Column separation and preconcentration systems

Schuster M and Schwarzer M (1998) A new online column separation and preconcentration system... 

FI manifolds for column separation and preconcentration in spectrophotometry are diverse, and there is hardly one which may be considered typical. However, the reader may refer to the manifold used in the determination of boron just mentioned (63]. Another interesting contribution by Novikov et al.[ll] combined ion-exchange column preconcentration with on-line solvent extraction followed by spectrophotometric detection. The eluate from the column preconcentration was released into an on-line liquid-liquid extraction system. An advantage of this approach is that interferences from Schlieren effects are avoided, since the eluate does not flow directly to the detector. Selectivity and sensitivity are also enhanced due to the combination of two separation procedures. The system has been used successfully for the determination of lead in alloys, soil leachates and sea water. 

Although applications for column separation or preconcentration systems coupled to chemiluminescence determinations are few, published reports show no particular difficulties in such applications, except for the requirement of an adjustment of the chemical conditions of the eluate to suit the chemiluminescence reaction. Interferences due to refractive index effects are not likely to occur, owing to the often used spiral shape of the chemiluminescence flow-cell and to the fact that light emission is measured perpendicular to the direction of the flow. Therefore, column washing is usually not as important as for spectrophotometric applications, so that time-based sample loading manifolds such as those used for flame AAS may be used to advantage for improving the concentration, efficiencies. 

The use of LOV allows the bead injection process, so that the replacement of the resin packing was performed automatically. Contrary to the longer manual protocol to isolate Sr which lasts days, the automatic separation and preconcentration system allowed analyzing up to five samples per hour depending on the preconcentrated volume. The analytical protocol started with the automatic filling of the microcolumn with Sr-resin. Then it was conditioned with 2 ml of 8 mol/1 nitric acid. Once the column was ready, a variable volume of sample was dispensed toward the column. An additional volume of 0.5 ml of conditioning solution was propelled in order to eliminate interferences. After that, the elution of Sr was carried out dispensing 5.1 ml of 0.01 mol/1 nitric acid. For the radiostrontium quantification, the eluate was dried and measured in a LBPC. 

In 1994, Dadfarnia and McLeod described the analysis of uranium in surface waters and sea water using a simple FI system with an alumina column for preconcentration.77 Species eluted from this column were delivered to an ICP-MS as the detector. Also in 1994, Hollenbach et al. described the automation of extraction chromatographic methods based on TRU-Resin and TEVA-Resin to separate and preconcentrate U, Th, and Tc from soil samples, using ICP-MS for detection.49125 In 1996, Aldstadt et al. described the use of FI and extraction chromatography using TRU-Resin to determine U in environmental samples by ICP-MS.78... 

The general merits of FI separation and preconcentration summarized in Chapter 1 are all well demonstrated by FI sorption column techniques. The technique is inherently easier to operate than other separation methods, and the equipment generally more robust. An additional benefit over other separation techniques is its extremely high versatility, owing to the availability of a broad range of choice for different sorbents, complexing systems, and eluents. However, there are some restrictive features which are characteristic... 

FI on-line column separation and/or preconcentration have been applied to various detection systems, including atomic absorption and ICP spectrometers, spectrophotometers and electrochemical detectors. The basic components of the manifolds for different detection systems are quite similar, usually consisting of the following parts ... 

Online separation and preconcentration of thorium and uranium was carried out by means of UTEVA resin. LOV made possible the full automation of the system by the online regeneration of the column. Figure 8.10 shows a scheme of the flow system configuration. 

U and 232Th determination in biological materials using FI system with column separation for matrix removal and preconcentration ICP-MS 131... 

Hollenbach et al. captured "Tc from standards or soil sample digestates on a TEVA-Resin column for on-line purification and preconcentration prior to ICP-MS determination.49 A wash solution of 0.5 M HN03 was used to remove interferences prior to elution with 8 M HN03 solution. A Re isotope, which behaves similarly to pertechnetate on TEVA-Resin, was used as an internal standard. Recoveries from the column varied from 97 to 99.5%, and columns could be reused over a hundred times. The use of the on-line column separation reduced detection limits by 10-fold and alleviated matrix and isobaric interferences compared to direct sample injection. This pioneering study adapted FIAS-200 and FIAS-400 FI systems to perform sample injection and extraction-chromatographic separations upstream from the ICP-MS. 

The development of solvent-impregnated resins and extraction-chromatographic procedures has enabled the automation of radiochemical separations for analytical radionuclide determinations. These separations provide preconcentration from simple matrices like groundwater and separation from complex matrixes such as dissolved sediments, dissolved spent fuel, or nuclear-waste materials. Most of the published work has been carried out using fluidic systems to couple column-based separations to on-line detection, but robotic methods also appear to be very promising. Many approaches to fluidic automation have been used, from individual FI and SI systems to commercial FI sample-introduction systems for atomic spectroscopies. 

The separation performance and sensitivity of a capillary electrophoresis system coupled to a phosphorous-specific flame photometric detector (FPD) has been reported for the detection of alkylphosphonic acids l20 221. The liquid junction used to decouple the electric field from the FPD showed a negligible influence on the performance of the system as compared with online UV detection. The use of an on-column sample stacking preconcentration technique allowed for injection of 900 nL. With the large injection, the detection limits for the alkylphosphonic acids in water were 0.1-0.5 xgmL 1. 

A U-tube filled with a GC sorbent (e.g. polymethoxysilane coated silica beads) and maintained in liquid nitrogen (where hydrides are trapped) allows the product to be concentrated prior to insertion, either into the detector or onto the column. A thermal desorption system is mandatory for proper, fast removal of retained, preconcentrated species. A water trap (another U-tube maintained at — 15°C or filled with anhydrous CaCl,), a Nafion tube and various other devices are often placed in between the separator and detector. 

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