Question

in an AES measurement should an external radiation source such as hallow cathode lamp be used? why?

compared to icp emission spectrometry, flame emission spectrometry is little used except for the determinationnof the alkali metals and coccassionally calcium. why?

to measure the Na concentration in an unknown solution by AAS or AES a relatively high concentration of KNO3 or KCl is often added to eash sample. explain.

Answer 1

In AES when an element is introduced into flame, few of its atoms are excited by absorbtion of thermal energy by flame, majority of the electrons remain in the ground state. The excited atom then emits characteristci radiation of the ekement and returns to the ground state. The intensity of the the emited light radiation is directly proportional to the number of excited atoms and hence concentration of element introduced into the flame.

while in AAS element is still introduced into flame but in this case the atoms in the ground state absorb radiation which is characteristic of the element used, further this radiation is same as that is emitted by an excited atoms of the excited element in flame photometry.

further in AES when we are using a hallow cathode lamp, the absorbance of light depends on the no of ground state atoms, while when without it the intensity may depend on flame temperature.

also in AAS it's consistent with Beer- Lambert's law , hence absorbance is linearly proportional to the conc of element under study.

so we should use Hallow cathode lamp

2)

Inductively coupled plasma atomic emission spectroscopy (ICP-AES), is an analytical technique used for the detection of trace metals.

but we still go for the flame FES for group I and Ca²⁺ because of the characteristic colour or the wavelenghth of the light emitted. which confirms it's presence.

3)

we add KCl or KNO3 to the sample, so as to use internal standard method. in which the properties of the internalstandard and the analyte we are studying are similar but itself is not present in the solution.

the process of internal standard is shown below.