Columns preparative

S-Acetylthiocholine chloride [6050-81-3] M 197,7, m 172-173° The chloride can be purified in the same way as the bromide, and it can be prepared from the iodide. A few milligrams dissolved in H2O can be purified by applying onto a Dowex-1 CL resin column (prepared by washing with N HCl followed by COf— free H2O until the pH is 5.8). After equilibration for lOmin elution is started with CO3—free distilled H2O and... 

Table 6.7 shows the available preparative columns and corresponding analytical columns. Preparative columns are also available in larger diameters of up to 50 mm. 

Ion exchange column. Prepare the Chelex-100 resin (100- 500 mesh) by digesting it with excess (about 2-3 bed-volumes) of 2M nitric acid at room temperature. Repeat this process twice and then transfer sufficient resin to fill a 1.0 cm diameter column to a depth of 8 cm. Wash the resin column with several bed-volumes of de-ionised water. 

Columns prepared with from 5-7.5% loadings of OV-101 performed equally well. At a concentration of 10% OV-101 a small increase in sultone response is observed but the efficiency of the columns declines. Below 5% OV-101 concentrations the separation of the sultone components decreases significantly. 

In its turn, PLC can be used as a pilot technique for column preparative chromatography with the same system of mobile and stationary phases. 

Glass chromatography column 400 x 15-mm i.d. with a stopcock Column preparation A silica gel column is prepared by packing a slurry of silica gel (10 g) in n-hexane-acetone (9 1, v/v) into a glass chromatography column. About a 1-cm layer of anhydrous sodium sulfate is placed above and below the... 

Transfer the residue with 2 x 1 mL of DMSO into a 10-mL centrifuge vial. Add 20 iL of methyl iodide and 200 pL of 1M sodium hydroxide solution, mix and plug the vial with a stopper. Derivatization is done at 70 °C for 1 h. After addition of 45 mL of aqueous 10% sodium chloride, extract the reaction mixture with 10 or 2 x 10 mL of n-hexane. Transfer the n-hexane phase on to the chromatographic column prepared as described below. 

Continuous Improvements in column technology have made many of the early studies on column preparation obsolete. We will present only a brief account of these older methods in the following sections. For a more extensive view of the evolution of column technology standard texts [136-142] and review articles [35,143-146] should be consulted. 

Thixotropic suspensions are generally required for static coating due to the long column preparation time. 

Before discussing column preparation procedures a few comments on nomenclature are in order. Open tubular columns are also widely known as capillary columns. The characteristic feature of these columns is their openness, which provides an unrestricted gas path through the column. Thus open tubular colximn rather than capillary column is a more apt description. However, both descriptions appear frequently in the literature and can be emsidered interchangeable. The type of columns discussed so far are also known as wall-coated open tubular columns (WCOT). Here the liquid phase is deposited directly onto the column wall without the inclusion of any additive that might be considered as... 

Solutions to the above problea are required if efficient open tubular colunns are to be prepared. The energy of the saooth glass surface can Sse Increased by roughening or chemical Modification, or the surface tension of the stationary phase can be lowered by the addition of a surfactant. Roughening and/or cheMical modification etre the most widely used techniques for column preparation the addition of a surfactant, although effective, modifies the separation properties of the stationary phase and may also limit the thermal sted>ility of columns prepared with high temperature stable phases. 

Figura 2.9 Dse of th Grob test Mixture to compare tbe activity of various glass surfaces coated with ov-ioi. Surface types A > Untreated pyrex glass, B pyrex glass deactivated by thermal degradation of Ceurbowax 20M, C < SCOT column, prepared with Silanox 101, D pyrex glass column coated with a layer of barium carbonate and deactivated as in (B), and E - untreated fused silica. Components are identified in Table 2.7 with ac - 2-ethylhexanoic acid. (Reproduced with permission from ref. 152. Copyright Elsevier Scientific Publishing Co.)...

There are surprisingly few studies of the retention mechanism for open tubular columns but the theory presented for packed columns should be equally applicable. For normal film thicknesses open tubular columns have a large surface area/volume ratio and the contribution of interfacial adsorption to retention should be significant for those solutes that exhibit adsorption tendencies. Interfacial adsorption has been shown to affect the reproducibility of retention for columns prepared with nonpolar phases of different film thicknesses [322-324]. The poor reproducibility of retention index values for columns prepared from polar phases was demonstrated to be c(ue to interfacial... 

---