Sorption elution

Moreover, the performance of the sorbent must be suitable for bringing it into contact with the vast volumes of sea water. Most imperative requirements pertain to the uranium uptake kinetics the sorbent should be qualified for a rapid rate of loading in order to minimize the sorbent inventory. The quantity of required sorbent material ms (tons of dry sorbent) is determined by the production rate P (tons of uranium per day) of a projected recovery plant, by the uranium loading b of the sorbent (ppm uranium per cycle based upon dry weight) and by the duration t (days per cycle) of a complete sorption-elution cycle ... 

Implementing SPE in flow analysis without mini-columns is also feasible. To this end, other materials, e.g., commercially available ion-exchange or chelating extraction disks [231], disposable extracting cartridges [232], polymer-composite membranes [233] and monolithic columns [212], have been used. Analytical procedures exploiting addition, transport and disposal of the solid particles, analyte sorption/ elution in flow reversal, and the use of fluidised beads have also been proposed, as highlighted at the end of this section. 

The determination of traces of phenolic species has been successfully accomplished by adaptation of batch standard methods based on the oxidative coupling of the analytes with 4-aminoantipyrine. The online preconcentration of the reaction products using solvent extraction, sorption/elution, or sorbent extraction-based optosensing techniques rendered detection limits below the maximum level recommended by EPA Directives. Interferences caused by colored aromatic amines can be successfully circumvented by analyte enrichment on reversed-phase materials prior to their oxidative coupling. 

So far as ion exchange materials are eontinuously used in the sorption/elution cycles, deterioration of these materials is of primary coneem. Such deterioration can reduce efficiency of the process and contaminate the final produet with outeomes of the polymer decomposition. 

The behavior predicted by this equation is illustrated in Fig. 16-33 with N = 80. Xp = (Evtp/L)/[il — )(p K -i- )] is the dimensionless duration of the feed step and is equal to the amount of solute fed to the column divided by tne sorption capacity. Thus, at Xp = 1, the column has been supplied with an amount of solute equal to the station-aiy phase capacity. The graph shows the transition from a case where complete saturation of the bed occurs before elution Xp= 1) to incomplete saturation as Xp is progressively reduced. The lower cui ves with Xp < 0.4 are seen to be neany Gaussian and centered at a dimensionless time - (1 — Xp/2). Thus, as Xp 0, the response cui ve approaches a Gaussian centered at Ti = 1. 

The results of sorptional properties investigation have shown the possibility of SN-SiO, application for Pb +, ClC+, Zn +, Cd + selective preconcentration. The preconcentrated Cu, Pb, Cd, Zn ions at pH 6-7 were eluted by acid and determined by atomic-absoi ption method. 

Adsorption of lA of POMs with CV and Malachite Green (MG) on the polyurethane foams (PF) and some other adsorbents is investigated. While lA is fully adsorbed on the PF in wide pH range (0,4 M H SO - pH 4) extent of dye adsoi ption does not exceed 0,4%. lA are adsorbed faster then POMs. Extent of sorption of lA is 60-70% at 5 minutes and is complete after 15 minutes. lA can be eluted from PF most effectively by methylbutylketone, acetone or alcohols can be used too. 

The authors repeated the experiment with two, more strongly retained, solutes m-dimethoxy benzene and benzyl acetate. These solutes were found to elute at (k ) values of 10.5 and 27.0 respectively on a silica column operated with the same mobile phase. The results obtained are shown as similar curves in Figure 13. The m dimethoxy benzene, which eluted at a (k ) of 10.5, also failed to displace any ethyl acetate from the silica gel even when more than 0.5 g of solute resided on the silica surface. Consequently, the m-dimethoxy benzene must have also interacted with the surface by a sorption process. 

Enzymic methods are usually very specific and sensitive. Unfortunately the only methods in the literature for carbohydrates are all for glucose. Hicks and Carey [163] reported such a method, with a fluorometric final measurement, which was down to 3 x 10 8 M. Andrews and Williams [ 164] used a preconcentration step, sorption onto charcoal, elution, and a final determination with glucose oxidase. 

The difference between this technique and GC or HPLC is that the separation process occurs on a flat essentially two-dimensional surface. The separated components are not usually eluted from the surface but are examined in situ. Alternatively, they can be removed mechanically for further analysis. In thin-layer chromatography (TLC), the stationary phase is usually a polar solid such as silica gel or alumina which is coated onto a sheet of glass, plastic, or aluminium. Although some moisture is retained by the stationary phase, the separation process is predominantly one of surface adsorption. Thin layers are sometimes made from ion-exchange or gelpermeation materials. In these cases the sorption process would be ion-exchange or exclusion. 

Fissure Elution Experiments. The migration characteristics of americium by water transport in fissures fabricated from gray hornblende schist were determined. Fissures not used in the previous sorption experiments were used for these elution experiments. A diagram of the experimental apparatus is shown in Figure 4. Solution reservoirs were attached above the fissures and the small bore tubes affixed to the bottom of the fissures were connected to solution metering pumps. 

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