研究目的
To optimize an existing spectrophotometric method based on the Griess reaction for determining nitrate concentrations in hypersaline water samples, addressing the lack of specific methods for such high-salinity conditions.
研究成果
The optimized Griess assay using VCl3 as reductant, with specific conditions (60°C, 40 min, 17.5 mM VCl3, 70 mM Na-citrate, no EDTA), provides a reliable, simple, and cost-effective method for NO3? determination in hypersaline waters, with good recovery rates and a linear range of 0.55-50 μM. This is the first protocol specifically designed for such samples, enhancing environmental monitoring capabilities.
研究不足
The method has moderate precision (4.3-15.4% CV) and is limited to NO3? concentrations up to 50 μM. It may be affected by chemical interferences in high-salinity matrices, and further reduction of NO3? to NO at high temperatures or VCl3 concentrations could occur. No certified reference material for hypersaline waters was available.
1：Experimental Design and Method Selection:
A Box-Behnken design (BBD) was used for multivariate optimization of five factors (incubation temperature, reaction time, EDTA concentration, Na-citrate concentration, VCl3 concentration) affecting the Griess assay, with absorbance at 543 nm as the response. Surface response methodology (SRM) was employed to find optimal conditions.
2：Sample Selection and Data Sources:
Synthetic hypersaline water with Na-Mg-Cl-SO4 composition was prepared to match the salinity of Pétrola Lake (TDS ≈ 78.5 g/L). Natural water samples were collected from Pétrola Lake, Spain.
3：5 g/L). Natural water samples were collected from Pétrola Lake, Spain.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Reagents included VCl3, EDTA, trisodium citrate, sulfanilamide, N-naphthyl ethylenediamine dihydrochloride, HCl, and ultrapure water. Equipment included a multi-mode plate reader (Cytation 5, BioTek), ion chromatograph (Metrohm 930 Compact IC Flex), automated titrator (Metrohm 855 Robotic Titrosampler), and Eppendorf tubes.
4：Experimental Procedures and Operational Workflow:
For each sample, 500 μL was mixed with EDTA, Na-citrate, Griess reagent (sulfanilamide and NEDD solutions), and VCl3 in specific concentrations. After incubation, absorbance was measured at 543 nm. Calibration curves were prepared with NO3? standards in hypersaline water.
5：Data Analysis Methods:
Data were analyzed using Minitab 18 software for BBD and ANOVA. Precision was calculated as coefficient of variation (CV%), limit of detection (LOD) as 3.3 times residual standard deviation divided by slope, and recovery rates from spiked samples.
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