Long path gas-phase absorption detector using a 235 nm deep-UV LED source for the determination of nitrite, nitrate and total dissolved nitrogen in waters

•A 235 nm deep-UV LED is uesd as the light source for a gas-phase absorption detector.•The maximum S/N ratio is obtained with an 80 cm length detector cell.•Nitrite is converted to gaseous HONO for detection and sub-μM LOD is obtained.•Nitrate is converted to nitrite through photoreduction.•Less/non-hazardous reagents are used for detecting nitrite and nitrate in waters.