Page 377 - Multidimensional Chromatography

368 Multidimensional Chromatography

Figure 13.19 Chromatograms obtained by on-line SPE–GC–MS(SIM) of: (a) 10 ml of tap
1
water spiked with pesticides at levels of 0.1 ng l ; (b) 10 ml of a sample of unspiked tap
water. Peak identification for (a) is as follows: 1, molinate; 2, -HCH; 3, dimethoate; 4,
simazine; 5, atrazine; 6, -HCH; 7, -HCH; 8, heptachlor; 9, ametryn; 10, prometryn; 11, fen-
itrothion; 12, aldrin; 13, malathion; 14, endo-heptachlor; 15, -endosulfan; 16, tetrachlor-
vinphos; 17, dieldrin. Reprinted from Journal of Chromatography, A 818, E. Pocurull et al.,
‘On-line coupling of solid-phase extraction to gas chromatography with mass spectrometric
detection to determine pesticides in water’, pp. 85–93, copyright 1998, with permission from
Elsevier Science.

micropollutants (94, 103) although such coupling is rather difficult to achieve. In
order to remove these difficulties, the cartridge that contained the immobilized anti-
bodies was coupled to the GC unit via a reverse-phase cartridge (PLRP-S) in the
determination of s-triazines (94). After enrichment of the analytes on the
immunoaffinity cartridge, they were desorbed and recollected on the PLRP-S car-
tridge by using an acidic buffer. The PLRP-S cartridge was then cleaned and dried
with nitrogen. Finally, the desorption and transfer steps were carried out with ethyl
acetate via an on-column interface.
The high selectivity of this system is demonstrated in Figure 13.20, which shows
that a non-selective FID could be used to detect triazines in complex matrices, and
1
that with 10 ml of sample the detection limits were 15–25 ng l . The experimental
conditions are shown in Table 13.2.
The on-column interface is the one which is most often used in LC–GC of aque-
ous samples because it can be applied to a wider range of compounds.The loop-type
interface is limited for determining volatile compounds that are volatilized together
with the solvent and not retained in the retention gap. Several attempts at solving this
problem have been made. One option is to add a co-solvent which enters the reten-
tion gap before the analytes and thus forms a co-solvent film in front of the eluate.