ThermoScientific Element XR (HR-ICP-MS)
The ThermoScientific Element XR double-focusing sector field-inductively coupled plasma-mass spectrometer (SF-ICP-MS) at the Institute of Mineralogy at the LU Hannover is equipped with a Faraday detector and a dynode combined with a Secondary Electron Multiplier (SEM). Hence it allows detection of a wide range of signal intensities (the dynamic range of counts per seconds encompasses 1012 cps). This enables the analyses of ultra-trace element levels simultaneously with major elements. Three different modes of mass resolution allow separation of molecular interferences from signal peaks of interest, e.g., like 40Ar16O from 56Fe, 40Ar35Cl from 75As, 16O16O from 32S, or 139La16O from 155Gd. Except for H, He, C, N, O, and the noble gases, the Element XR at the Institute of Mineralogy is capable of analyzing every element of the periodic table.
The Element XR offers analyses of solutions via cyclonic or stable introduction system (SIS) quartz glass spray chambers combined with nebulizers made of PFA or glass, and solid samples like glasses, metals, or crystals via connection to the adjacent femtosecond laser ablation system. An ESI SC2 DX autosampler system can be connected to the instrument as well for large numbers of sample solutions to be run overnight. Cones made of Ni (types Jet, H, and X), Pt (type X), and Al (types H, X) are available.
Sources for sample material are aerosols produced by the femtosecond laser ablation system (using He as carrier gas), or dissolved material in an acidified solution (e.g., 3% HNO3). For solution analyses, an internal standard is typically added to the sample solution prior measurement as a reference. These can be elements like e.g., Ge, Rh, In, Re, or Ir, depending on the sample composition.
The sample is ionized in an Ar plasma, the Ion Transfer Optics accelerate the ions and shape and focus the ion beam. The magnet separates the ions depending on their respective mass and focuses them on different trajectories. The Element XR is designed with a reverse Nier-Johnson geometry, i.e. the Electric Sector Analyzer (ESA) is located behind the magnet. The ESA produces an electric field that focuses ions with the same mass but different energy, thus improving abundance sensitivity. Because changes of the ESA field are achieved faster than the magnetic field, mass ranges of up to 30 % of a given mass can be scanned without changing the magnetic field which has a slower response time.
The three resolution modes enable separation of polyatomic mass interferences from the signal of interest. To achieve this, the ion beam passes through one of three different slits, with the smallest slit giving the highest resolution but lowest transmission. Low resolution (R = 300, 5 % peak height) provides the highest signal intensity, but is insufficient to separation e.g. 56Fe peak from 40Ar16O. This is possible with a medium resolution setting (R = 4.000), however, signal intensity drops to ca. 8% compared to low resolution. High resolution (R = 10.000) reduces signal intensity further, but is recommended for isotopes like 75As, 77Se, 78Se, or 155Gd, depending on the matrix. After setting the modes for the respective isotopes in the measurement protocol, they are activated automatically during analysis.