The modern HPLC pump

A discernible trend in modem pump design is towards the use of very small pistons (stroke volume around 100 pi). These tiny pistons have to be operated at very high driving speeds, to provide the flow rates required in analytical HPLC. However, when they are used in combination with electronic feedback pulse control mechanisms, as described above, they can provide extremely stable solvent delivery characteristics. Such is the efficacy of this approach that single piston pumps designed in this way are able to easily out-perform older dual piston pumps, and are consequently beginning to account for a major part of the LC pump market. 

Many manufacturers have used the capabilities of on-board processing power to provide a user friendly interface for the operator. This results in a host of useful (and some not so useful) features for the analyst, and allows the pump to be remotely controlled by a computer, or another component of the HPLC system. This can facilitate method development for instance, as the pump can be programmed to change automatically the composition of the mobile phase after a number of runs. It does this by changing the proportion of time that it draws from each of a number (up to four) of solvent reservoirs, that can contain diflferent modifiers or buffers. Computerisation of pumps can also allow unattended runs to be performed with a greatly increased measure of confidence. In a networked 

Many modern pumps have in-built electronic logs and diagnostic systems, which remind the operator when a routine maintenance procedure is due, or inform that a certain component is performing outside tolerance levels. The offending part may then be replaced before it has a chance to fail completely at some later, and much more inconvenient, time. 

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