Ion-exchange Disks

How long does an IC column need to be for an effective separation. Separation of anions on monoliths 5-10 mm in length was described in Section 3.3.1. In some cases an anion-exchange disk can function as an effective column even though the diameter of the disk is much greater than that of the mobile phase path through the disk. The growing use of short monolithic beds in the form of one or more disks placed in a tube has been reviewed [52]. 

Cellulose membranes similar to filter paper can be used to concentrate ions from aqueous samples without retaining most neutral solutes. The -CH2OH groups of the cellulose are functionalized to introduce either diethylaminoethyl groups (to prepare an anion exchanger), or sulfopropyl groups to prepare a cation exchanger. 

The 3M Co. produces membrane disks containing embedded ion-exchange particles. Each disk is 1 mm in thickness and a small disk of any convenient diameter can be cut from a larger sheet with a cork borer. The practical use of the small disks is illustrated by a 15-s separation of chromium(III), which is a 3-i- cation, and anionic chromium(Vl), which exists primarily as HCr04 [53], 

Two small extraction disks are placed one on top of the other in a plastic holder. Then a syringe containing the aqueous sample is attached to the holder and the sample is pushed through the disk at a rate of about 4—5 mb min . AU of the chromium(VI) is retained on the top anion-exchange disk and the chromium(III) is extracted by the second cation-exchange disk. The concentrations on each disk are several hundredfold higher than they were in the original sample. The amounts of chromium(IIl) and (VI) extracted were measured directly on the surface of the respective disks by diffuse reflectance spectroscopy (DRS). 

1121 I S. Fritz, Factors affecting selectivity in ion chromatography,/. Chromatogr. A, 1085, 8, 2005. 

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Recombinant human Tumor Necrosis Factor Purification, comparison with conventional columns Ion Exchange disks, Hydro-phobic Interaction disks [72]... 

The ion-exchange disks are available from a number of manufacturers (Table 6.1 and Appendix Product Guide). The disks typically have from 0.2 to 0.4 meq/disk (47 mm) exchange capacity. The disks manufactured by 3 M (Empore disks) are made from a styrene-divinylbenzene copolymer therefore, they do not have the problem of the silica-based disks with limited pH range. The Empore disks also come in a chelation disk for the removal of trace metals from solution, as well as in strong anion-exchange form (Fig. 6.1). 

Recently, isolation and derivatization have been combined using both silica sorbents modified with specific derivatization agents, derivatization on ion-exchange disks, and semipermeable membrane devices. 

Ash 10-g sample with sulfur. Dissolve residue and absorb metals on ion exchange disk. 

Table 8.4 shows the results that were obtained by analyzing trace metals on ion exchange disks. Since these disks were prepared by treatment with solutions of metal salts of known concentration, the precision data give an estimate of the error associated entirely with the ion exchange and measurement steps of the method. 

Recovery of Metals on Ion Exchange Disk Using Internal Standard... 

XRF Analysis of a Synthetic Unknown Using an Ion Exchange Disk with an Internal Standard... 

An Empore ion-exchange disk inserted into a tube is ideal for this use. 

Supercritical fluid extraction (SFE) has been used mostly in environmental analysis [129,205] for the extraction of nonpolar organic pollutants from solid samples, for example, sediments. The technique has abo been used together with SPE dbks (silica Cis, polymeric, and ion exchanger disks) for the extraction of phenols from water samples followed by GC-MS [206]. After adsorbing the phenols onto the SPE disk, they are eluted with a supercritical fluid (carbon dioxide). 

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