Figure 12.1
Outline procedures for analysis of an
organic material.and/or contaminated ('dirty') sample is to be analysed, a clean-up procedure is often employed before
determination of the analyte(s). This is designed to avoid interference by other components of the
sample, i.e. the matrix, and is particularly desirable prior to a gas or liquid chromatographic separation
as the quality of the chromatography can be greatly improved and the working life of the column
extended. Solid phase extraction (SPE) has recently become particularly important in this context
(section 4.2).
Another concentration technique similar in principle to supercritical fluid chromatography, SFC (p.
150) is supercritical fluid extraction, SFE. Requiring more expensive equipment than solid phase
extraction, it involves pumping carbon dioxide under supercritical conditions (above 31.1°C and 72.9
bar or 1050 psi) through an extraction chamber containing the sample. The extracted analytes are either
collected in a suitable solvent prior to analysis or passed directly into a gas, liquid or supercritical
chromatograph. SFE is fast, efficient and capable of concentrating trace constituents from a wide range
of materials and manufactured products.