Atomic Spectroscopy

Question 1

What is atomic spectroscopy useful for?

Answer 1

is a range of techniques useful for the quantitative and qualitative determination of elements
- used for mainly metallics/metals but can also be used for non-metals

Question 2

What is the difference between atomic absorption spectroscopy and atomic emission spectroscopy?

Answer 2

atomic absorption spectroscopy
- is absorption of energy required to have electrons in the samples outer shell be promoted to a higher level resulting in excitation

atomic emission spectroscopy
- is the emission of energy as the electrons return back to ground state

Question 3

What is the difference between how atomic absorption spectroscopy and atomic emission spectroscopy are seen?

Answer 3

atomic absorption spectroscopy
- does not show colour due to absorption
= would show darker/faded patches at the site/wavelength of absorption

atomic emission spectroscopy
- show colour
= caused by the emission of excess energy as light photons as it returns to grounded state

Question 4

What is inductively coupled plasma optical emission spectroscopy?
ICP-OES

Answer 4

it is an emission technique

- similar to flame emission but uses plasma instead

Question 5

What are the steps involved in ICP-OES?

Answer 5

sample introduction - pumped into the nebuliser via peristaltic pump
nebuliser - converts liquid sample into aerosol
spray chamber - separates the large droplets from the small droplets = smooth sample introduction
ICP source - usually argon
ICP torch - atomises and ionises the sample
radio-frequency generator
optical spectrometer - selects specific wavelengths depending on the elements present
detector

Question 6

What is atomic spectroscopy useful for?

Answer 6

determination of lead in a cosmetic
- analysis of fake cosmetics
analysis of zinc in a mineral formulation
determination of metals in supplements

Question 7

How does the temperature of the plasma affect ICP-OES and atomisation?

Answer 7

would expect ionisation to be a problem as high temperature means that atomisation will occur to a higher extent in ICP-OES compared to flame emission (nearly to completion)

however, the high concentration of electrons in the plasma suppress further ionisation and provide a steady equilibrium between atom and ion

Question 8

What are the advantages of use of plasma sources?

Answer 8

high stability
low noise
low background
better detect limits – the minimum amount of a sample you can analyse

Question 9

What are the two methods of measurement?

Answer 9

simultaneous
sequential

light intensity at a given wavelength is determine using a photomultiplier tube

Question 10

What is sequential measurement?

Answer 10

measures one wavelength at a time

uses moveable optics to focus on each wavelength on the exit slit
- light is usually separated by either Eberts or the Czerny arrangement

Question 11

What is simultaneous measurement?

Answer 11

measures numerous wavelengths at one time

tend to use fixed optics where the parts do not move

• fixed optic, concave grating instrument
• fixed optic, échelle grating instruments