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Adaptation of the acetone method for the δ 15 N–NO 3 − analysis of saline water with a low concentration of nitrate
Author(s) -
Tanu Ferdouse Zaman,
Miyata Toru,
Sadzuka Naotaka,
Irie Mami,
Nakanishi Yasuhiro
Publication year - 2020
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8770
Subject(s) - chemistry , acetone , salinity , nitrate , analytical chemistry (journal) , evaporation , solvent , volume (thermodynamics) , reproducibility , chromatography , sample preparation , ecology , physics , organic chemistry , quantum mechanics , biology , thermodynamics
Rationale The recently reported acetone method for δ 15 N–NO 3 − analysis is a straightforward sample preparation process. However, the applicability of the method to water samples having high salinity and low concentration of nitrates is not good. Therefore, we developed a new method to measure δ 15 N–NO 3 − values in a saline sample having low nitrate concentration by improving the acetone method (the adapted method), and verified its usability. Methods The adapted method involves (a) reducing a large volume of sample by evaporation, (b) removing NaCl by mixing acetone twice, (c) changing the volume ratio of the acetone/NaI/ n ‐hexane solvent from 21/0.35/10 to 30/0.25/5 mL, (d) using an increased volume of BaI 2 (0.1 M) – from 0.75 to 1 mL, and (e) using an alternative capsule drying process of lyophilization. Results The adapted method has provided nearly exact δ 15 N–NO 3 − values of standard materials with high precision and accuracy (<0.1‰) at a lower cutoff of 2 μmol of NO 3 − in a sample capsule. The recovery of NO 3 − in this method was significantly dependent ( P < 0.05) on the Cl − concentration of the samples. However, a minimum recovery of 60% NO 3 − , required for the reproducibility of the accurate value of δ 15 N–NO 3 − , was possible from the concentrated sample aliquot containing up to 6 g of Cl − . The application of the adapted acetone method to creek water samples, collected from mangrove watersheds, has shown high consistency in the analysis results. Conclusions It was proved that the inexpensive and easy‐to‐handle adapted acetone method could be used for the δ 15 N–NO 3 − analysis of saline water samples when the sample aliquot contained about 4 μmol of NO 3 − with less than 6 g of Cl − .