Venter Pieter
Biomedical Research and Innovation Platform, South African Medical Research Council, P.O. Box 19070, Tygerberg, Cape Town 7505, South Africa.
Molecules. 2025 Apr 23;30(9):1885. doi: 10.3390/molecules30091885.
This study investigates the effects of common additives, which provide distinct proton sources-ammonium (NH) and hydronium (HO)-along with their corresponding conjugate base species, on signal intensity in positive ionization mode. The findings reveal that signal intensity is influenced by factors such as solvation enthalpy, surface tension, and conductivity. At lower additive concentrations (<10 mM), based on fold changes, no clear distinction could be made between formic acid, acetic acid, and their corresponding salts. At higher additive concentrations, NH appears to be a more efficient proton source than H (HO), likely due to its more positive solvation enthalpy, which promotes greater enrichment of NH on the droplet surface, as well as the reduced surface tension of ammonium salts compared to their acid counterparts. Additionally, ammonium hydroxide proves to be the most effective ammonium-based modifier, likely due to its anionic conjugate base, hydroxide, which has a more negative solvation enthalpy compared to acetate and formate. This characteristic is hypothesized to reduce charge neutralization of cations on the droplet surface and/or in the gas phase. Furthermore, ammonium hydroxide exhibits lower conductivity compared to the other ammonium additives, which is believed to enhance signal intensity. Ammonium bicarbonate, the second most effective additive, uniquely prevents metal adduct formation, leading to enhanced [M + H] ion signals.
本研究调查了常见添加剂在正离子模式下对信号强度的影响，这些添加剂提供了不同的质子源——铵离子（NH）和水合氢离子（H₃O⁺）以及它们相应的共轭碱物种。研究结果表明，信号强度受溶剂化焓、表面张力和电导率等因素影响。在较低添加剂浓度（<10 mM）下，基于倍数变化，甲酸、乙酸及其相应盐之间无法明确区分。在较高添加剂浓度下，铵离子似乎是比氢离子（H₃O⁺）更有效的质子源，这可能是由于其具有更正的溶剂化焓，促进了铵离子在液滴表面的更大量富集，以及与相应酸相比铵盐的表面张力降低。此外，氢氧化铵被证明是最有效的基于铵的改性剂，可能是由于其阴离子共轭碱氢氧根离子，与乙酸根和甲酸根相比，其溶剂化焓更负。据推测，这一特性可减少液滴表面和/或气相中阳离子的电荷中和。此外，与其他铵添加剂相比，氢氧化铵的电导率较低，据信这会增强信号强度。碳酸氢铵是第二有效的添加剂，它独特地防止了金属加合物的形成，从而增强了[M + H]⁺离子信号。
