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Column packing viscous

Alternatively we may want to keep the inlet pressure of the column low (19). This approach is interesting in terms of safety and equipment lifetime. Furthermore the use of columns packed with fine pardcles is most promising at relatively low inlet pressures so that the pressure does not exceed the practical limit of the instrument when moderatelj viscous solvents are used. Finally, pumps capable of working at moderate pressures up to 70 atm are less expensive than those currently used in HPLC. It should be noted, however, that a separation is accomplished at the lowest inlet pressure when the column is packed with the largest particles available. In this case very long columns and extremely long analysis times are required. [Pg.183]

In a 50-ml three-necked flask are placed the carboxylic acid (0.01 mol), ethyl polyphosphate (6g, PPE) and purified chloroform (5 ml). The mixture is cooled in an ice bath and the flask is connected to a balloon containing ammonia gas ( 3 litres). Air in the flask is replaced with ammonia and the mixture is mechanically stirred at 0-5 °C for 30 minutes and then at room temperature for one and a half hours whereupon the mixture turns very viscous (1). The balloon is removed and PPE (10 g) is added. The stirring is continued at 80 °C until the reaction is complete (usually within several hours) the dehydration is monitored by t.l.c. analysis (1). The mixture is stirred with aqueous 25 per cent sodium carbonate solution (150 ml), and then extracted with benzene (3 x 40 ml CAUTION). The combined organic extracts are dried with sodium sulphate and evaporated. The residual oil is passed through a short column packed with silica gel ( 20g) and the product eluted with benzene. The eluate is evaporated and the residue purified by short path distillation under reduced pressure (Kugelrohr apparatus). [Pg.1084]

GLC uses a column packed with a solid support coated with a viscous liquid. The volatile sample is injected through a septum into an inert gas stream that evaporated the sample and carries it onto the column. Separation is achieved by differential partition of the sample components between the liquid coating and the continuously replaced gas stream. Eventually, each compound flushes off the column and into the detector in reverse order to their affinity for the column. The column is placed in a programmable oven and separation can be modified using temperature gradients. [Pg.13]

Correct sample preparation ensures good resolution and extends the life of the column. Sample buffer composition does not directly affect resolution. During separation the sample buffer is exchanged with buffer in the column. Viscous samples, which could cause an increase in back pressure and affect column packing, should be diluted. Samples must be free from particulate matter, particularly when working with bead sizes of 34pm or less (see Chapter 8 for details of sample clarification procedures)... [Pg.90]

Stopcocks are used to control the flow rate and should be wide bore to prevent plugging with viscous mobile phases. Removable bottoms are used for those separations that require long times. The bottom can be removed and the column packing pushed out with a plunger (CARE this is not as easy as it sounds). The column packing then can be sectioned, and the desired compounds extracted or washed from the inert phase for further use. [Pg.155]

Many of the potential scrubbing liquids become viscous at low temperatures and do not spread well on the column packings which are generally used for absorption. Plate columns can be used but they have a higher pressure drop for the same duty, involving more fan power to move the solvent-laden air (SLA) through the system. [Pg.11]

There are two general types of GC column packed and capillary (also known as open tubular). Packed columns contain a finely divided, inert, solid support material (commonly based on diatomaceous earth) coated with a viscous liquid stationary phase. Most packed columns are 1.5-lOm in length and have an internal diameter of 2-4mm. The original glass capillary columns had an internal diameter of a few tenths of a millimeter and were also one of two types, wall-coated open tubular (WCOT) and support-coated open tubular (SCOT). WCOT columns consist of a capillary tube whose walls are coated with liquid stationary phase. In SCOT columns the inner wall of the capillary is lined with a thin layer of support material such as diatomaceous earth, onto which the stationary phase has been adsorbed. Both of these types of capillary column provide greater separation efficiency than packed columns, but since 1979 they have... [Pg.54]

When packing of the porous materials is not sufficiently tight, repeated injection of a viscous solution leads to an increasing packing density, leaving a void space at the column inlet. When the void space was filled with extra porous materials, it was observed (1) that the resolution of HOPC decreased slightly compared with first-time use. When the column ceased to produce the void space, the separation performance became reproducible. [Pg.626]


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See also in sourсe #XX -- [ Pg.348 ]




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