Boron isotopic pattern

Example Ionic liquids (ILs) are perfect representatives of ionic analytes. LIFDI (essentially FD, cf. Chap. 8.6) spectra of ILs such as IV-hexylpyridinium tetrafluoroborate (Fig. 8.19) are dominated by the cation peak, C here at tn/z 164, that is accompanied by a strong first cluster ion signal, [(C 2+BF4T at m/z 415, and by a weak second cluster ion signal. The corresponding boron isotopic patterns (Bi and B2) are clearly visible. Furthermore, the softness of the FD process is demonstrated by the fact that even the weakly bound cluster ions exhibit almost no fragmentation in metastable ion spectra, but require collisions to induce dissociation [116]. 

Ions corresponding to were observed with an abundance corresponding to the isotopic pattern of boron. 

Fig. 8.19. LIEDI mass spectrum of A -hexylpyridinium tetrafluoroborate in methanol at a concentration of 0.1 pi ml" scanned over the m/z 50-800 range. The insets show the [QA] and [C3A2] cluster ions for comparison of the experimental and calculated isotopic patterns that are characteristic of one and two boron atoms, respectively. Reproduced from Ref. [116] with permission. Elsevier Science Publishers, 2007.

Since the samples contained three isotopic isomers with potential variation in enrichment at each position aU three positions needed to be measured separately for each data point. However because of the nature of the structure of the molecule and the resultant fragmentation patterns, none of the three positions could be measured without interference from one or both of the other two. The use of other derivatives, such as the butyl-boronate or trl- methylsUyl derivatives, did not improve this situation. Thus, corrections for the interfering enrichments needed to be made. Both (70eV) electron Impact Ionization (El) and methane chemical ionization (Cl) were used to take advantage of particular fragments or enhanced signal abundances which occurred in each mode. 

The advances in instrumentation and particularly the arrival of the multicollector inductively coupled plasma mass spectrometers (MC-ICPMS) opened a window for a number of new tracers that were difficult to tackle with the old instrumentation. A pattern for seawater evolution is thus emerging for isotopes of boron and calcium. 

The naturally occurring isotopes of boron,, 0B (19-58%) and UB (80-42%) have spin quantum numbers of 3 and 3/2, respectively. Experimental V(C-UB) values and those calculated using an INDO-MO method, assuming only the Fermi contact mechanism, are given in Table II. (24-27) It is apparent that the calculations account for the major patterns of substituent effects on /(C-B) and that, if the orbital and dipolar mechanisms are important for these coupling constants,... 

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