title: Development of a simple method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry.
abstract: 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 215.360 nm was used for all analytical measurements and the signal obtained by integrated absorbance of three pixels. A volume of 20 μL of standard solution or groundwater sample was injected into graphite furnace and 5 μL 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 5 μL 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 0.33 μg mL(-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 15.2 μg mL(-1), respectively. The proposed method was applied to the analysis of 10 groundwater samples and the results were compared with those obtained by ion chromatography method. In all samples analyzed, the concentration of nitrite-N was always below of the limit of quantification of both the methods. The concentrations of nitrate-N varied from 0.58 to 15.5 μg mL(-1). No significant difference it was observed between the results obtained by both methods for nitrate-N, at the 95% confidence level.
authors: Universidade Federal da Bahia, Instituto de Química, Campus Ondina, Salvador BA 40170-115, Brazil; Instituto Nacional de Ciência e Tecnologia, INCT, de Energia e Ambiente, UFBA, Salvador, BA 40170-115, Brazil. Electronic address: gbrandao@ufba.br.
authors: Geovani C
authors: GC
authors: Brandao
authors: Universidade Federal da Bahia, Instituto de Química, Campus Ondina, Salvador BA 40170-115, Brazil; Instituto Nacional de Ciência e Tecnologia, INCT, de Energia e Ambiente, UFBA, Salvador, BA 40170-115, Brazil.
authors: Geraldo D
authors: GD
authors: Matos
authors: Universidade Federal da Bahia, Instituto de Química, Campus Ondina, Salvador BA 40170-115, Brazil.
authors: Raimundo N
authors: RN
authors: Pereira
authors: Universidade Federal da Bahia, Instituto de Química, Campus Ondina, Salvador BA 40170-115, Brazil; Instituto Nacional de Ciência e Tecnologia, INCT, de Energia e Ambiente, UFBA, Salvador, BA 40170-115, Brazil.
authors: Sergio L C
authors: SL
authors: Ferreira
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000379:methods*; D004784:Environmental Monitoring / Q000379:methods*; D006108:Graphite / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry*; D006851:Hydrochloric Acid / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D009566:Nitrates / Q000032:analysis*; D009573:Nitrites / Q000032:analysis*; D010084:Oxidation-Reduction; D013054:Spectrophotometry, Atomic; D013696:Temperature
chemical_list: D009566:Nitrates; D009573:Nitrites; D006108:Graphite; D006861:Hydrogen Peroxide; D006851:Hydrochloric Acid
keywords: Groundwater; High-resolution source continuum electrothermal molecular absorption spectrometry; Nitric oxide; Nitrite and nitrate determination