Amino acid profiling by LC-MS

Details of the amino acids measured were published previously.19 (link) Briefly, liquid chromatography-mass spectrometry metabolomic analysis was conducted by using an AB Sciex 4000 QTrap system (AB Sciex, Framingham, Massachusetts, USA). Eight-hour fasting blood was taken and stored as dried blood spot. Each dried sample was dissolved in 100 µL fresh mobile phase solution. The mobile phase was 80% acetonitrile aqueous solution. Amino acid quality control standards were provided by Chromsystems (Grafelfing, Germany). The standards were mixed and dissolved in 2 mL pure methanol and stored at 4°C. Working solution was prepared through 100-fold dilution for metabolite extraction. Analyst V.1.6.0 software (AB Sciex) was used for system control and data collection. ChemoView V.2.0.2 (AB Sciex) was used for data preprocessing.