Columns bridged packing

Procedure (See Chromatography, Appendix IIA.) Use a suitable gas chromatograph equipped with a thermal conductivity detector (F and M Model 810, or equivalent), containing a 0.61-m x 6.35-mm (od) stainless steel column (Perkin Elmer Instruments, or equivalent) packed with 20% Silicone SE-30, by weight, and 80% Diatoport S (60- to 80-mesh), or equivalent materials. Program the column temperature from 100° to 270°, heated at a rate of 15°/min. Set the injection port temperature to 300° the bridge current at 140 mA and the sensitivity, lx for the integrator (Infotronics CRS-100, or equivalent) and 2x for the recorder. Use helium as the carrier gas, with a flow rate of 100 mL/min. 

Figure 17-2. Performance of 2.1- x 100-mm columns packed with 1.7-, 3.5-, and 5- xm particles. Stationary phase was bridged-ethyl hybrid CIS prototype material in each case.

Monolithic columns do have disadvantages. Although very high flow rates are used to speed up separations, this generates a considerable amount of solvent waste for >4.6-mm-bore columns. The number of phases and column sizes is very limited at present, as is the number of commercial manufacturers. Also, the technology of particle-packed columns is not static, but continues to improve as well. Monolithic columns have not yet demonstrated the performance capabilities exhibited by sub-2-pm particles and UHPLC. However, advances in monolithic column technology in the years to come promise to bridge that gap. 

A few applications have employed conventional packed columns, although recent developments in new thermally stable stationary-phase materials have generated a renewed interest and the temperature stability of the different stationary-phase materials has been reviewed by Claessens and van Straten [43]. The new materials have included stable metal oxide materials, based on zirconia (Figures 18-4 and 18-5) and titania [44, 45] and hybrid phases combining silica and methylene or ethyl bridges [46]. These have been applied in a number of applications to pharmaceutical compounds (Table 18-1). 

Kuhn, with his column, reached a concentration of 6 at. % of 0. Dostrovsky and his collaborators at the Weiszmann Institute in Israel [53], prepared of about 95% purity and of about 2%. The preliminary concentration from 0.2 to 1.6% of 0 was carried out in 10 columns connected in parallel (diam. 100 mm). The multistage cascade (diam. 80—100 mm) was fed at 800 ml/h and was operated with a takeoff ratio of 1.37 X10. The procedure is to be improved so as to produce a concentration of 99.8%. The highest concentration of is present at the centre of the cascade (<%i 10%). In these separations the Dixon packing, made of 100 mesh phosphor bronze wire gauze in the shape of a Raschig ring with an S-shaped bridge, proved its value... 

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