Mixed working solution was prepared by mixing CYA and MEL
stock solutions at a concentration of 0.5 mg L1 in 10% (v/v)
methanoic acid inwater solution. The 13C3-melamine stock solution
had a concentration of 40.0 mg L1 in methanol. The 15N3-cyanuric
acid stock solutionwas at a concentration of 40.0 mg L1 in 1% (v/v)
methanoic acid inwater solution. Mixed internal standard working
solution was made by combining internal standard stock solutions
at a concentration of 1.0 mg L1 in 1% (v/v) methanoic acid inwater
solution. Stock solutions were sonicated for 30 min at 30 C.