Low-level 40Ca determinations using nitrous oxide with reaction cell inductively coupled plasma–tandem mass spectrometry

Abstract

In inductively coupled plasma mass spectrometry, the most abundant Ca isotope (40Ca) suffers from isobaric interference with argon, hindering the potential for low detection limits of Ca. A powerful approach is to remove the interference by using a reaction gas in a reaction cell. Ammonia (NH3) has proven to be an effective reaction gas by process of a charge transfer reaction. However, NH3 is highly corrosive and toxic and cannot remove isobaric 40 K. Therefore, this work proposes the use of nitrous oxide (N2O) to mass shift the target analyte 40Ca to 40Ca16O+ as a non-corrosive and non-toxic alternative. Instrument performance testing demonstrated that N2O was capable of reaching equivalent detection limits (0.015 ng g−1) and background equivalence concentrations (0.041 ng g−1) to that of NH3 and limited by the blank only. Further investigation of matrix interferences with synthetic standards highlighted that the N2O approach supports the separation of potassium (K) and magnesium (Mg)–based interferences at tested concentrations of more than 600 times and almost 800 times higher than Ca respectively, whereas NH3 was found to only support the removal of Mg. This work highlights a clear advantage of N2O for low-level Ca determinations with high matrix loads, as well as compatibility with other instrumentation sensitive to corrosion that supports reaction cell technology. Graphical abstract

Characterisation of gas cell reactions for 70+ elements using N2O for ICP tandem mass spectrometry measurements

“…No formation of 38 Ar 16 O + was observed on m / z = 54 and, as reported previously, no significant oxide formation was noted for 40 Ar above 0.4 mL min −1 when considering the oxide formation from blank 40 Ca. 25 …”

“…On the other hand, group 2 metals react greatly with N 2 O to form the monoxide product ion, with negligible formation of the dioxide product ion (<0.1%) observed (except Be). As such, the use of N 2 O is a highly effective option of avoiding the isobaric interferences of 40 Ar + and 40 K + on 40 Ca + (as well as 24 Mg 16 O + ) 25,26 and 87 Rb + on 87 Sr + , 26,27 as well as for the removal of isobaric Ba + interferences for measurements of Cs radioisotopes. [28][29][30] Relative sensitivities of the oxide product ion (compared to standard mode) increased down the group, from Mg (13%) to Ba (70%).…”

“…Conversely, mass-shiing the interference allows the target analyte to be analysed at the same m/z as it enters the cellknown as an "onmass" determination. Other gases used for atom transfer reactions include nitrous oxide (N 2 O), [5][6][7][8] carbon dioxide, 9 sulphur hexauoride, 10 and methyl uoride. 11,12 Asymmetric charge transfer reactions remove interferences by transferring the charge of an interference to the reaction gas (e.g.…”

“…Conversely, mass-shifting the interference allows the target analyte to be analysed at the same m / z as it enters the cell – known as an “on-mass” determination. Other gases used for atom transfer reactions include nitrous oxide (N 2 O), 5–8 carbon dioxide, 9 sulphur hexafluoride, 10 and methyl fluoride. 11,12…”

Umweltanalytik: Neue Spurenstoffe in Städten – neue Schadstoffe?

“…Wie jüngste Arbeiten an der Montanuniversität Leoben gezeigt haben, hat Lachgas als Reaktionsgas noch bessere Eigenschaften und senkt aufgrund seiner besonders starken Reaktivität für einige TCEs die Nachweisgrenzen um den Faktor zehn. 14,15) Blätter als Filter…”