1.4 - THE MASS SPECTROMETER Flashcards

1
Q

What is the mass spectrometer the most useful instrument for?

A

for the accurate determination of relative atomic masses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Formula for relative atomic mass?

A
average mass of 1 atom
----------------------------------
 1    mass of 1 atom of 12C
---
12
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Formula for relative molecular mass?

A
average mass of molecule
--------------------------------------
 1   mass of 1 atom of 12C
---
12
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does the mass spectrometer determine?

A

mass of separate atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Example of use of mass spectrometers?

A

used by forensic scientists to help identify substances such as illegal drugs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

On what principles do mass spectrometers work?

A

work on the principle of forming ions from the sample and then separating the ions according to the ratio of their charges to their mass

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What type of instrument is a mass spectrometer described to be?

A

time of flight (TOF) instrument

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens in a time of flight mass spectrometer? (3)

A

substance(s) in sample are converted to positive ions

accelerated to high speeds (which depend on their mass to charge ratio)

arrive at detector

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where is the apparatus held under?

A

under a high vacuum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why is the apparatus held under a high vacuum?

A

to prevent ions that are produced colliding with molecules from the air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the two types of ionisation used in this process?

A

electrospray ionisation

electron impact

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens in electrospray ionisation?

A

sample is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does the electrospray ionisation produce?

A

tiny positively charged droplets that have gained a proton from the solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What happens to the solvent? (electrospray ionisation)

A

evaporates from the droplets into the vacuum and the droplets get smaller and smaller until they may contain no more than a single positively charged ion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What happens in electron impact?

A

sample is vaporised and high energy electrons are fired at it from an electron gun

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is an electron gun?

A

hot wire filament with a current running through it that emits beam of high energy electrons

17
Q

What does the electron gun usually do?

A

knocks off one electron from each particle forming a 1+ ion:

X(g) + e^- arrow X^+(g) + 2e^-

18
Q

What is the acceleration process?

A

positive ions are attracted towards a negatively charged plate and accelerate towards it

19
Q

What ions achieve a higher speed?

A

lighter ions and more highly charged ions

20
Q

What is the ion drift?

A

ions pass through a hole in the negatively charged plate, forming a beam and travel along a tube (flight tube), to a detector

21
Q

What happens during detection?

A

ions with the same charge arrive at the detector, lighter ones are first as they have higher velocities. flight times are recorded. positive ions pick up an electron from the detector, which causes a current to flow

22
Q

What happens during data analysis?

A

signal from the detector is passed to a computer which generates a mass spectrum

23
Q

What can the mass spectrometer be used to do?

A

identify the different isotopes that make up an element

24
Q

How are different isotopes detected by the mass spectrometer?

A

it detects individual ions, so different isotopes are detected separately as they have different masses

25
Q

What does the peak height give?

A

the relative abundance of each isotope

26
Q

To what decimal place can mass spectrometers measure relative atomic masses?

A

to five decimal places of an atomic mass unit

27
Q

What is the name of the mass spectrometer that can measure relative atomic masses to five decimal places

A

high resolution mass spectrometry

28
Q

To what decimal point is most work done to?

A

one decimal point

29
Q

What is work done to one decimal place called?

A

low resolution mass spectrometry

30
Q

How may isotopes does chlorine have?

A

two

31
Q

What are the isotopes of chlorine?

A

35Cl and 37Cl

32
Q

What ratio do the isotopes of chlorine occur in?

A

3:1

35Cl 35Cl 35Cl 37Cl

33
Q

What is the percentage of the chlorine isotopes in naturally occurring chlorine gas?

A

75% 35Cl and 25% 37Cl

34
Q

Example of space probe that carries mass spectrometers

A

Mars Rover Curiosity

35
Q

What are the mass spectrometers in space probes used for?

A

used to identify the elements in rock samples

36
Q

What did the mass spectrometer that landed on Titan used for?

A

identify and measure the amounts of the gases in Titan’s atmosphere

after landing it also analysed vaporised samples of the surface