Atomic Spectroscopy

Question 1

General Scheme

Answer 1

Sample vaporisation -> Excitation -> Analysis

Atomization types: continuous/discrete

Question 2

Methods for Sample Atomization (Nebulisation)

Answer 2

High velocity stream of gas breaks up sample into fine droplets (mist)

Question 3

Methods for Sample Atomization (Flame Excitation)

Answer 3

This method has very low efficiency as it excites a low % of analyte.

1. Nebulized sample enters flame
2. Desolution takes place
3. Internal region: solid particles carried to inner core for vaporisation

Question 4

ICP (Definition + Plasma Definition)

Answer 4

Inductively coupled plasmas

(Plasma - conducting gaseous mixture, hot ionised gas with high conc of electrons and ions, most common is Ar, Ar+ + e- being the conductive species)

Question 5

ICP (Advantages)

Answer 5

Very stable, high temperatures achieved, no interference and is low tech

Question 6

AES (Definition)

Answer 6

Atomic Emission Spectrometry

Used for multi-element determinations

Question 7

AES (Scheme)

Answer 7

Sample -> Nebulised -> Plasma -> Wavelength isolation device -> Transducer -> Signal processing -> Computer

Question 8

AES (Applications)

Answer 8

ICP-AES (High stability, low noise, no interference - but expensive): Environmental samples, petroleum, food, geological, biological.

DCP-AES: Metal determination in soil/geological samples

F-AES: Clinical laboratories (K and Na samples)

Question 9

AAS (Definition)

Answer 9

Atomic Absorption Spectrometry

Simple, reliable and cheap

Question 10

AAS (Scheme)

Answer 10

Hollow-Cathode Lamp -> Chopper –> Reference/Burner –> half silvered mirror —-monochromator—> detector

Question 11

AAS (Broadening)

Answer 11

1. Natural - Shorter lifetime = broad line
2. Pressure - High T/High Density = broad line
3. Doppler - Rapid motion of atoms (High T) = broad line

Question 12

AAS (Hollow-Cathode Lamp)

Answer 12

This is a type of [line source] and is element specific. Usually Ne or Ar as gas in the lamp, and is at constant T and p.

Question 13

F(AAS) (Definition)

Answer 13

Flame (AAS) can cover 60-70 elements, good for regular checks however different lamp for each element.

F(AAS) is single/double beam

Question 14

Flame vs ICP

Answer 14

Flame - cheap, simple - BUT low % of analyte excited

ICP - Reliable, low tech, high T, more efficient atomisation, more sensitive - BUT EXPENSIVE

Question 15

AAS vs AES

Answer 15

AAS - Restriced element range but simple + reliable

AES - Flexible for multi-element analysis