MARK WAINWRIGHT ANALYTICAL CENTRE UNSW
XRF FACILITY
METHODOLOGY:
Oxygen and Nitrogen Analysis:
Approximately 0.0500 grams of powdered sample material is weighed into an oxygen-free tin capsule,
the weight recorded, and the tin capsule placed in a nickel basket. Approximately 0.0500 grams of
graphite is weighed into a graphite crucible. The analysis process is started and the tin capsule loaded
into the assembly head and the graphite crucible loaded upon prompting. If metal pins are provided for
analysis, nickel baskets and graphite in the crucible are not required. Samples weighing from
approximately 0.1000 to 1.0000 grams can be weighed into the tin capsule, provided they fit. The
analysis is performed as described below.
Theory of Operation:
“The TC600 determines both the oxygen and nitrogen content of a sample and uses a self-contained
electrode furnace for fusion. Oxygen is measured by infrared detection as carbon dioxide and carbon
monoxide in an IR cell.
Analysis begins by placing an empty graphite crucible on the lower electrode and pressing the loader
button. The electrodes close and atmosphere is purged from the crucible. High current passes through
the crucible generating heat, which drives off gasses trapped in the graphite. This process is called
outgassing. Next, a sample is dropped from the loading mechanism into the crucible. High current is
again passed through the crucible driving off gasses in the sample. To prevent further outgassing during
analysis, a current lower than outgas current is used. The oxygen released from the sample combines
with the carbon from the crucible to form carbon monoxide and small amounts of carbon dioxide.
High oxygen content sample gasses pass from the furnace to the carbon monoxide and carbon dioxide
detectors. Low oxygen content sample gasses pass through heated rare earth copper oxide which
converts carbon monoxide to carbon dioxide. The sample gasses then pass through the IR cells, which
detect oxygen as carbon dioxide.
Before the sample gasses flow through the measure flow scrubber and TC cell, they pass through the
Dynamic Flow Compensator. As CO2 is trapped by Lecosorb, the sample gas flow rate is reduced. The
dynamic flow compensator adds carrier gas to the sample gasses, maintaining a constant flow rate. In
the presents of high oxygen, this process improves the nitrogen sample results.
After the dynamic flow compensator, sample gasses flow through the measure flow scrubber where
carbon dioxide is removed by Lecosorb to prevent detection by the TC cell. Water vapor is formed when
carbon dioxide is trapped. Since water vapor can be detected by the TC cell, Anhydrone is used to
remove it. Sample gasses then flow through TC cell producing the nitrogen result.” (LECO 2008: 7-3)
Instrumentation:
LECO TC600 Oxygen Nitrogen Analyser
Reference:
LECO, 2008, TC600 Oxygen/Nitrogen Determinator: Instruction Manual. St. Joseph, Michigan: LECO
Corporation.