Mass Spectroscopy

Mass analysis was performed on the Waters 2695 (Milford, Massachusetts, USA) Quadrupole Mass system, at electron-spray ionization mode, positive ionization, capillary voltage 3.5 V, cone voltage 60 V, extractor voltage 3 V, RF lens voltage 1V, source temperature (80°C) desolation temperature (150 °C), desolation gas flow( 350 L h^-1) and cone gas flow (50 L h^-1).

Mass spectra were obtained from mixture of methyldopa with dextrose and lactose blended in 1:1 mass ratio then mixture with 20 %(v/w) water and stored in the 90 °C for 5 days. Each sample powder was dissolved in a mixture of methanol: water solvent (50:50) to the approximate concentration of 100 µg mL^-1and injected to mass detector. Mass resolution was calculated by dividing the peak intensity into peak width at the half of the maximum peak height.