Development of a capillary electrophoresis–mass spectrometry method for small peptides in the soil solution

Small peptides are being investigated for their role in ecosystem cycling and plant uptake of organic N, but little is known of molecular forms in the soil solution. The aim of this study was to develop a capillary electrophoresis–tandem mass spectrometry procedure for profiling small peptides in the soil solution. Capillary electrophoresis–mass spectrometry was capable of separating and detecting a range of small peptide standards. Adequate recovery (>90%) of standard peptides spiked into samples of soil solution indicated that separation and detection were robust and not significantly affected by the sample matrix. The method was applied to samples of soil solution from grassland mesocosms filled with clay-loam soil from an abruptic lixisol. Soil solution (ultrafiltered <3 kDa) contained at least 298 putatively identified peptides with most being smaller than 600 Da. Less than 5% of small peptides contained basic amino acids, which may reflect their preferential adsorption to the soil stationary phase versus peptides comprised of acid or neutral amino acids. Capillary electrophoresis–mass spectrometry of small peptides is robust and has already yielded novel findings with its first proof of concept measurements on the soil solution.