Continuous Filters - Separation Columns

A chromatographic column is somehow similar to a filter cascade. However, in the case of a chromatographic column a substance does not stop with the motion in a certain part of the column, as it occurs in a classical filter. Through the column a 

Without going into details, it is sufficient to emphasize that for small times the function approaches the Dirac delta function. This conforms to the usual conditions under those a separation column is operated in practice. 

---

A separation unit Devices that permit continuous separation techniques, for example, dialyzers, filters, adsorbent columns, and exchange resins. 

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

The space between inner and outer cylinders forms the annulus. The column bottom plate is made of stainless steel and typically contains 90 exit holes below the annulus. The holes are covered by a filter plate to keep the stationary phase in place. Three different column sizes are available for the laboratory P-CAC unit the physical characteristics of the different annular columns are summarized in Table 1. The collection of the different fractions at the lower end of the annular column is regulated by a fixed glide ring system. Each chamber in the fixed glidering corresponds to an exit holes in the bottom plate of the column. The number of exit holes equals the number of chambers. The fixed glide ring system allows the continuous and controlled recovery of the separated fractions at the end of the column. Thus cross contamination is avoided and precise fraction collection is ensured. The whole process of collecting the fractions is conducted in a closed system. Unused eluent can be easily recycled. 

Continuous separation systems, optional elements such as dialysers, hquid-hquid extractors, sorption or ion-exchange columns and filters, that can be placed before the reaction coils to remove potentially interfering species. 

Two grams of sodium were dissolved in absolute alcohol, freshly distilled over quicklime, in a flask fitted with a reflux condenser. As sodium ethoxide began to separate out, more alcohol was added until just sufficient was present to retain the product in soln. at the room temp.—40 c.o. were needed. The flask was fitted with a 2-hole stopper fitted with delivery and egress tube to which calcium chloride tubes were attached. Hydrogen sulphide washed in water, and dried by a long column of calcium chloride was passed rapidly into the soln. A fine crystalline precipitate formed in the soln., and increased in amount with the continued passage of the gas. When the soln. was sat. with gas, the precipitate was collected, rapidly filtered, washed with absolute alcohol, and dried in vacuo over calcium chloride. The precipitate weighed 0 25 grm. When benzene or ether is added to the soln., a precipitate of pure anhydrous sodium hydrosulphide is obtained. This is washed and dried as before. 

---