Total flash evaporation of NaLiBO₂⁺ for high sensitivity analysis of lithium by thermal ionisation mass spectrometry (TIMS)

Precise isotopic measurement of lithium is of utmost importance in the field of geo-chemistry, astrophysics, nuclear industry and bio-medicine. Thermal Ionisation Mass Spectrometry is considered to be the most suitable technique for the isotopic measurement of various elements because, it offers best possible precision due to the low energy spread among the ions generated in the ion-source and high selectivity for the elements of interest. The major source of bias in isotopic measurement in TIMS, is from ion source isotope fractionation which causes continuous preferential evaporation of the lighter isotope resulting in changing isotope ratio with time. The lighter the element or evaporating species higher the fractionation effects, which results in poor measurement precision for elements like lithium especially when atomic ions are used. An alternate gateway to solving this problem is, exhausting the loaded sample by continuous heating of the filament and collection of all the ions formed in the source at the detector end in what is termed as Total evaporation and ion integration. Attempts have been made in this laboratory to measure the lithium isotopic composition using atomic ions by this technique and it was found that, though the isotopic measurement is very sensitive and requires only a few nanograms of lithium, the accuracy of the measured ratio is largely affected by the amount of the sample loaded on the filament. So to have a reasonably good precision in the measurement using atomic ions, stringent analytical conditions and a high level of operator skills is required