Mass Spectrometer

Nina hallwood
Flashcards by Nina hallwood, updated more than 1 year ago
Nina hallwood
Created by Nina hallwood over 6 years ago
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As Level Chemistry Flashcards on Mass Spectrometer, created by Nina hallwood on 01/03/2014.
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Question Answer
What does mass spectrometry determine? Relative atomic masses.
Relative atomic masses are measured on a scale on which Carbon 12 is defined as exactly 12. This means the protons and neutrons have relative masses of exactly 1.
Generalise what happens in mass spectrometry. Atoms are converted to ions Accelerated Deflected Detected
What is the instrument kept under so ions do not collide with air molecules? High vacuum.
The sample is investigated in a gaseous state, if the sample is solid what happens to it? It is vaporised first by heating.
Ionisation is the first past of mass spectrometry. What happens at this step? A beam of electrons from an electron gun knock out electrons from atoms or molecules.
Why are electrons knocked off atoms or molecules? To form positive ions.
Positive ions are attracted to negatively charged plates. What step is this? Acceleration, negatively charged plates attract positive ions accelerating them.
There is a slit in the plates, what does this do to the ions? It forms a beam.
Deflection is the next step, what do ions move into? A magnetic field.
The magnetic field deflects the beam of ions into a what? Arc of a circle. (The beam of ions moves into the magnetic field at right angles to its direction of travel)
What does the deflection depend on? HINT m/z Mass to charge ratio. Z is the charge on the ion.
Are heavier ions deflected more of less than lighter ones? Less than lighter ones
What happens in detection? The magnetic field is gradually increased, so ions of increasing mass enter the detector one after another.
Ions strike the detector, lose their charged and create a what? Current, whichever is proportional to the abundance of each ions.
The computer works out the value of the mass to charge ratio by the strength of what? The magnetic field
Four key stages are. Ionisation, acceleration, deflection and detection.
High resolution mass spectrometry is to what decimal place? Five decimal places of an atomic mass.
Most work is done to the nearest whole number, this is called... Low resolution mass spectrometry.
If you had two mass numbers of 20 and 22. With abundances of 90% and 10% how do you work it out? (90x20) + (10x22) /100 =20.2
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