The main problem in the analysis of low molecular mass flavan-
3-ols of crude grape seed extracts by HPLC with direct injection is
their separation. This is essentially due to the close chemical
structures of these compounds, which generally leads to peak
overlapping. In addition, the presence of high molecular mass
procyanidin polymers and complexes which elute under the
resolved peaks as ‘‘baseline drift or hump’’ increases the detection
background to levels that make the determination of even resolved
peaks impossible. Fig. 1 shows the HPLC profile (detected at
280 nm) of the whole grape seed extract (GSE-W) obtained by the
fast elution method (45 min) (the upper trace). This method does
not pursue fine separation of the sample components. Rather, it
gives their profile at decreasing order of polarities and is very
useful in the appreciation of the non-separable polymeric and
complex constituents. Under these conditions of elution, it is easy
to appreciate how the UF clean-up diminished the ‘‘background
hump’’ progressively with the decrease of the membrane
molecular mass cut off (MMCO) to levels close to the normal
baseline, as in the case of the 10 kDa MMCO membrane permeate
(GSE-UF10) (Fig. 1) (81% reduction of the chromatographic area
corresponding to the background hump (min 5 and 38).