Gas turbines are subject to flue gas limit values which are to be adhered to during operation and regularly checked depending on the size of the system. After commissioning and maintenance work, the system's emission values are checked for adherence to limit values and also the manufacturer's specifications, and documented if necessary. Due to the low NO concentrations, emission measurements during inspection and adjustment work on LowNOx gas turbines need to be extremely accurate. The portable flue gas analyzer testo 350 featuring the combination of NO2 sensor and special NOlow sensor with a resolution of 0.1 ppm enables precisely these requirements to be met. In addition, the integrated gas preparation and special flue gas probe with patented special hose provide protection against NO2 absorption and allow measured values to be compared, irrespective of date and ambient conditions.