Dialysis, automatic

FIA star 5010 Modular, semi- or fully automatic operation. May be operated with process controller microprocessor. Can be set up in various combinations with 5017 sampler and superflow software which is designed to run on IBM PC/XT computer 60-180 samples h Dialysis for in-line sample preparation and in-line solvent extraction.Thermostat to speed up reactions. Spectrophotometer (400-700nm) or photometer can be connected to any flow through detector, e.g. UV/visible, inductively coupled plasma, atomic absorption spectrometer and ion-selective electrodes... 

Even complex procedures can be automated, such as dialysis to clean up dirty samplers, solvent extraction, automatic distillation and on-hne UV digestion. Unhke the earlier AutoAnalyzer systems which use a purely step-wise autosampler, the TRAACS is fitted with a random-access sampler as standard. 

The second half of the 1990s saw an increase in the use of dialysis (as a liquid-liquid extraction procedure). Its main advantage is the possibility of operating in an automatic mode by coupling a dialysis unit with an automatic injector, as demonstrated not only in HPLC analysis (17) but also in flow-injection determinations of reducing sugars in wines (18) and alcoholic fermentation broths (19). 

It was seen that the two readily diffusible substances, glucose and urea, did not dialyze at equivalent rates and that protein binding of calcium had to be overcome to obtain a dialysis rate proportional to its concentration. The instrument usually provides a dialysis rate (and therefore an amount dialyzed) which is proportional to the concentration of the substance being tested. However, this proportionality would need to be checked for any test adapted to automatic analysis. It was also seen that dialysis was influenced by the presence of protein, salts, membrane charges, etc., in that dialysis rate from standards was not always identical with that from plasma or serum. To date these differences have been corrected for by a constant factor. 

Solid phase extraction systems have been suceessfully automated (for example in the ASPEC system, marketed by Gilson). This allows samples to be applied to the cartridge and is linked on-line to the HPLC. An extension of this is the ASTED which combines dialysis with trace enrichment on a solid phase and is automatically coupled to the HPLC. These... 

Separations by dialysis, by liquid/liquid extraction, and by gaseous diffusion are leadiiy canied out automatically with flow-injection sy.stems. 

Figure 12 shows a possible set-up for hemodialysis monitoring. Patients blood is pumped through a dialysis cell, and low molecular weight substances including urea are removed by a semipermeable membrane (cut off 10 kD) and dialysis buffer. The urea enriched dialysate passes through an injection valve and enters a waste container. Due to switching the valve, a defined sample volume is pumped to the ET. Here, enzymatic conversion takes place via immobilized urease and provides information about the current urea concentration. Thus, the hemodialysis effect is automatically monitored via urea analysis and makes an individual treatment possible. 

The discrete systems of automatic analysis developed so far have not, in general, solved the problem of deproteinization in a way as satisfactory as the dialysis step adopted in the continuous-flow system. An earlier version of the Robot Chemist included a module in which precipitation of proteins followed by filtration was carried out, and the Mecolab system can incorporate a centrifugation step, following which a sample of supernatant can be automatically aspirated, but both these approaches are relatively cumbersome. Consequently attention has been directed to the development of analytical methods for blood serum or plasma that do not involve a deproteinization stage, but although alternative methods not involving the removal of protein may be feasible for many estimations, the responsibility for confirming the validity of such alternative procedures remains with the analyst. 

Fig. 4.18 Automatic enzymatic determination of D-galactose in serum in a continuous FIA system with liquid dialysis for the removal of interfering macromolecules. Reactors Cu2t, Bond-Elut-NHz-Cu Cat, catalase GalOD, galactose oxidase POD, peroxidase. Absorbent arylamino porous glass. (Reproduced from [14] with permission of Elsevier).

In spectrophotometric methods which incorporate an on-line dialysis system, the acceptor streams are almost always connected to the detector after merging with the appropriate reagents. Dialysis is used mostly to remove interferents, such as suspended or colloidal materials, which interfere physically with the photometric detection but the technique is also often used to achieve different degrees of dilutions automatically. As an early example, Basson and van Staden [14] used an on-line dialyzer to achieve deproteination and dilution of serum samples in the determination of calcium by a cresolpthalein complexone FI photometric method. Owing to the dilution effects and the exclusion of potential interferents, interferences from Schlieren effects, such as those encountered in sorption separation systems (cf. Sec. 4.6.6) were not experienced in on-line dialysis spectrophotometric systems. 

Another method, which is routinely used for gradient determinations is flow dialysis [48]. In this method a compartment containing the membrane preparation and the radioactively labeled solute or indicator molecules is separated from a second compartment via a dialysis membrane. The solution in the second compartment is replaced with a constant rate and the radioactivity in the outflowing solution is monitored. The radioactivity monitored reflects the concentration of the radioactive probe in the external medium in the first compartment. Recently, an automatization of this technique has been described which considerably increases the... 

Hyphenation of automatic continuous flow systems (such as SPE, dialysis, gas diffusion, evaporation, direct leaching, etc.) to CE and the coupling of automatic sample preparation devices into commercial CE equipments have been devised as a means to simplification and miniaturization of analytical procedures. An automatic online SPE device for the multiresidue extraction of seven pesticides has been described. Four river samples were spiked with the test mixture at three different levels presenting recoveries Irom 90% to 114%. 

It should be noted, however, that use of plastics or rubbers in various applications where contact with food is involved should not automatically mean that its use will result in adverse health effects. A number of plastics and rubbers are being used in many critical areas already without any problems, such as food packaging materials and in the health sector (i.e., blood bags and dialysis tubing). In fact, in most cases, it is not the plastic or rubber material itself, but certain additives and other foreign chemicals (that are added for different purposes or that are produced in the systems somehow), that can be the source of the problems that can pose health hazards, hence they should be considered carefully. 

Flow techniques are particularly suitable for monitoring environmental parameters in waters. Moreover, flow methods offer unique possibilities for automatic sample pretreatment, involving inline dilution or filtration, adjustment of viscosity, ionic strength, or pH as well as removal of solid and colloidal matrix constituents via in-line dialysis separation techniques. 

Another method is automatic peritoneal dialysis (APD), whereby a machine performs the irrigation during the night. There are advantages and disadvantages to haemodialysis and peritoneal dialysis. 

Table 18.4 Characteristics and figures of merit for automated solid-phase extraction of ribofiavin and determination by HPLC-FL. The procedure proposed by Greenway and Kometa (1994) is based on automatic SPE using a commercial flow-through column with silica Cl8. Samples are first digested by microwave irradiation and small molecules were separated by dialysis prior to SPE. The SPE extract is subsequently analyzed by reversed phase chromatography.

Using an agarose derivative of anti-(pregnancy zone protein) antibody, the use of an automated immunospecific affinity chromatography system for continuous use has been demonstrated for the purification of pregnancy zone protein. The automated system includes time-controlled sample application, washing and elution steps, and automatic dialysis of eluted fractions. 

Self-absorption 0.3 Standard Normal 1 0.3 Automatic in spectrum dialysis... 

The measurement of Na, K, Mg, and Ca by FAES or EAAS techniques usually requires dilution of the water sample, considering that their natural concentrations exceed the linear range of the methods. The use of an FIA system with a dialysis imit for the automatic determination of Ca and Mg by FAAS, and Na and K by flame photometry in wastewater has been reported [121,126,127]. Other researchers [124,128,129] have used... 

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