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

The research aims to design a new flow injection system using the two continuous and successive techniques for the determination of cerium quaternary, through the interaction of cerium quaternary with potassium iodide in an acidic medium and the liberation of yellow-colored iodine, which gives a maximum absorption peak at the wavelength is 353 nm. The method includes manufacturing a quadruple valve from cheap materials and choosing the optimal system design with studying the optimal conditions for the system, which include potassium iodide concentration, acid concentration, Pump speed, acid volume, pattern size, reaction profile length, then designing a new sequential injection system and selecting the optimal design for it. The flow injection method yielded compliance with Beer-Lambert law in the range (1-40 mg/L). And a correlation coefficient (R2) of 0.997, and a dilution coefficient equal to 1.33 and 1.32 for concentrations of 10 and 30 mg / L, respectively. The sequential injection method also gave a clear improvement in the height of the apex and an increase in sensitivity.

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.

A Sequential Injection (SI) system was used to analyze the ethanol concentration in fermentation broth. The method is based on the use of immobilized NAD+ dependent alcohol dehydrogenase. A non linear standard curve for ethanol (range 0.25–100 mM) was used to determine the concentration in fermentation broth and the results correlated well with HPLC measurements. The assay time was 140 s, 0.5 μmol of cofactor was used for each determination, and the relative standard deviation was less than 6% when analyzing fermentation samples. The assay system is very stable and makes it possible to reduce the cofactor consumption while keeping the system set up simple.

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

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)

A sequential injection analysis (SIA) system for the spectrophotometric determination of L(+)-lactate using lactate oxidase/peroxidase was developed and applied to wine analysis. It incorporates a dialysis unit between the pump and the selecting valve to provide on-line dilution and interference minimization of the sample matrix. A volume of 100 µL of carrier solution trapped in one channel of the dialysis unit, acts as donor and acceptor solution. With an assay cycle of 262 seconds, the system allows a sample throughput of 14 samples per hour and yields precise results (rsd < 2%). Peroxidase (0.0512 IU) and 0.0384 IU of lactate oxidase promote the conversion of L(+)-lactate in 160 µL of sample, allowing its determination within the 0.25 to 2.5 g/L range. A detection limit of 0.074 g/L was calculated. Results are in good agreement with those obtained with the conventional method (Boehringer UV-Kit).

A reagent-free method based on a photo-induced fluorimetry in a sequential injection system

Sequential injection system in flame atomic absorption spectrometry for the determination of calcium and magnesium in mineral waters

In order to improve the quality control of dehydrated broth, a new automated method was developed to determine total creatinine in dehydrated broths. The sample pretreatment was coupled on‐line with the Flow Injection Analysis (FIA) system for analyte determination by the classical Jaffé reaction, stopped flow methodology, and spectrophotometric detection. The time consumed was reduced from 7 h, which is necessary with the official method, to 25 min. The calibration graph is linear between 0.342–1.368 mg creatinine/100 mL. The relative standard deviation (RSD%) was 1.7%, the sample throughput was 7 h−1, and the detection limit was 0.185 mg creatinine/100 mL. The validation of the proposed method was carried out with real samples. The obtained results were compared with those obtained from the Association of Official Analytical Chemists (AOAC) reference method.

Evaluation of natural computation techniques in the modelling and optimization of a sequential injection flow system for colorimetric iron(III) determination

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

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 system with higher dimensional electrochemical sensor signals: Part 1. Voltammetric e-tongue for the determination of oxidizable compounds

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

This paper reports an automated analytical method for rapid and simultaneous determination of plutonium isotopes (239Pu and 240Pu) and neptunium (237Np) in environmental samples. An extraction chromatographic column packed with TrisKem TEVA® resin was incorporated in a sequential injection (SI) system for the isolation of plutonium and neptunium from matrix elements and interfering nuclides. Valence adjustment is a crucial step to ensure the same chemical behavior of plutonium and neptunium onto the TEVA column and consequently to accomplish their simultaneous separation and detection. Distinct procedures were investigated and compared for the adjustment of oxidation states of plutonium and neptunium to Pu(IV) and Np(IV), respectively. A two-step protocol using sulfite and concentrated nitric acid as redox reagents was proven to be the most effective method. The analytical results for both plutonium and neptunium in three reference materials were in agreement with the recommended or literature values at the 0.05 significance level. The developed method is suitable for the analysis of up to 10 g of soil and 20 g of seaweed samples. The extraction chromatographic separation within the SI system for a single sample takes less than 1.5 h. As compared to batchwise procedures, the developed method significantly improves the analysis efficiency, reduces the labor intensity and expedites the simultaneous determination of plutonium and neptunium as demanded in emergency actions.