| Title: | Determination of total dissolved nitrogen in seawater by isotope dilution gas chromatography mass spectrometry following digestion with persulfate and derivatization with aqueous triethyloxonium |
| Author(s): | Pagliano E; Campanella B; Shi L; Thibeault MP; Onor M; Crum S; Melanson JE; Mester Z; |
| Address: | "National Research Council of Canada, 1200 Montreal Road, K1A 0R6 Ottawa, Ontario, Canada. Electronic address: enea.pagliano@nrc-cnrc.gc.ca. Consiglio Nazionale delle Ricerche (CNR), Istituto di Chimica dei Composti Organometallici, UOS di Pisa, Via Moruzzi 1, 56124 Pisa, Italy. National Research Council of Canada, 1200 Montreal Road, K1A 0R6 Ottawa, Ontario, Canada. QUASIMEME, NL-6700 EC Wageningen, Bornsesteeg 10, 6721 NG Bennekom, The Netherlands" |
| DOI: | 10.1016/j.chroma.2018.07.055 |
| ISSN/ISBN: | 1873-3778 (Electronic) 0021-9673 (Linking) |
| Abstract: | "In this study, we propose a novel approach for the determination of total dissolved nitrogen (TDN) in seawater combining high-precision isotope dilution GC-MS with persulfate digestion. A 2?ª+mL sample aliquot was digested with an alkaline solution of persulfate to convert nitrogen containing compounds to nitrate. Digested samples were spiked with (15)NO(3)(-) internal standard and treated with aqueous triethyloxonium to convert the analyte into volatile EtONO(2). This derivative was readily separated from the matrix under gaseous form and could be sampled from the headspace before GC-MS analysis. The resulting chromatograms showed a stable flat baseline with EtONO(2) as the only eluting peak (retention time 2.75?ª+min on a DB 5.625 column). Such an approach provides specificity and obviates the shortcomings of current detection methods employed to analyze seawater samples after digestion with persulfate. In negative chemical ionization mode, the method reached a detection limit of 0.5?ª+mumol/kg TDN (7?ª+ng/g N) and could be applied to quantify seawater samples with 1-25?ª+mumol/kg TDN. On the upper end of the range, quantitation could be repeated within 1%, whereas on a 6?ª+mumol/kg TDN sample repeatability was 2.3% on eight measurements. The method was employed in two proficiency testing exercises providing results in agreement with consensus values. We investigated the impact of reagent blank and we implemented a blank-matching optimal design to account for such contribution. Finally, we performed a study on the yield of persulfate oxidation for organic and inorganic nitrogen compounds typically present in seawater. Whilst nitrite and ammonium are fully converted to nitrate, more complex organic molecules showed recoveries varying from 70% to 100%" |
| Keywords: | Amino Acids/analysis Calibration Gas Chromatography-Mass Spectrometry/*methods Indicator Dilution Techniques Limit of Detection Nitrates/analysis Nitrites/analysis Nitrogen/*analysis Onium Compounds/*chemistry Peptides/analysis Reference Standards Seawate; |
| Notes: | "MedlinePagliano, Enea Campanella, Beatrice Shi, Lisa Thibeault, Marie-Pier Onor, Massimo Crum, Steven Melanson, Jeremy E Mester, Zoltan eng Netherlands 2018/08/05 J Chromatogr A. 2018 Sep 28; 1569:193-199. doi: 10.1016/j.chroma.2018.07.055. Epub 2018 Jul 18" |
