Down scaling for chemical analysis with flow-based techniques with the emphasis on sequential injection systems is reviewed. Sequential Injection (SI) systems with Lab-on-Valve (LOV) offer various advantages. SI with Lab-at-Valve (LAV) approach serves as an alternative cost effective means for automation and miniaturization in chemical analysis. Development of the techniques and their features are discussed.

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The new approach to automate stationary techniques to analyze gas using a stepwise injection analysis (SWIA) is revealed and determination of hydrogen sulfide in natural gas using SWIA is described. The determination is based on absorption of hydrogen sulfide into open to the air reaction tube with 2% zinc acetate solution, stepwise injection of the reagents to the reaction tube to form a methylene blue and subsequent measurement of the downstream colored product at 670 nm. The open to the air reaction tube is a part of hydraulic system and has PTFE granules to increase a surface area during the gas sample bubbling. Nitrogen was purged to the reaction tube for enhanced mixing. All experimental manipulations were controlled by software. The absorbing solution has an absorption efficiency of >98% at a sampling flow rate of 0.3 l/min. This method provides a linear working range of 0.5 to 20 mg/m³ with a relative standard deviation of 2.5 % (n=10) at the 5 mg/m³ level for 3 liters of gas sample and concentration time of 10 min. The determination limit of 0.1 mg/m³ was achieved using 3 liters of gas sample and time of one cycle of 18.5 min.

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An inexpensive FI-manifold and a minicolumn packed with cation exchanger resin with spectrophotometric detection are described for the determination of sulphate ions. It is based on the competitive reaction of SO₄^2- and methythymol blue (MTB) with barium(II) in aqueous solution. Measurements were made at 610 nm. Conditions for the quantitation of sulphate ions were optimized using univariate and simplex methods. The cation exchange minicolumn was used to overcome some possible cationic inferences. Linear calibration graphs over the range of 5-25 mg/l SO₄^2- were established with the regression equation (n=5) Y=2.3172X-3.6798 (r=0.9963). The detection limit of 0.81 mg/l SO₄^2- respectively together with the RSD of 2.09 % for 10 mg/l SO₄^2- (N=10) were obtained. The proposed method has been applied satisfactorily to the determination of SO₄^2- in commercial beverages. Results obtained by the recommended method were in excellent agreement with those obtained by the reference method verified by using student t-test.

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In this article a mixer with magnetic stirring for flow injection systems, constructed in polyacrylate and PTFE is described. The device was compared with a common T shape mixer. An increase of about 11.7 % on the signal was observed. However the main result is the increase of the precision of spectrophotometric measurements from 5.5 % (RSD) to 2.3 % (RSD).

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A flow immunoassay based on a combined technique of the sequential injection with the beads injection using magnetic microbeads immobilized with antigen or antibody is described. A methodology of the present immunoassay based on chemiluminescence and electrochemical detection and its application to the determination of vitelloginin (Vg) and anionic surfactant, linear alkylbenzene sulfonate (LAS) are described. Magnetic microbeads coated with agarose gel and polylactic acid were used for immobilization of an anti-Vg antibody and an anti-LAS antibody or Vg by a conventional amino coupling method. The introduction, trapping and flushing out of the magnetic microbeads in the immunoreaction cell were controlled by the magnet and the flow of the carrier solution. The protocol of the immunoassay in the immunoreaction cell, introduction of an analyte sample, the enzyme-labeled secondary antibody or antigen and a substrate solution for chemiluminescence or electrochemical detection were sequentially carried out by the sequential injection technique. A lower detection limit around ppb level was achieved for immunoassay for Vg and LAS. The time required for an analysis was ca 15 min/sample including incubation time for immunoreaction.

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