Page 375 - Multidimensional Chromatography

366 Multidimensional Chromatography

Figure 13.17 LC–GC–MS(EI) chromatogram of a treated drinking water containing 55
1
and 40 ng l , respectively, of DBP and DEHP. Reprinted from Journal of High Resolution
Chromatography, 20,T. Hyötyläinen et al., ‘Reversed phase HPLC coupled on-line to GC by
the vaporizer/precolumn solvent split gas discharge interface; analysis of phthalates in water’,
pp. 410–416, 1997, with permission from Wiley-VCH.

surfaces and solvent trapping can not be used to improve the retention of volatile
solutes. The experimental conditions for this analysis are shown in Table 13.2. This
study has demonstrated that column temperature during transfer is a very important
parameter which depends to a large extent on the volatility of the compounds and the
composition of the mobile phase. However, problems with volatile solutes can still
be significant.
For the LC separation, 10 ml of sample was injected through a loop. The LC flow-
rate was 1000 l min 1 and at the end of the enrichment process this was reduced to
1
100 l min . The mobile phase composition was optimized to eliminate matrix
polar compounds and elute the phthalates in a small fraction.
Figure 13.17 shows the LC–GC–MS chromatogram of treated drinking water
containing 55 and 40 ng l 1 of di-n-butylpthalate (DBP) and di(2-ethylhexyl)phtha-
late (DEHP), respectively. The PTV system therefore allows the LC eluent to be
injected directly and no change in the composition is needed.
However, the most frequently used system is trace enrichment in a short LC col-
umn or SPE precolumn. The column is usually filled with C 18 or PLRP-S and dried
with nitrogen prior to elution. The analytes are eluted with an organic solvent, usu-
ally ethyl acetate, which is injected into the gas chromatograph through an on-
column interface by a retention gap. In the chromatograph there is also a retaining
precolumn, to minimize losses of the most volatile compounds, an analytical column
and, between the precolumn and the analytical column, a solvent vapour exit (SVE)
to eliminate the vapour (Figure 13.18).