Atomic structure: relative masses + mass spctrometer

Question 1

What is the equation for relative atomic mass?

Answer 1

% abundance x mass
of isotope / 100

Question 1

Relative atomic mass?

Answer 1

It is the average mass of an atom of an element on a scale where an atom of carbon 12 is 12.

Question 2

What is relative molecular mass?

Answer 2

The average mass of a molecule on a scale where an atom of carbon 12 is 12

Question 3

What is relative isotopic mass?

Answer 3

mass of an atom of an isotope of an element on the scale where an atom of carbon 12 is 12.

Question 4

What is the mass spectrometer?

Answer 4

Spectrometer gives accurate information about relative isotopic mass and the relative abundance of isotopes.Mass spectrometry can be used to identify elements. Mass spectrometry can determine the molecular mass.

Question 5

Stages of mass spectroscopy?

Answer 5

1. Ionisation
   2.Acceleration
   3.Ion drift
   4.Detection

Question 6

what is ionisation?

Answer 6

ELECTROSPRAY IONISATION: sample dissolved in solvent (eg water or methanol) and injected through a fine hypodermic needle to give an aerosol (aerosol means to give a substance pressure). Needle attached a positive terminal of a high-voltage power supply and particles gain a proton from the solvent as they leave the needle producing positive ion.

ELECTRON IMPACT IONISATION: The high energy electrons come from an ‘electron gun’ which is a hot wire filament with a current running through it that emits electrons. This usually knocks off one electron from each particle forming a 1+ ion.

Question 7

what is acceleration?

Answer 7

The positive ions attracted towards and negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed.

Question 8

What is ion drift?

Answer 8

The ions pass through a hole in the negatively charged plate forming a beam and travels along a tube called a flight tube to a detector.

Question 9

what is detection?

Answer 9

positive ions pick up electrons, current flows - m/z value and time of flight recorded. largest current comes from most abundant ions.

Question 10

when would you use different types of ionisation in a mass spec?

Answer 10

electron impact is used for organic or inorganic molecules with a low formula mass.

electrospray is used for substances with higher molecular mass including biological molecules. e.g proteins.