Determination of aspartame and diketopiperazine in food by liquid chromatography atmospheric pressure chemical ionization mass spectrometry

The quantities of the sweetener aspartame (APM) and its decomposed product, diketopiperazine (DKP) in chocolate, soy sauce and mise paste were determi ned by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry with selected-ion monitoring. BPM and DKP wer e extracted from the foodstuffs with water and a solid-phase extraction was carried out. The extracted APM and DKP were separated on an analytical C-4 reversed-phase column with ammonium formate buffer (0.05 mol/L, pH 4.0) co ntaining 20% methanol as the mobile phase and o-hydroxybenzamide as the int ernal standard (IS). In the negative mode, APM, DKP and IS were monitored a t m/z 293, m/z 261 and m/z 136, respectively. The limit of determination fo r APM and DKP in the sample was 5 mu g/ g and the recoveries of APM and DKP were 53-83% and 69-101%, respectively. This method enabled the determinati on, for the first time, of DKP in chocolate, soy sauce and miso paste.