Fernández-Maestre Roberto, Wu Ching, Hill Herbert H
Department of Chemistry, Washington State University, Pullman, WA 9914, USA.
Int J Mass Spectrom. 2010 Dec 1;298(1-3):2-9. doi: 10.1016/j.ijms.2010.08.009.
The mobilities of a set of common α-amino acids, four tetraalkylammonium ions, 2,4-dimethyl pyridine (2,4-lutidine), 2,6-di-tert-butyl pyridine (DTBP), and valinol were determined using electrospray ionization-ion mobility spectrometry-quadrupole mass spectrometry (ESI-IMS-QMS) while introducing 2-butanol into the buffer gas. The mobilities of the test compounds decreased by varying extents with 2-butanol concentration in the mobility spectrometer. When the concentration of 2-butanol increased from 0.0 to 6.8 mmol m(-3) (2.5×10(2) ppmv), percentage reductions in mobilities were: 13.6% (serine), 12.2% (threonine), 10.4% (methionine), 10.3% (tyrosine), 9.8% (valinol), 9.2% (phenylalanine), 7.8% (tryptophan), 5.6% (2,4-lutidine), 2.2% (DTBP), 1.0% (tetramethylammonium ion, TMA, and tetraethylammonium ion, TEA), 0.0% (tetrapropylammonium ion, TPA), and 0.3% (tetrabutylammonium ion, TBA). These variations in mobility depended on the size and steric hindrance on the charge of the ions, and were due to formation of large ion-2-butanol clusters. This selective variation in mobilities was applied to the resolution of a mixture of compounds with similar reduced mobilities such as serine and valinol, which overlapped in N(2)-only buffer gas in the IMS spectrum. The relative insensitivity of tetraalkylammonium ions and DTBP to the introduction of 2-butanol into the buffer gas was explained by steric hindrance of the four alkyl substituents in tetraalkylammonium ions and the two tert-butyl groups in DTBP, which shielded the positive charge of the ion from the attachment of 2-butanol molecules. Low buffer gas temperatures (100 °C) produced the largest reductions in mobilities by increasing ion-2-butanol interactions and formation of clusters; high temperatures (250 °C) prevented the formation of clusters, and no reduction in ion mobility was obtained with the introduction of 2-butanol into the buffer gas. Low temperatures and high concentrations of 2-butanol produced a series of ion clusters with one to three 2-butanol molecules in compounds without steric hindrance. Clusters of two and three molecules of 2-butanol were also visible. Ligand-saturation on the positive ions with 2-butanol molecules occurred at high concentrations of modifier (6.8 mmol m(-3) at 150°C); when saturated, no further reduction in mobility occurred when 2-butanol was introduced into the buffer gas.
使用电喷雾电离-离子淌度光谱-四极杆质谱（ESI-IMS-QMS），在缓冲气体中引入2-丁醇，测定了一组常见α-氨基酸、四种四烷基铵离子、2,4-二甲基吡啶（2,4-二甲基嘧啶）、2,6-二叔丁基吡啶（DTBP）和缬氨醇的淌度。在淌度光谱仪中，测试化合物的淌度随2-丁醇浓度的增加而有不同程度的降低。当2-丁醇浓度从0.0增加到6.8 mmol m⁻³（2.5×10² ppmv）时，淌度降低的百分比分别为：13.6%（丝氨酸）、12.2%（苏氨酸）、10.4%（甲硫氨酸）、10.3%（酪氨酸）、9.8%（缬氨醇）、9.2%（苯丙氨酸）、7.8%（色氨酸）、5.6%（2,4-二甲基嘧啶）、2.2%（DTBP）、1.0%（四甲基铵离子，TMA，和四乙基铵离子，TEA）、0.0%（四丙基铵离子，TPA）和0.3%（四丁基铵离子，TBA）。这些淌度变化取决于离子电荷的大小和空间位阻，是由于形成了大的离子-2-丁醇簇。这种淌度的选择性变化被应用于分离淌度相近的化合物混合物，如丝氨酸和缬氨醇，它们在仅含N₂的缓冲气体中的淌度光谱中会重叠。四烷基铵离子和DTBP对缓冲气体中引入2-丁醇相对不敏感，这可以用四烷基铵离子中四个烷基取代基和DTBP中两个叔丁基的空间位阻来解释，它们使离子的正电荷免受2-丁醇分子的附着。低缓冲气体温度（100°C）通过增加离子-2-丁醇相互作用和簇的形成，使淌度降低幅度最大；高温（2⁵⁰°C）阻止了簇的形成，在缓冲气体中引入2-丁醇时离子淌度没有降低。低温和高浓度的2-丁醇在没有空间位阻的化合物中产生了一系列含有一到三个2-丁醇分子的离子簇。也可以看到两个和三个2-丁醇分子的簇。在高浓度改性剂（150°C下6.8 mmol m⁻³）时，2-丁醇分子在正离子上达到配体饱和；饱和后，在缓冲气体中引入2-丁醇时淌度不再进一步降低。
