18 19 Isotope dilution mass spectrometry

Question 1

Describe the isotope dilution principle

Answer 1

addition of isotopically-enriched substance to the analysed sample
Mixing of isotopic standard and the sample effectively “dilutes” the isotopic enrichment of the standard and this forms the basis of isotope dilution

Question 2

How is IDM similar to internal standard method?

Answer 2

standard (isotopically-enriched substance) is directly added onto the sample

Question 3

What are the advantages and disadvantages of spiking the sample with RI?

Answer 3

cheap cuz can get from nuclear reactors
no background correction cuz RI not present in sample
detected with extreme sensitivity

Disadvantages:
RI decay
health hazards

Question 4

What are the advantages and disadvantages of spiking with stable isotopes?

Answer 4

Advantage:
dont decay
no health hazards

Disadvantage:
expensive cuz spike is prepared by ‘filtering’ out the target isotope from NE
high natural background cuz sample and spike consistt of exactly the same SI

Question 5

Define isopologue and isotopomer

Answer 5

pologue: same chemical structure but different isotopic composition
pomer: same chemical structure and same number of each nuclide at different positions

Question 6

What is this referring to? same chemical structure but different isotopic composition

Answer 6

isopologue

Question 7

What is this referring to? same chemical structure and same number of each nuclide but at different positions

Answer 7

isotopomer

Question 8

What type of elements are ICP-MS and TIMS used for in inorganic IDMS?

Answer 8

quantifying heavy elements

Question 9

Inorganic MS is used for quantitative analysis. T or F

Answer 9

True

Question 10

What does TIMS stand for?

Answer 10

Thermal Ionization Mass Spectrometry

Question 11

Which MS is used to quantify light elements?

Answer 11

isotope ratio mass spectrometry

Question 12

Describe thermal ion source

Answer 12

measure isotope ratio
process whereby atoms are desorbed from the hot surface and in the process, spontaneously ionized

based on electron transfer between neutral atom and a hot metal

Question 13

What are the advantages of thermal ion source?

Answer 13

high accuracy and precision
clean spectrum obtained
sample in solid form on metal filaments are in highly pure form

Question 14

Describe inductively coupled plasma

Answer 14

ICP converts atoms in the sample to ions
Argon gas flows in channels found in the ICP torch
power is supplied to the load coil, oscillating electric and magnetic field are formed at the torch
when a spark is applied to the argon flowing through the torch,they become ions
these ions are caught in the electric and magnetic fields and then collide with other argon atoms, thereby generating plasma

Question 15

What are the advantages of ICP?

Answer 15

high ionization efficiency

multi-element capability

Question 16

Describe faraday’s cup and what are the advantages of faraday’s cup

Answer 16

Ions enter the cup and since they are moving charged particles, a current can be produced

Robust

Lim: accuracy/precision affected by signal drift

Question 17

Describe SEM/ channeltrons

Give advantages and disadvantages

Answer 17

When an ion enters the channeltrons and hits the wall,electron can be ejected. When this electron hits the walls further, cascade of electrons

Advantages: high sensitivity

Disadvantage: accuracy limited by counting statistics, dead time and cup efficiency

Question 18

Describe multi-collector arrays and give advantages and limitations

Answer 18

Multiple detectors side by side
When ions enter the magnetic sector, it gets split up into individual ion beams
Detectors can them move accurately to where the ions are coming out from.
This shows that MC can do a continuous measument of ions at the same time

Advantages: precision, isotope ratio unaffected by drift in ion current
Limitation.

Question 19

What is specific activity?

Answer 19

number of decays per second