Room temperature ionic liquids (ILs) have many applications including as matrices in MALDI. We wished to investigate the efficacy of ILs as matrices in time-of-flight secondary ion mass spectrometry and in mass spectrometric imaging (MS imaging). Two ILs derived from α-cyano-4-hydroxycinnamic acid (CHCA) were synthesized and tested using phospholipids, cholesterol, and peptides. The molecular ion intensities of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), cholesterol, and bradykinin were greatly increased using IL matrices. Further, detection limits were also improved: for DPPC and DPPE detection, limits were at least 2 orders of magnitude better using IL matrices. However, these IL matrices were not effective for the enhancement of angiotensin I ions. The data also indicate that IL matrices are suitable for imaging MS. The IL matrices did not cause changes to the sample surface via matrix crystallization or other processes; no “hot spots” were observed in the mass spectra. As a demonstration, an onionskin membrane was imaged. In the matrix-enhanced MS images, ions characteristic of proteins and other biomolecules were observed which could not otherwise be observed. Clearly ionic liquids deserve further investigation in SIMS and MS imaging.
室温
离子液体(ILs)有许多用途,包括作为 MALDI 的基质。我们希望研究
离子液体作为基质在飞行时间二次离子质谱法和质谱成像(MS iMAging)中的功效。我们合成了两种由 α-
氰基-
4-羟基肉桂酸(CHCA)衍生的 IL,并使用
磷脂、
胆固醇和肽进行了测试。使用 IL 基质大大提高了
1,2-二棕榈酰-sn-
甘油-3-
磷酸胆碱(
DPPC)、
1,2-二棕榈酰-sn-
甘油-3-
磷酸乙醇胺(
DPPE)、
胆固醇和
缓激肽的分子离子强度。此外,检测限也得到了提高:对于
DPPC 和
DPPE 的检测,使用 IL 基质的检测限至少提高了 2 个数量级。不过,这些 IL 基质对
血管紧张素 I 离子的增强效果不佳。数据还表明,IL 基质适用于成像质谱。IL 基质不会通过基质结晶或其他过程导致样品表面发生变化;在质谱中没有观察到 "热点"。作为演示,对洋葱皮膜进行了成像。在基质增强 MS 图像中,可以观察到蛋白质和其他
生物大分子特有的离子,而这些离子在其他情况下是无法观察到的。显然,
离子液体在 SIMS 和 MS 成像中值得进一步研究。