Page 265 - Multidimensional Chromatography

260 Multidimensional Chromatography

by coupling RPLC and ion-exchange LC. After ultrafiltration of the blood sample,
400 l of the ultrafiltrate was injected into an LC–LC system (Figure 11.1(a)) with-
out further pretreatment. A heart-cut (ca. 1 ml) of the eluate of the first column
(octadecylsilica (ODS)) which contained the sameridine, was transferred to and
enriched on, a cation-exchange extraction column. In the next step, the concentrated
sample was desorbed into the second analytical column (cation-exchange) for the
final separation and subsequent UV detection at 205 nm. In this way the interfer-
ence-free and sensitive determination of sameridine could be achieved (Figures
11.1(b) and (c)) with a limit of quantitation (LOQ) of 1 nM and a within-day preci-
sion of 2–8 %. In a similar approach, Baker et al. (18) determined the major

Figure 11.1 (a) Schematic representation of a coupled-column LC system for sameridine
analysis consisting of a reversed-phase analytical column (C1), a cation-exchange extraction
column (C2) and a cation-exchange analytical column (C3); (b) chromatogram of plasma
sample after intrathecal administration of sameridine (plasma concentration, 11.2 nM); (c)
chromatogram of a blank plasma sample. Reprinted from Journal of Chromatography, B 708,
E. Eklund et al. ‘Determination of free concentration of sameridine in blood plasma by
uttrafiltration and coupled-column liquid chromatography,’ pp. 195–200, copyright 1998,
with permission from Elsevier Science.