This sophisticated instrument (I mean ICP-AES) allows multi-elemental analysis and is fast revolutionizing the conventional flame emission method of seawater analysis in terms of trace metals. Basically an ICP source consists of a flowing stream of argon gas ionized by an applied radio frequency field typically oscillating at 27.1 MHz. This field is inductively coupled to the ionized gas by a water-cooled coil surrounding a quartz “torch” that supports and confines the plasma. In this case, the sample is introduced into plasma via an ultrasonic or pneumatic nebulizer chamber system similar to that used in the conventional AAS. In the plasma, the sample is subjected to temperatures of about 7000 to 10,0000K, and electrons of the atoms of elements contained in the sample undergo a transition to excited state by absorbing thermal energy from the plasma source that are then re-emitted at a characteristic frequency (atomic spectra) as they return to lower energy state. Thus the elements present may be determined by resolving individual spectral lines of the element of interest and choosing and measuring the intensity of one or more of the carefully selected lines for each element.

Regarding the other instrument nasty DJ knows well

Thanks Sir (Dr. Mitra) for your cooperation with this question. 

ICP-OES and ICP-AES are used interchangeably, represent the same thing.

Thanks Dr. Mitra for giving a very impressive explanation