Lycopene, a-carotene and 6-carotene in canned vegetable juice were determined by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) with selected ion monitoring (SIM). The extracted carotenoids were separated on a C-18 reversed phase column with methanol as the mobile phase and cholesterol benzoate as an internal standard (IS). In order to obtain good repeatability, only the peak portion of analytes eluted from the LC column was introduced into the APCI interface by using an auto switching valve. In the positive mode, lycopene, a-carotene and 3-carotene were monitored at m/z 537 and IS was monitored at m/z 369. The limit of detection was 1ng (s/n=4) and the recoveries of lycopene, a-carotene and 3-carotene were 85.1%, 80.0% and 82.8%, respectively. This SIM determination using LC/APCI-MS allows the analyte in samples to be determined without the influence of co-existing substances which cause problems in LC-UV chromatography.
The quantities of the sweetener aspartame (APM) and its decomposed product, diketopiperazine (DKP), in chocolate, soy sauce and miso paste were determined by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry with selected-ion monitoring. APM and DKP were 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 (0.05mol/L, pH4.0) containing 20% methanol as the mobile phase and o-hydroxybenzamide as the internal standard (IS). In the negative mode, APM, DKP and IS were monitored at m/z 293, m/z 261 and m/z 136, respectively. The limit of determination for APM and DKP in the sample was 5g/ g and the recoveries of APM and DKP were 53-83% and 69-101%, respectively. This method enabled the determination, for the first time, of DKP in chocolate, soy sauce and miso paste.
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