Automation approaches flow injection analysis

The 1950s saw the introduction of a completely new approach to automation, in the form of continuous flow analysis. This made a significant contribution to the advance of automated analysis and subsequent development has been in the form of flow injection analysis. The original instruments were single channel and capable of measuring only one constituent in each sample. Multichannel instruments were then developed which could simultaneously carry out several different measurements on each sample. These were useful in laboratories where many samples required the same range of tests. 

Routine analyses of large numbers of similar samples can readily be automated and the sample throughput considerably increased (sometimes up to about 200 samples per hour) by carrying out the analyses in a continuously flowing medium. At present there are two basic approaches to the problem, the older technique of continuous-flow analysis (CFA) introduced more than 25 years ago [145] and widely developed by the Technicon Company (Auto-Analyzer), and more recent flow-injection analysis (FIA for a recent literature review see [123]). For a brief comparative survey of the two methods see [148]. 

G.D. Clark, J. Ruzicka, G.D. Christian, Split zone flow injection analysis an approach to automated dilutions, Anal. Chem. 61 (1989) 1773. 

M. A. Koupparis, P. Anagnostopoulou, and H. V. Malmstadt, Automated Flow-Injection Pseudotitration of Strong and Weak Acids, Ascorbic Acid and Calcium, and Catalytic Psudotitrations of Aminopolycarboxylic Acids bu Use of a Microcomputer-Controlled Analyser. Talanta, 32 (1985) 411. A. Rios, M. D. Luque de Castro, and M. Valc rcel, Flow Injection Analysis A New Approach to Pharmaceutical Determinations. J. Pharm. Biomed. Anal., 3 (1985) 105. 

Another area in which PIMs show considerable promise is chemical analysis. The use of PIMs in the construction of ISEs and optodes is well established, but their potential use in analytical separation is only starting to be explored. PIMs are particularly useful in solid-phase extraction (SPE) for preconcentration of analytes [17,18]. Also, Eonths et al. have used a PIM containing Aliquat 336 as the carrier for the preconcentration of Cr(VI) prior to its determination in the membrane by energy-dispersive X-ray fluorescence spectrometry [47]. Flat-sheet PIMs can also be conveniently incorporated into separation modules for use in online analytical techniques such as flow injection analysis. For example, a D2EHPA-based PIM has been used in a separation module incorporated into a flow injection analysis system for the determination of Zn(II) [35]. This new approach has interesting implications for use in automated analysis, particularly in held instruments for the continuous monitoring of pollutants. 

Coulometry may be employed for detection in flow-injection analysis (FIA), an approach to automation of sample handling and processing, or in separation methods such as HPLC. Note that these methods are closely related to amperometric detection. The distinction is in the degree at which the analyte is converted. A high Faradaic efficiency is desirable in any case and 100% efficiency might actually be... 

It is difficult to be automated in its classical form (using a separation funnel or similar apparatus), although a number of flow-system LLE approaches have been presented, applying the principle of flow injection analysis. 

Flow injection Analysis (FIA) is a popular approach for automation of chemical analysis and the technique has been adapted successfully in various... 

Fig. 3. Plasma sodium analysis results obtained with a PVC membrane electrode based on 1 compared with a SMAC analyser. The electrode was part of an array of ISEs which were carefully calibrated before use. Bias in the results was eliminated through the use of a flow-injection analysis (FIA) approach which enabled the entire sample handling and analysis to be automated. These results demonstrate clearly the successful application of calix[4]arene-based ISEs to this important assay (from reference [15] with permission).

A number of other FIA approaches for anionic determination have been proposed, although it is doubtful that they are much used. For example, determination of high concentrations of LAS can be performed based on the solvatochromism of p-diphenylaminoa-zobenzene sulfonate (80). Another method for automated analysis of anionic surfactants involves flow injection analysis with continuous formation and extraction of the ion pair with copper(II)-l,10-phenanthroline. The extract is introduced into an atomic absorption spectrophotometer for determination of the copper (81). Cationics can be determined similarly, using adduct formation with tetrathiocyanatocobaltate(II) (82). The last system is tolerant of interference by ethoxylated nonionic surfactants, since potassium ion is not added. 

In another approach the electrocatalytic activity of lead oxide was enhanced with fluoride doping. The F-doped lead oxide-modified electrode leads to the fabricatirai of an electrochemical detection system for flow injection analysis to detect the chemical oxygen demand (COD) in water samples. The combination of flow injection analysis with electrochemical detection of COD results in the development of a low-cost, rapid, and easily automated detection system with minimum reagent consumption. The basic principle of the F-doped lead oxide electrode is the generation of hydroxyl radicals which are subsequently utilized for the oxidation of COD pollutants in order to determine the COD value. It is a multistep process at first, hydroxyl radicals will be produced at the surface of the F-PbOa electrode by the anodic discharge of water ... 

Fluidic approaches move samples, reagents, and eluents from place to place entirely through a system of pumps, valves, and tubing. Fluidic methodology from the field of flow injection (FI) analysis has been adapted to the needs of automated radiochemistry. In its original form, FI used a multichannel peristaltic pump and an injection valve in a continuous forward flow paradigm to mix the sample with reagents and... 

Other alternative options for PAHs extraction coupled to flow injection are static, dynamic, and static-dynamic-pressurized liquid extraction. They have been applied to contaminated soils analysis, allowing the partial automation of the proposed approaches. Efficiencies close to 100% have been obtained with the three operational modes. However, the static-dynamic mode has proved as the most suitable alternative providing the shortest extraction time (25 min) versus the static (30 min) and the... 

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