Professor Went: Atomic Emission Spectroscopy

Question 1

What is Spark-Source Emission Spectroscopy used for?

Answer 1

It is a well established technique, useful for determining inorganic constituents in solids; particularly metals.

• Used in scrap-metal yards and metal-casting facilities.
• Can be mobile, self-contained, CCD instruments with programmed calibrations of common metals.
• Operator touches the metal surface with sparkgun.
• Allows for rapid analysis before casting.
• Can sort metals according to type in scrap centres.

Question 2

What is the process of Spark-Source Emission Spectroscopy?

Answer 2

• High voltage arc or spark is struck across the electrode gap.
• Sample is vaporised, forming an atomic vapour of elements (some of which are excited).
• Excited levels have short half-lives and drop back to the ground state, emitting photons. The emitted light passes into a dispersive element and a number of lines are obtained.
• Quantitative analyses need care as intensity depends on time of exposure, concentration of elements etc.

Question 3

What are characteristics of Flame-Source Emission Spectroscopy?

Answer 3

• Similar to spark except the source of excitation is a flame.
• Emission spectrum is much simpler and as a solution of the sample is introduced into the flame, it is easier to quantify.
• Intensity of emission is directly proportional to the concentration of analyte in the aspirated solution.
• A calibration curve is needed as there are many possible interferences.

Question 4

What are the different sources of interference in Flame-Source Emission Spectroscopy?

Answer 4

• Spectral line interference: Analyst is dependent on the quality of the monochromator for selectivity and resolving lines.
• Band interference: Emission lines are often superimposed on bands emitted by oxides and other molecular species from the sample, fuel or oxidant. This is corrected by recording intensity of the background either side of the peak.

Question 5

What is Plasma Emission Spectroscopy?

Answer 5

• A type of atomic emission spectroscopy
• The source is an Inductively Coupled Plasma Torch.

Question 6

What does an ICP torch consist of?

Answer 6

• Consists of three concentric quartz tubes through which streams of Argon flow.
• At the top is a water-cooled induction coil powered by RF generator.
• Flowing argon is ionised by a spark. Resulting ions interact with fluctuating magnetic field produced by induction coil.
• This causes the ions and electrons within coil to flow in closed angular paths
• Resistance of movement causes heat. Sample is aspirated into the tube by flow of argon gas.

Question 7

What are some advantages of Plasma Emission Spectroscopy?

Answer 7

• More complete atomisation of sample
• Background emission is low in observation region.
• Ionisation can be high, but ion lines can be used in preference to the atom lines.
• Oxide formation is nil.
• Low level of self-absorption due to high proportion of excited atoms. Response is linear over many orders of magnitude.
• Good detection limit, low chemical interference and reproducible.

Question 8

What are some disadvantages of Plasma Emission Spectroscopy?

Answer 8

• Spectral interferences
• Expensive operating costs
• Requires solution samples.