass. Iron(III) was determined by continuous flow and flow injection (FI) methods. Both methods provided a fast response. The detection limits were 3 ng ml–1(relative standard deviation, 3.0% for 150 ng ml–1 of FeIII) and 20 ng ml–1(relative standard deviation, 4.5% for 500 ng ml–1 of FeIII) for the continuous and FI (sample injection 1 ml) systems, respectively. The selective sensor was successfully used to determine iron in tap waters (continuous system) and human serum (FI system).

Determination of mercury(II) at trace levels by gas-diffusion flow injection analysis with amperometric detection

Determination of iron(III) in pharmaceutical samples using dialysis in a sequential injection analysis system

A flow-injection (FI) method was developed for the spectrophotometric determination of cadmium in a hydrometallurgical zinc refining process stream using 1-(4-nitrophenyl)-3-(4-phenylazophenyl)triazene (Cadion) as the chromogenic reagent. The sample solution was injected into a carrier containing potassium iodide. The sample was then passed through an anion-exchange mini-column on which the analyte was concentrated as a cadmium–iodo complex. In order to extend the detectable range of cadmium, a multiple sample injection method, in which the sample solution was repeatedly injected into the carrier at regular intervals of 30 s, was applied. Cadmium on the column was eluted with 1 mol l–1 nitric acid and merged with a stream of a mixture of masking agent (trisodium citrate–potassium sodium tartrate–potassium hydroxide) and Cadion. Finally, the absorbance of the cadmium–Cadion complex was measured at 480 nm. The proposed FI was fully controlled by a personal computer. The proposed system permitted throughputs of 6 samples h–1 for single injection, and 2 samples h–1 for single injection, and 2 samples h–1 for multiple sample injection (50 injections). The reproducibility was satisfactory with a relative standard deviation of less than 5.0%(0.14 µg ml–1 Cd level, n= 5) for the single injection method and 10%(2.0 ng ml–1 Cd level, n= 5) for the multiple sample injection method (50 injections). The detection limits were 0.028 µg ml–1 of cadmium for the single injection method and 0.83 ng ml–1 of cadmium for the multiple sample injection method (50 injections). The absolute amount of cadmium detectable, defined as the analytical signal equal to twice the uncertainty in the background, was 10 ng.

This paper introduces a novel methodology for downscaling reagent based assays to micro- and submicroliter level. It is shown that sample handling in the sequential injection mode, which employs forward, reversed and stopped flow, can be programmed to accommodate a wide variety of assays within the same microfluidic device. Solution metering, mixing, dilution, incubation and monitoring can be executed in any desired sequence in a system of channels, integrated with a multipurpose flow cell. The channel system and flow cell are fabricated as a monolithic structure mounted atop a conventional multiposition valve. In addition to compactness, the advantage of this ‘lab-on-valve’ system is the permanent rigid position of the sample processing channels that ensures repeatability of microfluidic manipulations, controlled by conventional sized peripherals. With the exception of the integrated microconduit system, that has been designed and mesofabricated by computer aided design (CAD) technology, all peripherals (sequential injection system, fiber optic UV/VIS spectrophotometer-fluorometer) are conventional sized and commercially available components. This provides proven robustness and reliability of operation, and makes the microfluidic system compatible with real life samples and peripheral instruments. The system has been characterized by dye injection, to provide guidelines for method development. Its versatility is documented by a phosphate assay, enzymatic activity assay of protease and by a bioligand interaction assay of immunoglobulin G (IgG) based on its interaction with protein G immobilized on Sepharose beads.

Sequential flow injection spectrophotometric determination of nitrite and nitrate in various samples

Evaluation of a novel PTFE material for use as a means for separation and preconcentration of trace levels of metal ions in sequential injection (SI) and sequential injection lab-on-valve (SI-LOV) systemsDetermination of cadmium(II) with detection by electrothermal atomic absorption spectrometry (ETAAS)

Enhancement of the chemiluminescence of penicillamine and ephedrine after derivatization with aldehydes using tris(bipyridyl)ruthenium(II) peroxydisulfate system and its analytical application

R. T. Echols, R. R. James and J. H. Aldstadt, Analyst, 1997, 122, 315 DOI: 10.1039/A605662H

It was found that oxides of manganese (MnOx), bismuth (ВiOx), gold (AuOx), and ВiOx–MnOx and MnOx–AuOx binary systems electrodeposited on the surface of planar carbon electrodes (SPE) exhibited catalytic activity during electrooxidation of thiamine, riboflavin, pyridoxine and cyanocobalamin in acidic media. Immobilization of the binary systems on the surface of the SPE working electrode allowed to achieve a joint selective voltammetric determination of two-component systems of the vitamins considered: riboflavin and pyridoxine on SPE with BiOx–MnOx (ВiOx–MnOx–SPE) and MnOx–AuOx (MnOx–AuOx–SPE); and riboflavin and thiamine or riboflavin and cyanocobalamin on MnOx–AuOx–SPE. The calibration dependences obtained for the considered vitamins using voltammetry on BiOx–MnOx–SPE and MnOx–AuOx–SPE electrodes were observed in the range from 1×10–6 to 1×10–3 M. Detection limit of thiamine, pyridoxine and cyanocobalamin was decreased by an order of magnitude compare to static conditions in a sequential injection system (SI-system). To implement two- and three-component analysis of biologically active additives (BAA) and drugs in the SI-system, the surface of the working electrode modified with MnOx–AuOx binary system was covered with poly-2-vinylpyridine (PVP) or Nafion (Nf) polymer films. SPE with two working electrodes (DSPE) modifies with MnOx–AuOx were used in the two-component analysis of BAA samples. PVP film was deposited on the electrode for thiamine determination and Nf film was deposited on the electrode for pyridoxine determination. Combination of SPE and DSPE with polymer composites containing MnOx–AuOx binary system and PVP or Nf in a two-detector SI-system made it possible to implement a three-component analysis of drugs containing thiamine, pyridoxine and cyanocobalamin. Excipients present in them did not interfere with the results of the determination. Application of the proposed SI-system scheme increased selectivity, speed and productivity of the analysis to 540 determinations per hour.

Sequential injection flow system with improved sample throughput: determination of glycerol and ethanol in wines

Automated magnetic sorbent extraction based on octadecylsilane functionalized maghemite magnetic particles in a sequential injection system coupled with electrothermal atomic absorption spectrometry for metal determination

Determination of trace elements in water samples by ultrasonic nebulization inductively coupled plasma mass spectrometry after cloud point extraction

Determination of cobalt in zinc electrolyte by an automated flow-injection system