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Ion Yields in UV-MALDI Mass Spectrometry As a Function of Excitation Laser Wavelength and Optical and Physico-Chemical Properties of Classical and Halogen-Substituted MALDI Matrixes

机译:UV-MALDI质谱中的离子收率与激发激光波长以及经典和卤素取代的MALDI基质的光学和理化性质的关系

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The laser wavelength constitutes a key parameter in ultraviolet-matrix-assisted laser desorption ionization-mass spectrometry (UV-MALDI-MS). Optimal analytical results are only achieved at laser wavelengths that correspond to a high optical absorption of the matrix. In the presented work, the wavelength dependence and the contribution of matrix proton affinity to the MALDI process were investigated. A tunable dye laser was used to examine the wavelength range between 280 and 355 nm. The peptide and matrix ion signals recorded as a function of these irradiation parameters are displayed in the form of heat maps, a data representation that furnishes multidimensional data interpretation. Matrixes with a range of proton affinities from 809 to 866 kJ/mol were investigated. Among those selected are the standard matrixes 2,5-dihydroxybenzoic acid (DHB) and alpha-cyano-4-hydroxycinnamic acid (HCCA) as well as five halogen-substituted cinnamic acid derivatives, including the recently introduced 4-chloro-alpha-cyanocinnamic acid (ClCCA) and alpha-cyano-2,4-difluorocinnamic acid (DiFCCA) matrixes. With the exception of DHB, the highest analyte ion signals were obtained toward the red side of the peak optical absorption in the solid state. A stronger decline of the molecular analyte ion signals generated from the matrixes was consistently observed at the low wavelength side of the peak absorption. This effect is mainly the result of increased fragmentation of both analyte and matrix ions. Optimal use of multiply halogenated matrixes requires adjustment of the excitation wavelength to values below that of the standard MALDI lasers emitting at 355 (Nd:YAG) or 337 nm (N_(2) laser). The combined data provide new insights into the UV-MALDI desorption/ ionization processes and indicate ways to improve the analytical sensitivity.
机译:激光波长是紫外矩阵辅助激光解吸电离质谱(UV-MALDI-MS)中的关键参数。仅在对应于基质的高光吸收的激光波长下才能获得最佳分析结果。在提出的工作中,研究了波长依赖性和基质质子亲和力对MALDI过程的贡献。使用可调染料激光器检查280至355 nm之间的波长范围。根据这些辐照参数记录的肽和基质离子信号以热图的形式显示,该数据表示可提供多维数据解释。研究了质子亲和力范围从809到866 kJ / mol的基质。在选择的那些当中,包括标准基质2,5-二羟基苯甲酸(DHB)和α-氰基-4-羟基肉桂酸(HCCA)以及五种卤素取代的肉桂酸衍生物,包括最近推出的4-氯-α-氰基肉桂酸酸(ClCCA)和α-氰基2,4-二氟肉桂酸(DiFCCA)基质。除DHB以外,在固态时,朝着峰值光吸收的红色侧获得了最高的分析物离子信号。在峰吸收的低波长侧始终观察到从基质产生的分子分析物离子信号的减弱程度更大。这种影响主要是由于分析物和基质离子的碎片增加所致。最佳使用多重卤化基质需要将激发波长调整到低于以355(Nd:YAG)或337 nm(N_(2)激光)发射的标准MALDI激光的激发波长。合并的数据为UV-MALDI解吸/电离过程提供了新的见解,并指出了提高分析灵敏度的方法。

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