Page 76 - Illustrated Pocket Dictionary of Chromatography

72 EXTRACOLUMN VOLUME

extracolumn volume Any volume in the system from the injec-
tor to the detector (inclusive) is extracolumn volume. Extracolumn
volume decreases the overall efficiency of a separation because each
source adds to the total variance (i.e., width) of a peak. These volumes
should be kept to a minimum by using the narrowest appropriate inner
diameter connecting tubing, shortest lengths of connecting tubing,
smallest detector cell volume, zero-dead volume unions, etc.

extrapolation The process of extending a curve beyond an estab-
lished set of data points. For extrapolated results to be of analytical
value a number of assumptions are made: (1) The mathematical rep-
resentation of the data does not change past the data set used to gen-
erate it; (2) the chemical nature of the analyte does not change; (3)
the detector responds in the same fashion; (4) the sources of error are
equal to or less than that found within the bounds of the data set.

Working outside the defined working curve as defined by known standards
(extrapolation) is dangerous because there is no guarantee of linearity (or confor-
mance to any other best-fit parameter). Interpolation always gives the most reli-
able result.