The Mass Spectromètre Flashcards
How to calculate relative atomic mass
relative atomic mass = average mass of 1 atom
Twelfth of mass of 1 atom of Carbon -12
How to calculate Relative molecular mass
relative molecular mass = average mass of molecule
Twelfth the mass of 1 atom of 12C
What are mass spectrometers used for with chemists
by forensic scientists to help identify substances such as illegal drugs.
What happens in a time of flight mass spectrometer brief
In outline, the substance in the sample are converted to positive ions, accelerated to high speeds , and arrive at a detector.
What order does the mass spectroscopy go in
Vacuum
Ionisation
Acceleration
Ion drift
Detection
data analysis
What happens in the vacuum
The whole apparatus is kept under a high vacuum to prevent the ions that are
produced colliding with molecules from the air.
What happens in electrospray ionisation
sample is dissolved in a volatile solvent
forced through a fine hyperdermic needle that is connected to a positive terminal of a high voltage supply
And particles gain a proton from the solvent as they leave the needle
Forming xH ions
What happens in electron impact ionisation
In electron impact, the sample is vaporised and high energy electrons are fired at it from an electron gun,
which is a hot wire with a current running through it that emits beam of high energy electrons
This usually knocks off one electron from each particle forming a l+ ion.
What happens in acceleration
The 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 In ion drift
The ions pass through a hole in the negatively charged plate, forming a beam and travel along a tube, called the flight tube, to a detector.
What happens in detection
When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector, which causes a current to flow.
What happens in data analysis
The signal from the detector is passed to a computer which generates a mass spectrum
What is high and low resolution mass spectrometry
High resolution measures the relative atomic mass to five decimal places
Low resolution measure the relative atomic mass to one decimal place
What is relative atomic mass
the mass of an atom compared to 1/12 of a carbon-12 atom
What is relative molecular mass
the mass of an molecule compared to 1/12 of a carbon-12 atom