Pre-workout supplements (PWS), like most nutritional supplements, are classified by the Therapeutic Goods Administration (TGA) in Australia as complementary medicines and are therefore subject to much less stringent regulation compared to pharmaceuticals. Complementary medicines (also known as 'traditional' or 'alternative' medicines) include vitamin, mineral, herbal, aromatherapy and homoeopathic products. The overall goal of this thesis was to determine the amounts of stimulants in PWS, both the biogenic amines derived from Citrus aurantium (CA) extracts as well as caffeine and its dimethylxanthine (DMX) derivatives. Research questions have been put forward relating to the components within PWS and whether they comply with any guidelines or regulatory limits and whether differences are evident between PWS made in Australia compared to overseas. To address these questions, the aims were to develop two HPLC protocols for the quantitation of 1) adrenergic amines present in CA-containing PWS and 2) caffeine and DMXs in PWS. These were the first protocols to implement a single quadrupole mass detector (QDa) for rapid mass confirmation in-line with UV-Vis detection on a reverse phase-high performance chromatography (RP-HPLC) system for detection of these compounds.