Page 293 - Multidimensional Chromatography
P. 293
288 Multidimensional Chromatography
Figure 11.18 Schematic diagram of an in-line SPE unit for CE using (a) polyester wool
frits to hold the sorbent, or (b) a particle-loaded membrane. Reprinted from Journal of
Capillary Electrophoresis, 2, A. J. Tomlinson and S. Naylor, ‘Enhanced performance mem-
brane preconcentration–capillary electrophoresis–mass spectrometry (mPC–CE–MS) in
conjunction with transient isotachophoresis for analysis of peptide mixtures,’ pp 225–233,
1995, with permission from ISC Technical Publications Inc.
interferences can also be expected when biological fluids are injected directly, since
in an in-line set-up the complete sample passes both the micro-unit and the CE cap-
illary.
The use of SPME for CE has not (yet) been studied widely. Li and Weber (170)
reported an off-line SPME–CE approach for the determination of barbiturates in
urine and serum, utilizing a sorbent of plasticized PVC coated around a stainless
steel rod. For extraction, the coated rod was inserted for 4 min in a Teflon tube con-
taining 50 l of sample, and next the rod was repeatedly desorbed in another Teflon
tube which each time contained 5 l of desorption solution. This solution was trans-
ferred to an injection vial and an aliquot was injected into the CE system (Figure
11.19). The extraction procedure appeared to be selective and effectively allowed the
handling of very small samples.