Separate matrix-matched calibrations were prepared for each sample type to minimize matrix effects. 150 µL samples of blood or urine were mixed with 150 µL of water and 4.5 mL of assay diluent: 0.5 % (v/v) tetramethylammonium hydroxide (electronics grade, Alpha Aesar, US), 0.005 % (v/v) Triton X-100 (Romil, UK) and 2.5 µg L -1 gallium (Alpha Aesar, US). Blood and urine calibrators comprised 150 µL of each standard with 4.5 mL of assay diluent and 150 µL of either defibrinated horse blood (TSC Biosciences, Buckingham, UK) or deionized water (urine calibrators and blank). Tissue samples up to 150 mg in weight were accurately weighed (Sartorius CP124S analytical balance) and made up to 300 mg with deionized water. Tissue calibrators comprised 150 µL of each calibration standard and either 150 µL defibrinated horse blood (TSC Biosciences, UK) or deionized water (blank). 1 mL of 25% (w/w) aqueous tetramethylammonium hydroxide (electronics grade, Alpha Aesar, US) was added to the tissue samples and calibrators and incubated for 48 hours at room temperature. 1% (v/v) nitric acid containing 5 µg L -1 gallium (Alpha Aesar, US) was added to partially neutralize the sample prior to analysis.