The apparatus for analyzing a sample gas includes a source of microwave energy directed onto the sample gas to create a plasma. A spectrometer is arranged to receive light from the plasma to identify different elements and/or to determine the concentration of at least one element in the sample gas. In one embodiment, an attached calibration system is provided for calibrating the output of the spectrometer. The calibration system includes a nebulizer apparatus for introducing a controlled amount of at least one element into the sample gas. The apparatus also includes structure adapted to add a swirl component to the plasma gas flow as an aid to plasma confinement. It is also preferred that a pair of electrodes contacting the sample gas be provided for igniting the plasma.