The MOCA platform is equipped with a Multicollector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS, Neptune Plus™ High Resolution, ThermoFischer Scientific). Prior to any isotope measurements, samples were prepared in the clean laboratory (class 100, laminar flow) for dissolution and elemental purification.

The MC-ICP-MS is divided in four parts: a sample introduction system, a plasma source, a mass analyzer and a detection unit. While the first two parts (sample introduction system and plasma source) are similar to ICP-MS, the detection unit is specific to MC. The instrument principle is the following: the liquid sample (usually 2% v/v HNO3 matrix) is desolvated (in the introduction system) and then ionized in a hot argon plasma (a volume of partially ionized gas). More precisely, the ion source is inductively coupled argon plasma at 7500K. The argon flow meets an electro-magnetic field induced by a current within the coil. A high voltage ignition spark is applied to the argon gas and electrons are ripped off from argon atoms inducing a chain of collision. Ions are produced, accelerated and focused. More elements are ionized (ionization frequency close to 100%). As a result, the analytes are desolvated, vaporized, atomized and finally ionized. The charged ions are accelerated by pressure differences inside the system (mass analyzer).

In Neptune Plus™ High Resolution Multicollector ICP-MS, the mass analyzer consists of two parts called double-focusing: the electrostatic analyzer (ESA) dispersing ions with respect to ion energy and the magnetic sector dispersing ions with respect to ion energy and mass. The ions are deviated and detected on different collectors (Faraday cups) of the mass spectrometer depending on their kinetic energy and mass (detection unit). The MC arrays allow for detection of multiple ion beams of adjacent isotope masses simultaneously which cancel out beam fluctuations. This improves precision on isotope ratios. When the ion beam enters the cup, the positively charged ions are neutralized by inducing a current through the resistor recorded as a change in voltage. Isotope ratios are calculated by comparing voltages from the different collectors.

This equipment is in a cleanroom.

Applications of this technique:


  • Isotope analysis in various matrices (rock, soil, sediment, selective soil extractions, soil solution, river water, plant tissue): Si isotopes, Mg isotopes, radiogenic Sr isotopes (87Sr/86Sr)
  • Field of applications: thermal waters (anion-rich), polar rivers (low concentration, organic-rich), soil-plant systems


  • Tooth: radiogenic Sr isotopes (87Sr/86Sr)

The platform is open to discuss the analyses you would like to perform.