Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 4 / 52 / c

The nucleus-count ratios H:${}^6$Li are A, $12:4=3:1$; B, $9:4$; C, $6:4=3:2$; D, $3:2$. Enrichment changes which isotope is counted but not these stoichiometric ratios.

Quantitative lithium integration requires adequate excitation bandwidth, a suitable calibrated pulse, acquisition of the entire broad as well as narrow signal, correct baseline/phasing and no differential saturation. Recycle delays should be long relative to the slowest relevant longitudinal relaxation time, or saturation must be measured and corrected. Exchange and unresolved overlap must be handled in the integrated areas. Proton and lithium spectra also require a stated relative calibration before raw numbers can be compared across nuclei.