Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms: An interlaboratory comparison of three common measurement approaches
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Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms : An interlaboratory comparison of three common measurement approaches. / Biasi, Christina; Jokinen, Simo; Prommer, Judith; Ambus, Per; Dörsch, Peter; Yu, Longfei; Granger, Steve; Boeckx, Pascal; Van Nieuland, Katja; Brueggemann, Nicolas; Wissel, Holger; Voropaev, Andrey; Zilberman, Tami; Jaentti, Helena; Trubnikova, Tatiana; Welti, Nina; Voigt, Carolina; Gebus-Czupyt, Beata; Czupyt, Zbigniew; Wanek, Wolfgang.
In: Rapid Communications in Mass Spectrometry, Vol. 36, No. 22, 9370, 2022.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms
T2 - An interlaboratory comparison of three common measurement approaches
AU - Biasi, Christina
AU - Jokinen, Simo
AU - Prommer, Judith
AU - Ambus, Per
AU - Dörsch, Peter
AU - Yu, Longfei
AU - Granger, Steve
AU - Boeckx, Pascal
AU - Van Nieuland, Katja
AU - Brueggemann, Nicolas
AU - Wissel, Holger
AU - Voropaev, Andrey
AU - Zilberman, Tami
AU - Jaentti, Helena
AU - Trubnikova, Tatiana
AU - Welti, Nina
AU - Voigt, Carolina
AU - Gebus-Czupyt, Beata
AU - Czupyt, Zbigniew
AU - Wanek, Wolfgang
PY - 2022
Y1 - 2022
N2 - Rationale Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (N-i) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze delta N-15 in NO3- and NH4+ and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. Methods Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure delta N-15 in NO3- and NH4+. The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms N-i to either N2O (CM-N2O) or N-2 (CM-N-2), and (c) the denitrifier (DN) methods. Results The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2O performing superior for both NO3- and NH4+, followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM-N-2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%N-15 of N-i of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to +/- 8.4 parts per thousand for NO3- and +/- 32.9 parts per thousand for NH4+; SDs within laboratories were found to be considerably lower (on average 3.1 parts per thousand). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered. Conclusions The inconsistency among all methods and laboratories raises concern about reported delta N-15 values particularly from environmental samples.
AB - Rationale Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (N-i) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze delta N-15 in NO3- and NH4+ and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. Methods Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure delta N-15 in NO3- and NH4+. The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms N-i to either N2O (CM-N2O) or N-2 (CM-N-2), and (c) the denitrifier (DN) methods. Results The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2O performing superior for both NO3- and NH4+, followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM-N-2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%N-15 of N-i of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to +/- 8.4 parts per thousand for NO3- and +/- 32.9 parts per thousand for NH4+; SDs within laboratories were found to be considerably lower (on average 3.1 parts per thousand). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered. Conclusions The inconsistency among all methods and laboratories raises concern about reported delta N-15 values particularly from environmental samples.
KW - NATURAL-ABUNDANCE
KW - FRESH-WATER
KW - TERRESTRIAL ECOSYSTEMS
KW - DIFFUSION METHOD
KW - SOIL EXTRACTS
KW - AMMONIA DIFFUSION
KW - ORGANIC-MATTER
KW - NITRATE N
KW - N-15
KW - DENITRIFIER
U2 - 10.1002/rcm.9370
DO - 10.1002/rcm.9370
M3 - Journal article
C2 - 35906712
VL - 36
JO - Rapid Communications in Mass Spectrometry
JF - Rapid Communications in Mass Spectrometry
SN - 0951-4198
IS - 22
M1 - 9370
ER -
ID: 321173170