High Performance Liquid Chromatography by Heinz Engelhardt (auth.)

By Heinz Engelhardt (auth.)

Modern liquid column chromatography (LC) has constructed speedily because 1969 to turn into a typical approach to separation. If the statisticians are to be believed, the hot development of LC has been the main specta­ cular improvement in analytical chemistry and has now not but abated be­ reason its monstrous power for program continues to be absolutely make the most­ ed. major elements contributing to this persisted upward push are the simplicity and occasional fee of the necessary simple apparatus and the rela­ tive ease of buying and reading the information. regrettably, in LC, as so usually within the box of analytical chemistry, the on hand advertisement tools are usually way more complex - and therefore way more dear - than is nec­ essary for regimen program. Therein additionally lies the danger of propa­ gating a "black field" philosophy that may be really detrimen­ tal to chromatography. additionally, it sounds as if to were forgotten, as used to be performed formerly with gasoline chromatography, that insufficient sep­ aration via a column will be remedied in simple terms with nice hassle, if in any respect, by way of digital ability. additionally, even if the capillary columns fresh­ ly encouraged with nice enthusiasm for LC will satisfy the expecta­ tions in their proponents is very questionable except somebody comes up with a few new and innovative ideas.

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The sealing problems with small diameter pistons are relatively simple. Diaphragm pumps are recommended for chromatographic purposes because the parts that are contacted by the eluent can be readily made from inert materials such as stainless steel. In such pumps the piston movement is transmitted by means of a hydraulic fluid to the diaphragm and thence to the eluent. Because the piston seals contact only the hydraulic fluid (a specified high viscosity oil), the sealing problems are reduced and the reliability increased.

34) has a maximum at k' = 2. 5 to 4. MuUicorrrponent analyses, of course, cannot be carried out in this narrow k' range. For them, the separation efficiency must be increased at the expense of the analysis time, by either operating at a slower flow velocity or employing a longer column. For every column there is an optimum floUJ rate above which an in- crease in pressure fails to reduce the analysis time. The speed of analysis is proportional to Hlu, whereas the eluent velocity is proportional to the applied pressure.

Pumps with an electronically regulated stroke frequency (driven by stepping or DC motors) are particularly well suited for installation in gradient systems. 4. Gas-driven Displacement Pumps Gas-driven pumps, in their simplest form, consist of a plastic vessel within a pressurized chamber that is connected to a gas cylinder. In an even simpler method pressure from a gas cylinder is used to drive the eluent contained in a long tube. These pumps were used at the beginning of the development of HPLC.

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