Instant Notes: Analytical Chemistry

of individual elements present may be identified. This is the technique of ICP-

E14 Mass spectrometry

Quantitative measurements are possible with both ICP-AES and ICP-MS.

Argon gas is supplied at 10-15 l min-^1 through the three concentric quartz tubes

of the torch, shown in Figure 1(a). The tangential flow of gas in the outer tube

contains the plasma, while the central tube carries the nebulized sample

droplets suspended in argon.

The plasma is established by high-voltage ignition and sustained by the

magnetic field of the radiofrequency generator providing 2 kW of power at

about 27 MHz. The sample is pumped into the nebulizer and the finest droplets

carried forward by the gas, while other, larger drops flow to waste from the

spray chamber. Viscous solvent systems should be avoided. High-solids nebu-

lizers, where particulate matter and slurries are introduced into the ICP, have

been developed. Laser ablation, where the sample is vaporized by a laser

Inductively
coupled plasmas

210 Section E – Spectrometric techniques

Fireball

Sapphire jet

Plume

Tunnel

RF coil

Concentric

quartz tubes

Auxiliary argon

Leakage argon

Sample aerosol

in argon

Transfer

optics

Radio

frequency

generator

Argon Nebulizer

Pump

Sample To waste Computer

Spray

chamber

Microprocessor

and

electronics

Spectrometer

ICP PMT

torch

(a)

(b)

Fig. 1. (a) The ICP torch. (b) Schematic of an ICP-AES spectrometer.