The NDIR method (non-dispersive infrared spectroscopy) exploits the property of many gas molecules to absorb infrared radiation at characteristic wavelengths. The absorption intensity is directly proportional to gas concentration – allowing individual gas components to be determined selectively and with high accuracy. Typical accuracies are ±1% of full-scale value, with detection limits reaching into the lower ppm range. This makes NDIR the workhorse of industrial gas analysis.

Fresenius Instruments uses NDIR technology in four analyzer series: the GA220 multi-gas analyzer combines NDIR channels with paramagnetic, electrochemical and ZrO₂ sensors for up to 8 simultaneous measurement components. The GA210 is designed as a single-gas analyzer, delivering compact NDIR measurement for one target gas each – such as CO₂, CO or CH₄. The GA150 was developed specifically for solvent vapors: its heated cuvette prevents condensation of low-volatility substances and enables measurement of VOC in industrial exhaust air streams. The GA315 complements the portfolio with specialized formaldehyde measurement.

NDIR-measurable gases include CO₂, CO, CH₄, SO₂, NO, N₂O, H₂O and numerous organic compounds. Not measurable, however, are O₂, N₂, H₂ and noble gases – for these gases, paramagnetic, ZrO₂ or TCD sensors are available. By combining multiple measurement principles in the GA220, Fresenius thus covers virtually all industrially relevant gases in a single device.

The patented automatic zero-point correction without test gas is a central advantage of all Fresenius NDIR analyzers: it ensures long-term stability without regular calibration gas procurement and significantly reduces operating costs – a key difference from competitor systems that depend on expensive reference gases.