Page 359 - Multidimensional Chromatography

350 Multidimensional Chromatography

Figure 13.7 Selectivity effected by employing different step gradients in the coupled-
column RPLC analysis of a surface water containing 0.40 g l 1 bentazone, by using direct
sample injection (2.00 ml). Clean-up volumes, (a), (c) and (d) 4.65 ml of M-1, and (b) 3.75 ml
of M-1: transfer volumes, (a), (c) and (d), 0.50 ml of M-1, and (b), 0.40 ml of M-1. The
displayed chromatograms start after clean-up on the first column. Reprinted from Journal
of Chromatography, A 644, E. A. Hogendoorn et al., ‘Coupled-column reversed-phase liquid
chromatography-UV analyser for the determination of polar pesticides in water’,
pp. 307–314, copyright 1993, with permission from Elsevier Science.

The experimental conditions are shown in Table 13.1, while Figure 13.9 shows
the chromatogram of a soil sample extract spiked with fenpropimorph obtained by
this method, plus the chromatogram from the two columns connected in series with-
out column switching.
In multiresidue analysis, where more analytes with a wide polarity range need to
be determined, large transfer volumes are required, and consequently, the selectivity
is lower. However, since the major interferences in water analysis are the polar
humic and fulvic acids, removing this early eluting interference in coupled-column
RPLC will also be feasible in multiresidue methodology.
Several examples have been described in the literature, and some of these are
included in Table 13.1.
For instance, a group of triazine herbicides has been determined in environmen-
tal water samples. In this example (33), a group of four triazines (simazine,
atrazine, terbuthylazine and terbutryn) were determined by LC–LC by using the
experimental conditions specified in Table 13.1. The flow-rate was 1 ml min 1 in
both cases. The total analysis time was only 7 min, which enables a sample
throughput of up to 60 samples per day. However, the limits of detection from this
1
system were only about 0.1–0.15 g l , which is not enough for drinking water
according to EEC regulations. These authors proposed a solid-phase extraction step