ABSTRACT
As its name implies, this important analytical technique combines two separate procedures: liquid chromatography (LC) and mass spectrometry (MS). Both individual techniques are quite old. LC developed as a means of separating nonvolatile mixtures into their component substances and provided a big step forward in revealing their complexities and analyzing them. The method is described fully in Chapter 35, but it can be summarized as follows (Figure 37.1): by passing a mixture in a liquid stream (the mobile or liquid phase) through a long column packed with a stationary phase (particles of a special solid), the components of the mixture become separated and emerge (elute) one after another from the end of the column. In a simple LC instrument, the emerging components dissolved in the liquid mobile phase are measured by passing the liquid stream through either an ultraviolet (UV) or a refractive-index detector. The detected components are recorded as peaks on a chart (the liquid chromatogram). The area of a peak correlates with the amount of a component, and the time taken to pass through the column (the retention time, i.e., the time to the peak maximum) gives some information on the possible identity of the component. However, the identification is seldom absolutely certain and is often either vague or impossible to determine.
