J. Růžička

Flow injection analysis : Part X. theory, techniques and trends

Abstract The dispersion of sample zones in Flow Injection systems is described by analogy with the mixing of fluids in large-scale chemical reactors. This comparison has resulted in a definition of the sample zone dispersion, its mathematical description, and the identification of the main parameters which can be used to effect the desired degree of mixing. The miniaturized Flow Injection system, designed with the aid of the rules derived on the basis of the theory of dispersion, uses only 5–30 μl of sample solution and gives the analytical readout within 5–30 s after sample injection. The most recent Flow Injection methods, such as pH measurements at limited dispersion, voltammetry (including anodic stripping at trace levels), solvent extraction, and a new approach to enzymatic assays, are briefly reviewed to illustrate the trends towards future developments in continuous analysis in unsegmented streams.

Flow injection analysis. principles, applications and trends

Abstract The basic principles of Flow Injection Analysis are outlined. The parameters governing the dispersion of the injected sample zone in the system are discussed, and it is demonstrated how these parameters can be manipulated in order to suit the requirements of an individual analytical procedure. A number of examples illustrating the practical application of f.i.a. are described, comprising the use of automated, stopped-flow, merging-zones, extraction techniques as well as f.i.a. scanning and methods based on intermittent pumping. Updated lists on f.i.a. procedures published and species that can be determined by f.i.a. are included.

An efficient flow-injection system with on-line ion-exchange preconcentration for the determination of trace amounts of heavy metals by atomic absorption spectrometry

Abstract A flow-injection system with on-line ion-exchange preconcentration on dual columns is described for the determination of trace amounts of heavy metals at μg l−1 and sub-μg l−1 levels by flame atomic absorption spectrometry. The degree of preconcentration ranges from 50- to 105-fold for different elements at a sampling frequency of 60 s h−1. The detection limits for Cu, Zn, Pb and Cd are 0.07, 0.03, 0.5, and 0.05 μg l−1, respectively. Relative standard deviations were 1.2–3.2% at μg l−1 levels. The behaviour of the different chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of sea water.

Combination of flow injection analysis with flame atomic-absorption spectrophotometry: determination of trace amounts of heavy metals in polluted seawater

A simple flow injection system, the FIAstar unit, was used to inject samples of seawater into a flame atomic-absorption instrument allowing the determination of cadmium, lead, copper and zinc at the parts per million level at a rate of 180–250 samples per hour. Further, on-line flow injection analysis pre-concentration methods were developed using a microcolumn of Chelex-100 resin, allowing the determination of lead at concentrations as low as 10 parts per 109(p.p.b.) and 1 p.p.b. for cadmium and zinc. The sampling rate was between 30 and 60 samples per hour and the readout was available within 60–100s after sample injection; the sampling frequency depended on the pre-concentration required.

Selectrode—the universal ion-selective electrode: Part VI. The calcium(II) selectrode employing a new ion exchanger in a nonporous membrane and a solid-state reference system

Abstract The correlation between extraction data and electrode behaviour assisted in explaining the vital properties of organophosphate-based calcium electrodes, and in suggesting a new liquid ion exchanger, di-(n-octylphenyl) phosphoric acid. This compound has been synthesized and used in various electrode constructions including a newly developed membrane selectrode with a solid-state inner reference system. The resulting calcium(II) selectrode, calibrated in a series of calcium buffers, has been subjected to potential-pH measurements, and used in EDTA titrations. The selectivity parameters of this electrode towards Na + , H + and other foreign ions were found to be substantially better than those of any other calcium sensors previously described.

Flow injection analysis : Part IX. A New Approach to Continuous Flow Titrations

Abstract Studies of dispersion patterns in nonsegmented streams, flowing through narrow open tubes, show that it is possible to obtain highly reproducible concentration gradients within a sample zone injected into the moving stream. By varying the geometry of the flow path, low, medium and high dispersion patterns can be achieved; the high dispersion pattern forms the basis for a new approach to continuous flow titrimetry. In this type of titration, discrete samples are passed through a gradient device and are then mixed with a continuously flowing stream of titrant of fixed concentration. The new technique has been tested for potentiometric as well as spectrophotometric end-point indication. A simple one-channel system allows titrations to be performed automatically in less than 1 min.

Selectrode—the universal ion-selective electrode : Part VII. A valinomycin-based potassium electrode with nonporous polymer membrane and solid-state inner reference system

Abstract A potassium electrode utilizing a solution of valinomycin in diphenylether and a porous membrane is compared with selectrodes in which the diphenylether has been replaced by a suitable plasticizer and the porous membrane support by a polymer net-work. The development of the polymer membrane allows the use of simplified selectrode construction with a “solid-state” calomel reference system; Rules for a successful choice of a suitable solvent-polymer combination are suggested and used for development of new Polyvinylchloride- and polyurethane-based membranes.

Flow injection analysis: Part VII. Use of ion-selective electrodes for rapid analysis of soil extracts and blood serum. Determination of potassium, sodium and nitrate

Abstract The flow injection principle is used with novel design of a flow cell, in which the ion-selective and reference electrode are incorporated. The reproducible mixing of the sample with the carrier stream of electrolyte and the precise timing of potentiometric measurements in the continuously moving stream are the most important parameters influencing the quality of direct potentiometric measurements. Methods for the determination of nitrate and potassium in soil extracts, and sodium and potassium in blood sera are described. At sampling rates of 125 determinations per hour, a standard deviation of only 0.8 % is typical. Simultaneous measurements of two ions on one stream are described; advantages and drawbacks of the use of ion-selective electrodes in continuous flow measurements are discussed; and the new possibilities which the flow injection method offers are contemplated.

Stopped flow and merging zones — a new approach to enzymatic assay by flow injection analysis

Abstract Four alternative flow injection methods based on the concept of merging zones have been developed for the assay of glucose in serum with glucose dehydrogenase. Special attention has been paid to the dispersion and synchronization of the merging zones and to methods of measuring the blank value of serum. The optimal procedure, based on rate measurements, allows the assay of glucose to be done at a rate of 100 determinations per hour, with the analytical readout available 30 s after sample injection. The assay requires less than one unit of enzyme per sample.

Flow injection analysis. Part VI. The determination of phosphate and chloride in blood serum by dialysis and sample dilution.

Abstract The rapid determination of chloride and inorganic phosphate in blood serum based on continuous flow spectrophotometry was adapted to Flow Injection Analysis by applying dialysis as well as differential dilution of the injected samples. In addition to the manual injection procedure, an automated microsampling unit was developed and used. By continuous dialysis, chloride could be determined reproducibly at a sampling rate of 125 samples per hour at sample volumes of 60 μl or less. A similar sampling rate and high precision were obtained for the determination of inorganic phosphate by using differential dilution.