Trace elements are an essential additive to parenteral nutrition (PN) mixtures. Previous studies have indicated that certain trace elements, in particular copper and iron, may interact with complete PN mixtures leading to precipitate formation. The causes of these incompatibilities have not been fully elucidated. The purpose of this study was to determine factors responsible for common trace element incompatibilities, using X-ray energy dispersive spectroscopy to examine the elemental content of precipitates isolated from stored PN mixtures with added trace elements. Results indicated that copper sulphide precipitated most rapidly in PN mixtures containing Vamin 9 and in mixtures stored in multilayered bags. Copper sulphide precipitation was delayed in PN mixtures containing Vamin 14 and was not observed in PN mixtures stored in EVA bags. Iron phosphate precipitates were observed in Synthamin-containing PN mixtures after storage, but this was prevented in mixtures containing vitamins stored in multilayered bags.