Van Stipdonk Michael J, Ince M P, Perera B A, Martin J A
Department of Chemistry, Wichita State University, Wichita, KS 67260-0051, USA.
Rapid Commun Mass Spectrom. 2002;16(5):355-63. doi: 10.1002/rcm.587.
Electrospray ionization was used to produce distributions of gas-phase cluster ions from solutions of sodium and potassium tetrafluoroborate. The majority of the cluster species followed the trend (MBF(4))(n)M(+), where M=Na and K. The values of n, for both salts, ranged from 1-15. Collision induced dissociation (MS/MS and MS(n)) in an ion trap mass spectrometer was used to determine the dissociation pathways for the cluster ions. The (NaBF(4))(n)Na(+) cluster ions fragmented via two pathways: (a) the loss of one or multiple neutral BF(3) molecules and (b) the loss of one or more NaBF(4) units. Of the two, the product ions corresponding to the loss of BF(3) units were more prominent. Unlike the Na salt, the (KBF(4))(n)K(+) cluster ions decomposed primarily by the loss of one or multiple KBF(4) units. Similar differences in dissociation behavior were observed when the heated transfer capillary, normally used to desolvate ions, was used to investigate cluster ion stability to thermal degradation and dissociation. The dissociation profiles (decrease in ion abundance with increasing activation amplitude) for several (NaF)(n)Na(+) and (KF)(n)K(+) cluster ions were measured and compared to probe the influence of the relative stability of the alkali fluorides (NaF and KF) on the dissociation behavior exhibited by the tetrafluoroborate cluster distributions. We found that the (NaF)(n)Na(+) cluster ions required higher activation amplitudes to induce fragmentation than the corresponding (KF)(n)K(+) species, indicative of stronger ionic bonding and higher gas-phase stability for the former. This in turn indicates that the reaction pathway involving only the loss of one or multiple units of BF(3), favored for the (NaBF(4))(n)Na(+) cluster series, but not for the analogous (KBF(4))(n)K(+) series, may be due to the high gas-phase stability of NaF, and relatively lower stability of KF, towards dissociation.
采用电喷雾电离技术，从四氟硼酸钠和四氟硼酸钾溶液中产生气相簇离子分布。大多数簇物种遵循(MBF₄)ₙM⁺的趋势，其中M = Na和K。两种盐的n值范围为1至15。利用离子阱质谱仪中的碰撞诱导解离(MS/MS和MSⁿ)来确定簇离子的解离途径。(NaBF₄)ₙNa⁺簇离子通过两种途径裂解：(a) 损失一个或多个中性BF₃分子，以及(b) 损失一个或多个NaBF₄单元。在这两种途径中，对应于损失BF₃单元的产物离子更为突出。与钠盐不同，(KBF₄)ₙK⁺簇离子主要通过损失一个或多个KBF₄单元而分解。当使用通常用于使离子去溶剂化的加热传输毛细管来研究簇离子对热降解和解离的稳定性时，观察到了类似的解离行为差异。测量并比较了几种(NaF)ₙNa⁺和(KF)ₙK⁺簇离子的解离谱(离子丰度随激活幅度增加而降低)，以探究碱金属氟化物(NaF和KF)的相对稳定性对四氟硼酸盐簇分布所表现出的解离行为的影响。我们发现，(NaF)ₙNa⁺簇离子比相应的(KF)ₙK⁺物种需要更高的激活幅度来诱导裂解，这表明前者具有更强的离子键和更高的气相稳定性。这反过来表明，仅涉及损失一个或多个BF₃单元的反应途径，对于(NaBF₄)ₙNa⁺簇系列是有利的，但对于类似的(KBF₄)ₙK⁺系列则不然，这可能是由于NaF对解离具有较高的气相稳定性，而KF的稳定性相对较低。
