Chromatographs and accessories

The rapid development of HPLC is attributed to the fact that many analysts regard this technique as an alternative to GC or as a means of analysis when GC cannot be used. The poor volatility or thermal instability of many compounds renders GC unsuitable for analysis and makes HPLC an attractive second choice. This is particularly evident in the pharmaceutical industry. As a result, an increasing number of manufacturers is entering the area of HPLC. In this section, the major operating principles involved in most of the 

HPLC pumps may be divided into two classes constant pressure and constant flow. 

Detailed reviews of solvent delivery systems and their operation have appeared in the literature [2-4]. In the following paragraphs, the main features of some of the more common pumping systems are discussed. 

The Altex liquid chromatograph (Fig.3.29) utilizes a dual piston approach similar to that in the Waters ALC 200 instrument. The pistons are 180° out of phase. The special cam shape results in a steady flow which is interrupted by minor fluctuations. These are damped by a flow-feedback system which is incorporated into the pump. This system has been rated at a pressure of 7000 p.s.i. 

The Micromeritics 7000 liquid chromatograph (Fig.3.30) also uses a reciprocating pumping system. The pump has several unique features. It delivers pulseless flow without a pulse damper, it can operate from an unlimited reservoir, it requires only a single pump for gradient elution and it is capable of operating at constant pressure or constant flow-rate. 

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