Abstract: Extractive electrospray ionization(EESI) mass spectrometry(MS) has been increasingly used for real time trace analysis of various samples with complex matrices. EESI is easy to be implemented in all types of commercially available MS instruments. However, self-assembled simple EESI source is short of long-term stability. An adjustable device specially developed for EESI source was presented in this work. With parameters of ion source spatial location and MS instrument optimized, the detection limit of EESI using the adjustable device to test proline is reduced from 0.5 μg/L to 0.075 μg/L. The representative-amino acids, valine, phenylalanine, proline, histidine, lysine, asparagine, aspartic acid, threonine, tyrosine and glutamine in blood samples obtained from patients with lung cancer have been tested continuously for 5 days and the average RSD for each sample is less than 10%. The experimental results show that the newly developed EESI source has been improved, particularly on the aspects such as stability, precision and sensitivity.