Atomic Spectroscopy

Question 1

What is atomic spectroscopy

Answer 1

We measure what elements are in the sample and how much (thier ratios)

It sensitive (detects things even at very low concentrations like ppm and also sub ppb)

Question 2

Why is the monochromater placed AFTER the sample for atomic spec

Answer 2

The sample is first turned to atoms using a flame atomizer

The flame also emits light so the monochromator needs to be after the sample and the flame

Question 3

What is a line source and why do we use it

Answer 3

The atomic absorption bandwidths are very narrow so to make sure the indecent light bandwidth is less than the absorbance bandwidth we use a lines source

Ex hollow cathode lamp

Question 4

What is a hollow cathode lamp

Answer 4

It has a hollow cathode that’s made of the same metal we are analyzing

This make it so that is generated the same wavelength that the metal absorbs

A voltage to the lamp ionizes the gas in the lamp and the ions hit the cathode and split off the metal from it and hit the glass

Question 5

What are the 3 main ways to do atomization (get sample in instrument and into atoms)

Answer 5

Flame

Furnace

Plasma

Question 6

What is flame atomization

Answer 6

The liquid sample is sent through a nebulizer, the biggest droplets fall out

air carry’s the remaining droplets across the bent path to the flame

The solution gets evaporated then goes into the flame and gets vaporized then decomposed then oxidized then ionized

Wasteful as 5% of sample is lost to the flame

Question 7

What’s the hottest part of the flame

Answer 7

The interconal layer (1200 degrees Celsius)

Question 8

What is the stociometric flame

Answer 8

Best flame for absorption

Has a double cone

No soot or excess O2

Question 9

What is used as the oxidizer for flame atomization

Answer 9

Oxy-acetylene

or NO2

Question 10

What are graphite furnaces

Answer 10

Less precise than flame, but they are more sensitive

The atoms spend more time in the optical path (more of them get measured)

The sample isn’t lost to nebulization (doesn’t get drained)

Solids can be added directly (not just liquids)

Question 11

What are the step to how a graphite furnace works

Answer 11

Drying (drying the sample at 125 degrees for 20s)

Charring (decomposing the sample)

Atomizing (atomized the sample, higher temp better)

Cleaning (cleans out remaining residue)

Question 12

For graphite furnaces, when do you actually measure the analytical signal

Answer 12

The absorbance is measure during the atomizing step

Question 13

What is inductively coupled plasma

Answer 13

Helps with making ionized gas (like Ar and Ar+)

The flame it at a temp close to the temp of the suns surface

Best for emmision because the high temp atomizes and the remaining energy is used for excitation

Question 14

How is the Ar plasma made

Answer 14

The sample goes in through a sample aerosol inlet,

cooling gas inlet inserts cool air flow and keeps the plasma in the middle of the tube and insulates the rest of the torch

The radio frequency load coils (made of hollow cu tubes) send in photons and RF to kick an electron out of Ar to make Ar + + e-

These ions hit other Argon’s and form more ions to eventually make plasma

Question 15

Which atomizer is best for atomic absorbance

Answer 15

We want atoms in the ground stat so a cooler flame or furnace atomizer

Question 16

Which atomizer is best for atomic fluorescence

Answer 16

Want atom to start in ground state

Flame or furnace but flame is best

Question 17

Which atomizer is best for atomic emmision

Answer 17

Either a hot (N2O - acet flame)

Or inductively coupled plasma (BEST)

Question 18

What is the Doppler affect for atomic line widths

Answer 18

The particles travel and emit light but the light compressed near/at the direction the particle is traveling

Question 19

What is pressure broadening for atomic line widths

Answer 19

Increased collisions between gasses decrease the lifetime of the atoms excites state and change/share their velocities

Question 20

What do the Doppler effect and pressure broadening help with

Answer 20

They give measurable line widths for atomic lines

Question 21

What detector do you use for single element analysis in atomic absorption

Answer 21

A photomultiplier tube which helps cause it has a most sensitivity

Question 22

What detector do you use for multi element analysis in atomic emmision

Answer 22

A photodiode array to let simultaneous measurement of many wavelengths

Question 23

What are the types of interferences in in atomic spec

Answer 23

Spectral interference

Chemical

Ionization

Question 24

What is spectral interference

Answer 24

The atoms with overlapping absorbance have their peaks too close together to analyze

Question 25

What is chemical interference

Answer 25

The formation of oxides or refractory (non breaking down) compounds affect the signal

Can use releasing against to stop this

Question 26

What is ionization interference

Answer 26

The formation of ions at a high temp reduces the amount of neutral atoms

Question 27

What is x ray fluorescence

Answer 27

1. Use an X-ray to kick electron out of the core shell of the atom
2. The core is now unstable so the electron for the out shells (K alpha nearest and beta second nearest) go to centre and release a photon as they come in

Works best on heavier elements

Question 28

What is a bremsstrahlung (broad hump)

Answer 28

Point on the x ray fluorescence graph where everything is accessible (all ions aplha and beta)