Before the 1990s, direct reading spectrometers could only analyze gas elements C and S in metals. Later, with the improvement of spectrometer production technology, gas elements in metals refer to C, S, N, O, and H. Before the 1990s, photoelectric direct reading spectrometers could only analyze C and S.

With the emergence of spectra and photomultiplier tubes that can be used for far ultraviolet, the re-understanding and improvement of inert gas optical systems, photoelectric direct reading spectrometry has made a huge leap in gas element analysis. The analysis of nitrogen is a new breakthrough in photoelectric direct reading spectrometry. Initially, it was measured with a 174.27nm spectral line, but the measurement stability was poor and the nitrogen content was also high, so the actual application was not high. Later, the 149.47nm spectral line was used to determine nitrogen in steel, and the detection limit could reach 5ppm, with good stability.

Previously, carbon was only determined using the 193.09nm spectrum, and the detection limit in steel was 5ppm. Now, the 165.70nm spectrum can be used as needed, and the detection limit of carbon in steel and copper can reach 1ppm. Photoelectric direct reading spectroscopy analysis of oxygen has been carried out in recent years, with a detection limit of 10ppm in copper and 15ppm in steel. Photoelectric direct reading spectroscopy analysis of hydrogen in iron has a detection limit of 8ppm.

Currently, photoelectric direct reading spectroscopy can analyze ultra-low carbon, nitrogen in steel, carbon, sulfur, and oxygen in pure copper, and hydrogen in titanium. Domestic work on determining nitrogen in steel and oxygen in pure copper has also been gradually carried out.

Generally speaking, photomultiplier tubes for determining nitrogen, oxygen, and hydrogen require special optical materials to reduce their own absorption of spectral lines. Therefore, these photomultiplier tubes are much more expensive, so the instrument prices of these channels in the instrument configuration are also more expensive than usual.

In order to ensure the accuracy of direct reading spectrometer in measuring nitrogen, oxygen, hydrogen and other gas elements, high-purity argon must be used. Generally, the purity of argon is required to reach 99.9995% (5N5) or higher. If the purity of argon cannot be guaranteed, it needs to be used with an argon gas purifier.

In general, although direct reading spectrometer has made great progress in analyzing gas elements, it still has a gap in detection compared with dedicated carbon and sulfur analyzers, oxygen and nitrogen analyzers and hydrogen analyzers, and it still has a lot of room for development.