The Basics

In the previous column, we introduced chromatography, a powerful separation technique that typically involves partitioning of mixtures between an adsorbent stationary phase and a liquid or gas mobile phase. Separation of mixtures of contaminates, without contaminant modification, is important for accurate quantification and identification. In the context of contamination control, we concentrate on chromatography for separation and identification; chromatography can also be used to purify product.

In liquid-solid column chromatography, the mixture is applied to a column packed with sorbent. The mixture is separated by washing or eluting the columnwith one or more solvents (in this context solvent could include water).

Complex Chromatography Systems

Current chromatography systems employ the same basic principles as did the nearly century-old systems but they can be extremely sophisticated and therefore extremely daunting. In current analytical systems, the humble chromatography column is hidden in one or more attractive but uninformative “black boxes” (or grey or blue boxes) that are typical of what you might have seen on a visit to an analytical laboratory. The column is augmented by a number of assistive devices. A system typically contains a sample injection device, eluting material(s) with a pump, perhaps a gradient maker, and a chromatography column packed with sorbent. The eluent may be a single chemical, a mixture, a sequence of chemicals, or a gradient. In a gradient, the relative concentrations of elution chemicals are gradually changed. The sorbent (the stationary phase packed into the column) and the length of column are specific to the application in question. Rather than visually observing the bands, the separated materials are analytically “visualized” and quantifiedusing an appropriate detector along with data analysis software.

Between the column and the detector there may be a device for post-column modification of the eluted bands. This modification can include ion exchange or a more complex chemical reaction to enhance the level of detection. In addition, there is usually a small “guard” column to protect the main analytical column from gross (and hopefully irrelevant) residue; and if many samples are to be separated and detected at once there can be a turntable with an auto-sampling device.

There is no need to be intimidated by all the bells and whistles; at the heartof it all, is the basic chromatography column, separating complex mixtures.