The mass spectrometer

The mass spectrometer

• Used for the identification of relative atomic masses. This is useful for identifying substances, such as illegal drugs.
• Mass spectrometers work by forming ions then separating them according to the mass and/or charge (mass-to-charge ratio).

The mass spectrometer: The process

• Step 1: Ionisation
• The sample to be investigated is dissolved in a volatile solvent before being injected through a fine hollow needle that is connected to the positive terminal of a high voltage supply. This forms single positively charged ions.
• Step 2: Acceleration
• The positive ions accelerate towards a negatively charged plate. Lighter ions and ions with higher charges accelerate at a faster rate.

The mass spectrometer: The process

• Step 3: Ion drift
• The ions pass through a hole in the negatively charged plate, forming a beam that travels along the flight tube towards a detector.
• Step 4: Detection
• The flight times are recorded and the ions gain an electron which causes a current to flow.

The mass spectrometer: The process

• Step 5: Data analysis
• The signal from the detector is passed to a computer that produces a mass spectrometer.
• Additional Information:
• Lighter ions and ions with a higher charged arrive first at the detector
• The whole apparatus is kept under a vacuum to prevent the ions from colliding with air molecules