GDMS

The sample, in the shape of a pin, is the cathode for a d.c. glow discharge.  Atoms sputtered from the sample surface into the plasma are ionised, and ions exiting the source are analysed by a double focusing mass spectrometer.

Elemental concentrations are determined from the mass separated ion beam currents.  Each isotopic ion beam current is divided by the appropriate isotopic fraction to obtain the part of the total ion beam current due to that element.  Since each element has a different probability for ionisation, each elemental ion current is multiplied by a Relative Sensitivity Factor (RSF) to obtain a uniform basis for comparison.  The elemental ion currents are then summed to obtain the total ion current from the sample (excluding plasma ions).  Each element concentration tabulated is determined by taking the ratio of the corrected element current to the total sample ion current.

RSF values are determined experimentally from the analysis of standards with well characterised contents of the various elements.  As far as possible, RSF values used for a measurement are those determined from standards similar in composition to the samples.  However, RSFs from different matrices appear to be identical within experimental variation and are also independent of elemental concentrations.  If no standard is available or can be devised, an RSF value is estimated from systematics.

Elements can be determined from sub ppm levels to percentage levels.

IGA

Interstitial gases include nitrogen, oxygen, carbon, sulphur, and hydrogen dissolved in a solid material and dispersed through out its matrix. These gases can have significant effects on the physical properties of materials.

Nitrogen, oxygen and hydrogen are measured by inert gas fusion whereby a sample is inserted into a DC electrode furnace, a high current is passed through the sample and the sample fuses releasing the gases which is then detected by infrared or thermal conductivity measurements

Carbon and sulphur are measured by utilising a RF combustion tube furnace. An RF field is applied that results in combustion of the sample releasing the gases, the gases are then measured by infrared detection.

The gases can be determined to sub-ppm levels to percentage levels.