 Alternatively, one can measure cholestane using GC/MS/MS experiments which target the m/z fragment 217 (from molecular ion 372).This specific method first looks for the 372 molecular ion of cholestane, and then fragments that molecular ion further to its m/z 217 fragment in order to improve identification of specific isomers.δ13C values of cholestane reflect the carbon isotope composition of the animals that created the original cholesterol molecules.