TABLE OF CONTENTS Important progress has been achieved in the development of methods to analyse proanthocyanidins and tannin-like compounds in complex mixtures. Although classical proanthocyanidin reagents such as Porter's reagent, vanillin or DMCA can still be of use for the detection of proanthocyanidins in plant samples and/or for comparison of samples of identical composition, they appear rather inaccurate for characterization and quantification purposes. Determination of average composition should be based on NMR spectrometry and/or depolymerization in the presence of nucleophilic agents followed by HPLC analysis. Both types of method also give access to calculations of mDP values. However, application of the former to higher polymers is limited by poor integration of signals corresponding to end units, due to higher noise to signal ratios as the molecular weight increases. The latter methods appear more sensitive but require time-consuming purification of each released unit, for identification and calibration. Information on mass distribution can theoretically be obtained by gel permeation and mass spectrometry. However, the lack of appropriate standards to calibrate or validate these methods, due to poor resolution of separation techniques for higher molecular weight and/or highly polydisperse compounds, remains a major problem. Besides, difficulties in ionizing higher molecular weight proanthocyanidins (in MALDI-TOF) or in the interpretation of complex and overlapping signals contributed by multiply charged ions (in ESI-MS) has so far impeded accurate analysis of polymeric fractions.
