Page 364 - Multidimensional Chromatography

Multidimensional Chromatography in Environmental Analysis 355

Figure 13.11 Column-switching RPLC trace of a surface water sample spiked with eight
chlorophenoxyacid herbicides at the 0.5 g l 1 level: 1, 2,4-dichlorophenoxyacetic acid;
2, 4-chloro-2-methylphenoxyacetic acid; 3, 2-(2,4-dichlorophenoxy) propanoic acid; 4, 2-
(4-chloro-2-methylphenoxy) propanoic acid; 5, 2,4,5-trichlorophenoxyacetic acid; 6, 4-(2,4-
dichlorophenoxy) butanoic acid; 7, 4-(4-chloro-2-methylphenoxy) butanoic acid; 8, 2-(2,4,5-
trichlorophenoxy) propionic acid. Reprinted from Analytica Chimica Acta, 283, J. V.
Sancho-Llopis et al., ‘Rapid method for the determination of eight chlorophenoxy acid
residues in environmental water samples using off-line solid-phase extraction and on-line
selective precolumn switching’, pp. 287–296, copyright 1993, with permission from Elsevier
Science.

coupled-columns, the sensitivity and selectivity are both higher because interfering
peaks do not enter the second column. This is demonstrated in Figure 13.12, which
shows the chromatograms obtained both with and without column switching. The
experimental conditions are reported in Table 13.1. As can be seen from this figure,
there are significant differences in the selectivity and sensitivity for the two chro-
matograms, which again demonstrates the suitability of RPLC–RPLC methodology.
The coupling of low-resolution liquid chromatography (or SPE) to liquid chro-
matography has been widely applied to environmental analysis because of the
improvement in sensitivity.