Page 266 - Multidimensional Chromatography

Biomedical and Pharmaceutical Applications 261

metabolite of the glucocorticoid tipredane in rat urine which was injected directly
into the first LC column. In this case, the initial separation was performed on a
cyanopropylsilica column and a portion of the eluate was switched to an ODS col-
umn where the final separation was carried out. This method allowed quantification
of the metabolite down to 25 ng/ml, showed acceptable linearity, precision and accu-
racy in the 25–5000 ng/ml range, and was successfully used for a long-term toxi-
cology study. Lanbeck-Vallén et al. (28) used post-column derivatization with fluo-
rescamine for the analysis of the penicillin ampicillin in plasma by LC with fluores-
cence detection. However, since fluorescamine reacts with most primary amines, the
selectivity of the LC system had to be increased. This was achieved by the use of a
coupled column system (Figure 11.2(a)). The total combination yielded a highly
selective system which permitted the sensitive determination of ampicillin (Figure
11.2(b)) with a detection limit of 14 nM for 0.5 ml plasma samples.

Figure 11.2 (a) LC–LC system with post-column reaction detection for the determination
of ampicillin in plasma; (b) Chromatogram of plasma sample (collected 10 min after oral
administration of 670 mol of ampicillin) containing 1.26 M ampicillin (amp). Reprinted
from Journal of Chromatography, 567, K. Lanbeck-Vallén et al., ‘Determination of ampicillin
in biological fluids by coupled-column liquid chromatography and post-column derivatiza-
tion,’ pp. 121–128, copyright 1991, with permission from Elsevier Science.