Development of a simple method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry

A simple method was developed for the determination of nitrite and nitrate in groundwater based on difference of thermal stability of the species in a graphite furnace and detection by high-resolution continuum source molecular absorption spectrometry of NO. •A simple method was developed for the determination of nitrite and nitrate.•The detection was performed by high-resolution continuum source spectrometry of NO.•The method is based on the different acidity/basicity of the two anions.•No pretreatment step of sample is required for the separation of the species.•The method was applied to the analysis of groundwater samples. In this work, it was developed a method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry of NO produced by thermal decomposition of nitrate in a graphite furnace. The NO line at 215.360nm was used for all analytical measurements and the signal obtained by integrated absorbance of three pixels. A volume of 20μL of standard solution or groundwater sample was injected into graphite furnace and 5μL of a 1% (m/v) Ca solution was co-injected as chemical modifier. The pyrolisis and vaporization temperatures established were of 150 and 1300°C, respectively. Under these conditions, it was observed a difference of thermal stability among the two nitrogen species in the presence of hydrochloric acid co-injected. While that the nitrite signal was totally suppressed, nitrate signal remained nearly stable. This way, nitrogen can be quantified only as nitrate. The addition of hydrogen peroxide provided the oxidation of nitrite to nitrate, which allowed the total quantification of the species and nitrite obtained by difference. A volume of 5μL of 0.3% (v/v) hydrochloric acid was co-injected for the elimination of nitrite, whereas that hydrogen peroxide in the concentration of 0.75% (v/v) was added to samples or standards for the oxidation of nitrite to nitrate. Analytical curve was established using standard solution of nitrate. The method described has limits of detection and quantification of 0.10 and 0.33μgmL−1 of nitrogen, respectively. The precision, estimated as relative standard deviation (RSD), was of 7.5 and 3.8% (n=10) for groundwater samples containing nitrate–N concentrations of 1.9 and 15.2μgmL−1, respectively. The proposed method was applied to the analysis of 10 groundwater samples and the results were compared with those obtained by ion chr