What is the difference between nitrogen mode and nitroso/nitro mode?

The 800 Series TEA operates in two main modes. The mode you use depends on which compounds you need to detect.

Nitroso/nitro mode

This is the mode used for nitrosamine and nitro compound analysis. The GC effluent enters a pyrolyser operating between 250 and 700°C. Under vacuum, nitroso compounds cleave at the N-NO bond and nitro compounds cleave at the NO₂ bond, releasing nitric oxide radicals. These react with ozone in the reaction chamber, producing light that is detected by a photomultiplier.

A CTR (catalytic trap removal) cartridge can be used to remove pyrolysis by-products before the reaction chamber, producing a cleaner signal.

This mode is selective for compounds containing nitroso or nitro groups. Other nitrogen-containing compounds that do not contain these groups do not produce a signal. This is what makes the 800 Series TEA so effective for nitrosamine analysis in complex matrices: it ignores everything that is not a nitroso or nitro compound.

Nitrogen mode

Nitrogen mode uses a catalytic pyrolyser operating at 700 to 850°C. At this temperature, all nitrogen in any nitrogen-containing compound (except molecular N₂) is converted to nitric oxide. The detection step is the same: the NO reacts with ozone and the resulting light is measured.

This mode responds to all nitrogen-containing compounds, not just nitroso and nitro species. It is used when the analytical question is about total nitrogen content rather than specific compound classes.

Nitrogen mode with catalyst is available on the 820 Series.

Which should you use?

If you are testing for nitrosamine or explosive residues, use nitroso/nitro mode. If you need to measure total nitrogen across all compound types, use nitrogen mode.

Get in touch if you need help choosing the right mode for your application.