Magnetic field mapping around two strong mass spectrometers .At AMOLF there are two mass spectrometry instruments which will be moved to University of Maastricht. One of possible locations would be a large room (ca 7x9m) which is adjacent to recently designed and remodeled EM laboratory with highly sensitive TEMs. Since the distance between those mass spectrometers and TEMs is quite limited (approx. 4 m, exact distance depends on the layout of instruments in that room), general concern raised whether there will be negative impact from strong magnets (7 and 9 Tesla) on the working and performance of Ems. By using magnetic field sensor and dynamic signal analyzer, the static magnetic field has been measured in different distances and directions to the main magnet. based on the collected data, the magnetic field lines have been determined as good as possible. Because of limited access to the surrounding area of both mass spectrometry instruments and also the existence of other instruments in direct vicinity, the determined values have to be considered certain accuracy. However for the scope of this survey, the estimated distances within 0.5 meter accuracy should be acceptable. .