Enhancing the power of liquid chromatography-mass spectrometry-based urine metabolomics in negative ion mode by optimization of the additive.
Untargeted liquid chromatography-mass spectrometry (LC-MS)-based metabolomics studies are usually carried out in both positive and negative ion modes; however, it is frequently ignored that the optimal conditions in positive ion mode and negative ion mode are often not the same. We carried out a systematic investigation on urine samples to evaluate the additive effects in negative ion mode. It was found that the widely used conditions, 0.1% formic acid (FA) and NH(4)Ac at different pH, are far from the optimum for untargeted urine metabolomics studies. Compared to 0.1% FA, the use of 1 mM acetic acid (HAc) resulted in almost three times as many detected peaks (401 vs 148) and around five times the size of the peak area (33.55 × 10(6) vs 6.47 × 10(6)). The remarkable improvement can be explained by two factors: (i) a significantly enhanced ionization efficiency due to the combination of an appropriate pH at around 4.0-4.5, the reducibility of H(+), and the high gas-phase basicity of Ac(-) and (ii) a reproducible LC separation due to an acceptable buffering capacity. Our study revealed the importance and necessity of additive optimization, which can be of benefit in related metabolomics studies.
Department of Food Science, Aarhus University, Aarslev, Denmark.
Xumin
X
Zhang
Morten Rahr
MR
Clausen
Xiaolu
X
Zhao
Hong
H
Zheng
Hanne Christine
HC
Bertram
D000085:Acetates / Q000737:chemistry; D019342:Acetic Acid / Q000737:chemistry; D000596:Amino Acids / Q000652:urine; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005561:Formates / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D055432:Metabolomics; D051379:Mice; D021241:Spectrometry, Mass, Electrospray Ionization; D014867:Water / Q000737:chemistry
D000085:Acetates; D000596:Amino Acids; D005561:Formates; D007477:Ions; D014867:Water; C030544:formic acid; D019342:Acetic Acid; C018824:ammonium acetate