Mass Spectrometry Flashcards
What is the formula for relative molecular mass?
average mass of molecule / 1/12 mass of one atom of carbon-12
What does the mass spectrometer determine?
The mass of separate atoms
Describe the vacuum in the mass spectrometer
The whole apparatus is kept under a high vacuum to prevent the ions that are produced colliding with molecules from the air
What happens at the beginning of electrospray ionisation?
The sample is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal. This produces tiny positively charged droplets that have lost electrons to the positive terminal. The solvent evaporates from the droplets into the vacuum and the droplets get smaller until they may contain no more than a single positively charged ion.
What happens at the beginning of electron gun?
The sample is vaporised and high energy electrons are fired at it from an electron gun, which is a hot wire filament with a current running through it that emits a beam of high energy electrons which knocks off one electron from each particle forming a 1+ ion.
What happens during acceleration?
Positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed
What happens during ion drift?
Ions pass through a hole in the negatively charged plate, forming a beam and travel along the flight tube to a detector
What happens during detection?
Lighter ions arrive first at the detector as they have higher velocities. The flight times are recorded as the positive ions pick up an electron from the detector which causes a current to flow.
