Individual stock solutions of compounds were prepared in 5% v/v ACN and 0.1 % v/v FA at a final concentration of 1 mg/mL and stored at -80 • C. Mix stock solutions were prepared in 5% v/v ACN and 0.1% v/v FA at 10 µg/mL and stored at -80 • C. Mix stock was extemporaneously diluted to 500, 250, 125 and 62.5 ng/mL with water.