Automated flow system, with

An automated flow system has also been used by Foresti et al. to form CdS layers, with up to 150 cycles, using pH 9.2 solutions for both elements on Ag(lll) electrodes [116], In their case, the deposits appeared stoichiometric, without the excess S previously observed by this group [111]. Their cycle produced relatively thin deposits, similar to this author s, or about 1/3 ML/cycle. 

Hua et al. [595] have described an automated flow system for the constant-current reduction of uranium (VI) onto a mercury film-coated fibre electrode. Interference from iron (III) was eliminated by addition of sulfite. The results obtained for uranium (VI) in two reference seawater samples, NASS-1 and CASS-1, were 2.90 and 2.68 g/1, with standard deviations of 0.57 and 0.75 g/1, respectively. 

Immunosensors have been developed commercially mostly for medical purposes but would appear to have considerable potential for food analysis. The Pharmacia company has developed an optical biosensor, which is a fully automated continuous-flow system which exploits the phenomenon of surface plasmon resonance (SPR) to detect and measure biomolecular interactions. The technique has been validated for determination of folic acid and biotin in fortified foods (Indyk, 2000 Bostrom and Lindeberg, 2000), and more recently for vitamin Bi2. This type of technique has great potential for application to a wide range of food additives but its advance will be linked to the availability of specific antibodies or other receptors for the various additives. It should be possible to analyse a whole range of additives by multi-channel continuous flow systems with further miniaturisation. 

Immunometric Assays Using an Automated Flow System Equipped WITH A FIapten-Immobilizing Affinity Column... 

In 1970, Eckman et al. devised the automation of a quantitative immunochemical analysis of transferrin (El). In this automated flow system, diluted samples were allowed to react with antitransferrin antiserum serially and the degree of light scattering of the resulting turbidity was measured in the fluorometer, used as a nephelometer. The optimal conditions for nephelometry were extensively studied. Subsequently, Buffone reported... 

Finally, the possibilities of automation of amperometric and voltammetric electroanalysis should be stressed, as well as the use of solvents other than water43. Pulse techniques are semi-automated by nature the responses can be transmitted directly to a microcomputer for immediate analysis. Fast on-line analysis in flow systems with automated calibration is one of the great advantages, which will be much exploited in the future. 

Figure 12.2. Microcolumn flow-through manifolds for fractionation analysis in environmental solids (ti) continuous-flow system with either fraction collection or online detection (Jj) flow-injection setup with discrete injection of extractant (c) sequential injection system as assembled for fully automated sequential or single extractions. MC microcolumn, C coil, SP syringe pump, PP peristaltic pump, R reagent, D detector, W waste, SV selection valve, IV injection valve. (Adapted from Mir6 et al., 2005a.)...

Figure 1. Advantages and trade-offs of new analytical techniques for stable isotope analysis (see Table 1). At present, the best accuracy and precision is achieved for 5 0 by IR-laser fluorination of chips or powdered samples the fastest and least expensive analyses are made by automated pyrolysis systems with continuous flow mass-spectrometers (CFMS) and the smallest samples and best in situ spatial resolution is attained by ion microprobe. The capabilities of in situ UV-laser fluorination are intermediate.

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

Viscosimetric measurements of surface-active samples in capillary viscosimeters are often hindered by vesication. In addition to a variation of the running times by bubbles of air in the reservoir and the no longer existing laminar flow profile in the capillary, an exact determination of the running times is not possible, because the foam formation on the fluid meniscus interface is particularly strong. Especially fully automated viscosimeter systems with light barriers at the marks Mi and M2 provide no exact data in this case. 

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 ... 

However, increasing environmental concerns have fostered the development of automated analytical systems for environmental monitoring with added features for in situ, real time and remote operation. The use of electrochemical sensors as detectors integrated in automated flow systems has proved to achieve simple, robust, and automatic analyzers for enviromnental monitoring. 

Figure 2.16 Clirotnatograms of a pentane extract of a water sample containing 200 ppb of a naphtha fraction (a) sample extracted by using a continuous flow system, where a pressurized bottle was employed as the sample-delivery system (b) batch-extracted sample. Reprinted from Journal of Chromatography, A 330, J. Roeraade, Automated monitoring of organic Race components in water. I. Continuous flow exti action together with on-line capillary gas cliro-matography , pp. 263 - 274, copyrigth 1985, with permission from Elsevier Science.

In 1990, Bushey and Jorgenson developed the first automated system that eoupled HPLC with CZE (19). This orthogonal separation teehnique used differenees in hydrophobieity in the first dimension and moleeular eharge in the seeond dimension for the analysis of peptide mixtures. The LC separation employed a gradient at 20 p.L/min volumetrie flow rate, with a eolumn of 1.0 mm ID. The effluent from the ehromatographie eolumn filled a 10 p.L loop on a eomputer-eontrolled, six-port miero valve. At fixed intervals, the loop material was flushed over the anode end of the CZE eapillary, allowing eleetrokinetie injeetions to be made into the seeond dimension from the first. 

A complicated analyser system such as that described above can only be maintained if all of the valve-switching events are scheduled in the correct positions in the chromatogram. Mismatch of one of the events will cause (parts of) components to be directed to the wrong columns and thus possible misidentifications. Therefore, accurate determination and maintenance of the cutting windows are essential. This can only be accomplished in a fully automated system with accurate flow and temperature controls. Once these prerequisites are fulfilled, the system will operate unattended and produce results of high quality. The repeatabilities generally achieved are of the order of 1 % rel. 

An area worthy of study is the development of systems of increasing sample throughput beyond the single column operation. Scott has introduced a prototype multicolumn system based on the centrifugal analyzer principle (53). In this set-up a series of LC colimns is rotated on a disc, with sample delivery at the center of the disc and elution and spectrophotometric analysis on the outside. He has suggested using affinity columns for rapid serum protein analysis by this approach. Of course, other principles, such as segmented flow, could be envisioned in an automated LC system as well. Undoubtedly, we can expect to see the availability of such systems in the next few years. 

In a similar way, electrochemistry may provide an atomic level control over the deposit, using electric potential (rather than temperature) to restrict deposition of elements. A surface electrochemical reaction limited in this manner is merely underpotential deposition (UPD see Sect. 4.3 for a detailed discussion). In ECALE, thin films of chemical compounds are formed, an atomic layer at a time, by using UPD, in a cycle thus, the formation of a binary compound involves the oxidative UPD of one element and the reductive UPD of another. The potential for the former should be negative of that used for the latter in order for the deposit to remain stable while the other component elements are being deposited. Practically, this sequential deposition is implemented by using a dual bath system or a flow cell, so as to alternately expose an electrode surface to different electrolytes. When conditions are well defined, the electrolytic layers are prone to grow two dimensionally rather than three dimensionally. ECALE requires the definition of precise experimental conditions, such as potentials, reactants, concentration, pH, charge-time, which are strictly dependent on the particular compound one wants to form, and the substrate as well. The problems with this technique are that the electrode is required to be rinsed after each UPD deposition, which may result in loss of potential control, deposit reproducibility problems, and waste of time and solution. Automated deposition systems have been developed as an attempt to overcome these problems. 

From the time when it was shovm that micro flow reactors can provide valuable contributions to organic chemistry, it was obvious to develop them further and their workflow towards modern screening techniques [20]. It was especially the finding of high reaction rates, the capability to transport and transform minute sample volumes and the first integration of analytics that paved the way to a parallelization of micro flow processing. These benefits were combined with the ease of automation of a micro flow system. By this means, the potential of on-line analysis of the reactions can be fully exploited. 

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