Page 45 - Multidimensional Chromatography

Coupled HPLC with HRGC 35

2.5.2 LIQUID–LIQUID EXTRACTION

This method relies on the on-line extraction of an organic compound from an aque-
ous sample by using an organic solvent. In automated liquid–liquid extraction
(LLE), the solvent (organic) is injected via a small segmentor into the water sample,
which flows through a small-diameter fused silica tube. Phase separation is achieved
by using a semipermeable PTFE membrane (34–36) or a sandwich-type phase sepa-
rator. For the first case (34), the configuration adopted is illustrated in Figure 2.14.
The water sample was delivered by either an HPLC pump, syringe or a pressurized
flask, and then extracted with n-pentane. Separation of the two phases was achieved
by using a membrane separator (Figure 2.15), based on a semipermeable PTFE
membrane, which has different wetting characteristic for the phases. This system
was used to analyse volatile organic trace compounds, as shown in Figure 2.16
where a water sample was spiked with 200 ppb of a naphtha fraction (34).

Figure 2.14 Schematic representation of the set-up used for continuous flow extraction with
on-line capillary GC: (A) 1 and 4 HPLC pumps; 2, syringe pump; 3, pressurized flask with
water sample; 5, segmentor; 6, fused-silica capillary tube; 7, phase separator; 8, needle valve;
9, six-port valve; 10, sample loop; 11, empty precolumn; 12, GC column; 13, GC oven; 14,
recorder/integrator; A, water sample; B, pressurized nitrogen, C, extracted water; D, extracted
drain; E, carrier gas: (B) I, sample; O, sample drain; W, clean water stream; S, segmentor.
Reprinted from Journal of Chromatography, A 330, J. Roeraade, ‘Automated monitoring of
organic trace components in water. I. Continuous flow extraction together with on-line capil-
lary gas chromatography’, pp. 263–274, copyright 1985, with permission from Elsevier
Science.