Diamonds are comprised mostly of carbon. Any other elements present in the diamond are normally at incredibly low abundances that are difficult to measure.
For this reason, trace element data for gem-quality diamonds are scarce. Only recently, with improvements in analytical techniques, more diamond suites are being measured for their trace elements.
Why do we want to have trace element data for diamonds? Because this data can help us understand the composition of diamond source fluids better. Gem-quality diamonds do not contain any fluids like fibrous diamonds do, so we need other ways to try get after the fluid composition.
To see the amazing dataset that Mandy Krebs and co-workers produced for gem-quality diamonds from Victor, Newlands and Finsch, check here
Photo of a sulphide-bearing Victor diamond by Sonja Aulbach (Goethe-Universiteit)