Time of flight Flashcards
What is the first step of time of flight
Ionisation
What are the two methods of ionisation
Electron. Impact and electro spray
What happens in electron impact
The vaporised sample has an electron gun fired at it and this consequently knocks off an electron and then the atom will become positively charged
What is the equation for electron impact
X(g) —-> X+ + e-
Describe electro spray
The vaporised sample is forced through a hypodermic syringe and then reacted with a volatile solution at a high voltage connected to the positive terminal. The sample will gain H+ ions and the sample becomes positively charged
Describe acceleration
All ions are accelerated by an electric field and they all have the same kinetic energy. Since al the ions have the same kinetic energy they will disperse based upon their mass (I’m on about the velocity in the mass spectrometer)
Describe ion drift
Ions are attracted to the negative plate and just drift through the time the ions spend in the drift period is based upon their velocity and the larger the ion the slower it moved you can use this to calculate the time of flight
Describe the detection phase
Once the 1+ ions hit the negatively charged plate as they hit the plate they gain an electron this causes the ion to be discharged and then a current to be formed. The abundance of the ion is proportional to the current produced. The detector plate id connected to computer and the mass
define relative atomic mass
the average mass of an atom including its isotopes relative to 1/12 of a carbon 12 atom
define relative molecular mass
the avergae mass of a molecule relative to that of 1/12 of a carbon 12 atom
what charge does the plate in the mass spectrometer have
negative
what is the use of a mass spectrometer
to identify the different ions that make up isotopes
