ORIGINAL PAPER Comprehensive study of condensed tannins by ESI mass spectrometry: average degree of polymerisation and polymer distribution determination from mass spectra Laetitia Mouls & Jean-Paul Mazauric & Nicolas Sommerer & Hélène Fulcrand & Gérard Mazerolles Received: 29 October 2010 / Revised: 28 January 2011 / Accepted: 31 January 2011 / Published online: 26 February 2011 # Springer-Verlag 2011 Abstract The determination of the molecular mass distri- bution of tannins is still a challenge. To elucidate it, mass spectrometry is potentially interesting, but many previous studies have highlighted that the mass spectra of a tannin fraction do not always reflect the actual abundance of different chain lengths. To clarify the potentialities offered by the MS approach, a comprehensive study involving different tannin fractions analysed under different condi- tions was conducted with an electrospray ionization (ESI) source. This study allowed optimised ESI-MS conditions to be established for analysing tannins but also it outlines the limits of detection encountered. If the detection of high molecular weight tannins seems difficult or even impossi- ble, the spectral distortions brought about by this limitation are not totally related to the sole average degree of polymerisation of the tannin fraction studied but greatly depend on its polymer distribution. However, ESI-MS used under optimised conditions is a suitable method to study tannin composition of vegetable extracts which contain degree of polymerisations below 26. Keywords Tannins . Polyphenols . Electrospray ionisation– mass spectrometry (ESI-MS) . Degree of polymerisation . Polymer distribution . Chemometrics Introduction Interest in the characterization of condensed tannins has increased in the last few decades. These phenolic compounds are oligomers and polymers of flavan-3-ols that belong to the flavonoid class of polyphenols widely distributed in the plant kingdom. Tannin composition may differ by the nature and the number of constitutive units [1], by the type (B or A) and location of interflavanic linkages connecting the monomeric units (mostly C4–C8 and rarely C4–C6) and lastly by the conformation (linear versus branched) of polymers [2]. All theses parameters are believed to be genetically controlled because they vary with plant species, and within a given species, with plant tissue, organ and physiological stage. The study of this class of compounds in the context of their biological, nutritional and sensory properties [3–7] is particularly interesting with respect to their degree of polymerisation and how far it can influence their properties. Thiolysis and phloroglucinolysis [8, 9] of a tannin fraction are currently the methods most used to provide an average composition in terms of the nature of the constitutive units of tannins, their relative proportions and an estimate of the average degree of polymerisation (aDP). These depolymerisation methods are difficult to implement and do not give information about the polymer distribution of a tannin fraction because all the polymers contained in the Electronic supplementary material The online version of this article (doi:10.1007/s00216-011-4751-7) contains supplementary material, which is available to authorized users. L. Mouls : J.-P. Mazauric : N. Sommerer : H. Fulcrand : G. Mazerolles INRA, UMR1083, 34060 Montpellier, France L. Mouls : J.-P. Mazauric : N. Sommerer : H. Fulcrand : G. Mazerolles Montpellier SupAgro, UMR1083, 34060 Montpellier, France L. Mouls (*) : J.-P. Mazauric : N. Sommerer : H. Fulcrand : G. Mazerolles Université Montpellier I, UMR1083, 34060 Montpellier, France e-mail: moulsl@supagro.inra.fr Anal Bioanal Chem (2011) 400:613–623 DOI 10.1007/s00216-011-4751-7