Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples

Natural dissolved organic matter
(DOM) is an ultracomplex mixture
that is essential to global carbon cycling but is poorly understood
because of its complexity. The most powerful tool for the DOM characterization
is high-resolution mass spectrometry (HRMS) generally combined to
direct infusion (DI) as sample introduction. Liquid chromatography
(LC) represents a compelling alternative to DI; however, state-of-the-art
techniques involve only offline LC-HRMS approaches, which have important
logistical drawbacks that make DOM analysis more challenging. This
study introduces a new method based on online coupling of liquid chromatography
to high resolution mass spectrometry, able to overcome the disadvantages
of usual approaches. It is characterized by high reproducibility (%
Bray–Curtis dissimilarity among replicates ≈ 2.5%),
and it reduces transient complexity and contaminant interferences,
thus increasing the signal-to-noise ratio (S/N), leading to the identification of an overall larger number
of formulas in the mixture. Moreover, the application of an in silico
fractionation prior to the statistical analysis allows an easy, flexible,
fast, and detailed comparison of DOM samples from a variety of sources
with a single chromatographic run.