A new method for the rapid analysis of 1H-Pyrrole-2,5-diones (maleimides) in environmental samples by two-dimensional gas chromatography time-of-flight mass spectrometry

Maleimides (1H-Pyrrole-2,5-diones) are monopyrrolic pigment derivatives with
specific alkyl side chains that can be directly linked to their tetrapyrrole
precursors, most notably chlorophylls and bacteriochlorophylls. These
compounds can be used as palaeoenvironmental indicators such as, for
instance, algal productivity and redox conditions in ancient and modern aquatic
systems. Here, we present a new method using two-dimensional gas
chromatography time-of-flight mass spectrometry (GC×GC-ToF-MS), which
enables the rapid analysis of maleimides in complex mixtures and different
matrices (e.g. sediments and soils), therefore largely simplifying the previous
intricate maleimide purification protocol. This method also reduces the potential
for bias associated with partial losses due to low recovery and the high volatility
of maleimides. The maleimide distributions and concentrations obtained by
GC×GC-ToF-MS were reproducible and in agreement with the previously used
purification procedure followed by analysis with traditional gas chromatography - mass spectrometry (GC-MS). The new method also resolved previously
unrecognised, partial coelution of some maleimides with unknown compounds
by quantification with the m/z 75 fragment ion. Furthermore, the higher
sensitivity enabled the detection of previously unrecognised and preliminarily
identified maleimides based on their relative retention times. The new, easier,
rapid and more sensitive GC×GC-ToF-MS method greatly facilitates the
analysis of maleimides in environmental samples to study tetrapyrrole
degradation processes and will further the development of maleimides as
biomarkers for palaeoenvironmental reconstructions.