Liquid chromatography (LC), defined as any chromatographic procedure in which the moving phase is a liquid (1), has proven
to be the predominant technology used in laboratories worldwide during the past 30-plus years. During this time, the field
of LC has seen many new developments, all the way from the pump to the recording of the data. Keeping pace with these technological
developments, the term LC has also morphed, at times, being referred to as high "pressure" and high "performance", high "speed,"
and "modern" LC. However, all still have their origins in the early days of LC (2,3).
With the relatively recent introduction of columns using sub-2-ľm particles, technology seems to be driving the use of the
word pressure more and more. Smaller particle sizes increase the pressure drop across the column, giving rise to what today
is called "ultra" or "very" high pressure LC, and contemporary LC component and system technology has had to adapt to take
full advantage of the increased resolution, speed, and sensitivity afforded by the drop in particle size (4,5). However, regardless
of what it is called, today's chromatography laboratory is really concerned with performance, measured as throughput, cost
per analysis, or some other metric, and if it is delivered at 1000 psi or 20,000 psi, it really doesn't matter. It is more
about what solves the problem, or provides the answer, in as efficient a way as possible. So in that context, in this inaugural
column, I'll look at an overview of some of the newer LC technology, and in future columns, I will delve into a few more specifics
concerning what constitutes the anatomy of a contemporary LC system.
System Architecture
Figure 1
Contemporary LC systems contain the same basic components as those dating back to the 1970s and 1980s: a pump, an injector,
a column, a detector, and a data-recording device. However, the way in which these components are connected and interact has
changed dramatically over the years. Contemporary LC systems can be either modular or integrated in design, and use high-pressure
or low-pressure solvent mixing. Modular systems are constructed of individual components that can be mixed and matched depending
upon the application. There are some advantages to a modular system architecture: the components can be selected based upon
need and performance (for example, the most sensitive detector for a particular application) and can be serviced easily with
minimal downtime by replacing a module in the event of a failure. However, there are some potential disadvantages to a modular
architecture: variable system volumes, system-to-system variability, multiple fluidic and data–control connections, and regulatory
issues (for example, instrument qualification when modules are changed) all need be considered. Integrated systems consist
of components, primarily the pumps and injector, that can be operated from a single control source and user interface. In
the integrated format, if one component goes down, the whole system is affected. That likelihood might be diminished over
a modular system as there is less complexity and fewer power supplies, check valves, seals, and so forth. System-to-system
variability also is diminished, as each system can be preconfigured identically at the manufacturer.
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