title: Robust analysis of underivatized free amino acids in soil by hydrophilic interaction liquid chromatography coupled with electrospray tandem mass spectrometry.
abstract: Amino acids are an important and highly dynamic fraction of organic N in soils and their determination in soil without derivatization is challenging due to the difficulties in separation and detection of trace amounts of these polar analytes. In the present work, we developed an analytical method to quantify 20 free amino acids in aqueous soil extracts without derivatization. The method employed hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) technique combined with a cation exchange solid phase extraction (SPE). Four stable isotope labelled amino acids were used as internal standards to improve the method performance. Good separation of 20 underivatized amino acids was achieved within 12min. The limit of detection (LODs) and limit of quantification (LOQs) were in the range of 13-384ngg(-1) and 43-1267ngg(-1) (dry soil basis), respectively. The results showed that overall recoveries with high precision were obtained for the extracted free amino acids from ten different soils. The overall recoveries of 18 amino acids were similar for the ten soils used, which differed substantially in organic C content and in other properties as soil texture and pH. For most of the amino acids, the average recoveries from soil extracts were between 74% and 117%, with the exception of Met (31%), Pro (52%) and Arg (68%). Variability was within acceptable limits (relative standard deviations were between 4% and 13%), with the exception of Met (relative standard deviation=90%) and Arg (relative standard deviation=53%). Thus the proposed method with high throughout and high analyte specificity shows great promise for consistent analysis of free amino acids extracted from soils and offers new horizons for the analysis of amino acids in terrestrial and aquatic ecosystem.
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH Amsterdam, The Netherlands. Electronic address: J.Gao@uva.nl.
authors.forename: Jiajia
authors.initials: J
authors.lastname: Gao
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Rick
authors.initials: R
authors.lastname: Helmus
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Chiara
authors.initials: C
authors.lastname: Cerli
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Boris
authors.initials: B
authors.lastname: Jansen
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Xiang
authors.initials: X
authors.lastname: Wang
authors.affiliation: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Earth Surface Science, Science Park 904, 1098 XH Amsterdam, The Netherlands; Dresden University of Technology, Soil Resources and Land Use, Pienner Strasse 19, D-01737 Tharandt, Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Kalbitz
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D002853:Chromatography, Liquid / Q000379:methods; D057927:Hydrophobic and Hydrophilic Interactions; D057230:Limit of Detection; D012987:Soil / Q000737:chemistry*; D052616:Solid Phase Extraction / Q000379:methods; D012997:Solvents; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods; D014867:Water
chemical_list: D000596:Amino Acids; D012987:Soil; D012997:Solvents; D014867:Water
keywords: Hydrophilic interaction LC; Optimization; Soil amino acids; Solid phase extraction; Tandem MS