A new miniaturized microextraction HS-LPME-OIP procedure for ammonium determination based on Nessler's method

A recently proposed combination of headspace liquid-phase microextraction with an optical immersion probe (HS-LPME-OIP) was adapted for the spectrophotometric determination of ammonium. The developed method is based on the conversion of ammonium ions to ammonia in a 0.15 M sodium hydroxide solution, followed by the absorption of ammonia by 200 µL of Nessler's reagent solution preliminary diluted with distilled water (1:16.7). The extracting phase, in which OIP was immersed, was placed into vial fixed in the headspace above the sample solution in a hermetically sealed vessel. The analytical signal was monitored for 30 min at 400 nm. The duration of the analysis can be flexibly adjusted and, if necessary, reduced to 5 min. The level of permissible concentrations of some interfering substances, including calcium, magnesium, iron and some organic compounds, was significantly reduced. The LOD was equal to 0.20 mg L −1 , and the linear calibration range was from 0.70 to 15 mg L −1 . The RSD ranged from 2.5 to 5.2%. The developed method was successfully applied to the analysis of natural waters, fertilizers and CRM samples. Graphical abstract