To determine working range and linearity, matrix-matched calibrants were used and analysed with triplicate injection (N=13 tested; range: ~1 to 2000 ng L -1 ). TR imprecision was determined with seven consecutive injections of a sample spiked at ~500 ng L -1 . For recovery and repeatability, n=7 replicate matrix-matched mixture standards (~500 ng L -1 ) were analysed after SPE. Background subtraction was also performed using unspiked matrix (n=3) after SPE.