The columns

Unlike other modes of high-performance liquid chromatography (HPLC), separation efficiency comes only from the stationary phase, while the mobile phase should have no effect. The whole separation occurs within the volume of the pores, which typically equals approximately 40% of the total column volume. This means, that long columns, or often sets of several columns are required. Different types of SEC columns are available, which are either based on porous silica or on semi-rigid (highly cross-linked) organic gels, in most cases copolymers of styrene (St) and divinylben-zene (DVB).

Table 1 lists some commercially available column packings for nonaqueous SEC. In general, silica-based packings are quite rugged, while organic packings must be handled with care. Typically, the separation range of a column covers approximately two decades of molar mass (e.g. from 1 x 104 to 1 x 106). Most producers also offer mixed bed columns covering a much wider range.

Obviously, a good separation is only one part of a good analysis. Another crucial point is the detection of the fractionated sample leaving the column.

At least one concentration-sensitive detector has to be used in an SEC system. In the analysis of copolymers, a second concentration-sensitive detector is required, the sensitivity of which towards the components of the polymer differs from that of the first detector.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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