The term chlorophyll c encompasses a small but heterogeneous group of algal pigments, characterized for being porphyrins rather than chlorins.
Chlorophylls c are in fact protochlorophyllides, with a fully unsaturated ring D, that differ in their peripheral substituents. Particularly important is the substituent at C-17, that can be either a propionic or an acrylic acid residue. This substituent can remain as a free carboxylic acid or be esterified to a galactolipid residue. Chlorophylls c are distributed within algal classes with different degrees of specificity, which allows their use as chemotaxonomic biomarkers in oceanographic studies. Mass spectrometry has been linked to the structural elucidation of chlorophylls c and most of them have been detected and characterized in parallel with the development of soft ionization techniques. In this article we review the application of direct and tandem mass spectrometry techniques to the analysis of acidic and esterified chlorophylls c, summarize their fragmentation patterns and enumerate some experimental fragmentation rules for their identification.