High-precision analyses of potassium isotope compositions using MC-ICP-MS require dealing with the major isobaric interferences related to Ar plasma, ³⁸ArH on ³⁹K and ⁴⁰ArH on ⁴¹K. Several methods were developed to reduce these interferences using cold and dry Ar plasma [1,2] and/or the extra high-resolution mode (XHR) of the Neptune XT (Thermo Scientific) [3]. MC-ICP-MS can be used to obtain high precision analyses of calcium isotopic ratios, with a focus on measuring ⁴²Ca, ⁴³Ca, and ⁴⁴Ca only, ⁴⁰Ca being not measured because of the massive ⁴⁰Ar of the plasma gas. The use of the medium or high-resolution mode is also required to resolve argide isobaric interferences, such as ⁴⁰ArH₂ on ⁴²Ca [4,5]. For both isotopic systems, measurements require high concentrations of analyte (∼1µg/mL), limiting the potential for very low concentrations or small samples. For some years now, MC-ICP-MS equipped with collision/reaction cell (CCR) have provided the advantage of requiring lower concentrations (∼0.1 µg/mL) in low-resolution mode while overcoming interference issues. Using the CCR of the Thermofisher Scientific Proteus [6,7] or the Nu Instrument Sapphire [8-12], some studies have provided high-precision analysis of calcium and potassium isotope ratios. In this work, we will present results of calcium and potassium isotope compositions measurements using the Neoma MC-ICP-MS/MS (Thermofisher Scientific) associated with an APEX Omega desolvator (ESI) and a continuous-flow microFAST Isotope autosampler (ESI). The capabilities of the Neoma’s CCR operating with different configurations will be evaluated and discussed for both elements regarding the remaining interferences, the sensitivity, the influence of acid molarity, the effects of the concentrations mismatch between sample and standard and the matrix effect. The mismatch in analyte concentration between the sample and bracketing standard has been recognized as an important factor that influences the accuracy of the potassium and calcium isotopic ratios particularly with CCR. Here we‘ll present the advantages of the continuous-flow microFAST Isotope autosampler, which allows high-precision and high-throughput analysis over self-aspirating introduction. In comparison with literature studies [6-14] the performances, the benefits and the limitations of different configurations will be discussed.

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