Department of Food Science, Aarhus University, Aarslev, Denmark.
Anal Chem. 2012 Sep 18;84(18):7785-92. doi: 10.1021/ac3013835. Epub 2012 Aug 24.
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.
非靶向液相色谱-质谱（LC-MS）代谢组学研究通常在正离子模式和负离子模式下进行；然而，人们经常忽略的是，正离子模式和负离子模式的最佳条件通常并不相同。我们对尿样进行了系统研究，以评估负离子模式下的附加效应。结果发现，广泛使用的条件，即不同 pH 值下的 0.1%甲酸（FA）和 NH4Ac，远非非靶向尿代谢组学研究的最佳条件。与 0.1% FA 相比，使用 1 mM 乙酸（HAc）可检测到的峰数增加近三倍（401 对 148），峰面积增加约五倍（33.55×106对 6.47×106）。这种显著的改善可以用两个因素来解释：（i）由于 pH 值在 4.0-4.5 左右，H+的还原能力，以及 Ac-的高气相碱性，组合形成了适当的 pH 值，从而显著提高了电离效率；（ii）由于缓冲能力可接受，实现了可重现的 LC 分离。我们的研究揭示了加和优化的重要性和必要性，这将有益于相关代谢组学研究。
