The multi-collector–inductively coupled plasma–mass spectrometer (MC-ICP-MS) is a hybrid of ICP-MS and TIMS, with the plasma ion source and magnetic sector capabilities of TIMS and high-precision isotope rations available to almost any element on the periodic table. It mitigates isobaric interferences and obviates chemical separation.
The MC-ICP-MS is the abbreviation for a state-of-the-art multiple collector ICP mass spectrometer. It features a double-focusing Nier Johnson design in which the energy spread of the ion beam is compensated to produce a high-quality image. The mass spectrometer comprises an electrostatic analyzer (ESA), followed by a magnetic sector. The various beams, which are separated by mass using the magnet, are focused onto a Faraday detector array. Placed between the magnet and this array are two lens arrays (in the form of a series of plates above and below the ion beam path) that can act as a zoom lens to alter the dispersion of the instrument, removing the necessity for moveable collectors.
As an ion beam passes through a magnetic field, it is deflected. The amount of deflection depends upon the ion energy, the mass of the ion, and ion charge. A conventional sector magnet also focuses the ion beam in the place of the deflection, such that an image of a narrow source slit can be produced in such a simple mass spectrometer without any extra electrostatic lens elements.
This is the basis of single-focusing mass spectrometers, but this simple design provides a buffer from any energy spread present in the beam, which results in a blurred image. This blurring is due to the magnetic deflection being energy- and mass-dependent. It can also be shown that if the pole angle of the magnet is offset from the ion beam path, focusing in the vertical plane can also be achieved. To overcome the blurring due to ion energy spread, a second electrostatic analyzer is combined with the magnet. The deflection from the ESA depends solely on the ion energy (i.e., is mass independent). The radius and position of this ESA can be chosen such that the displacement due to the ion energy spread after passing through the ESA exactly compensates for the displacement produced by the magnet. Such an arrangement is termed “double focusing” and is the approach adopted for all high-resolution magnetic mass spectrometers.
The Nu Plasma HR MC ICP-MS is used to measure trace and ultra-trace quantities of metallic components in various samples from radioactive or nonradioactive sources. Argon plasma (ionized gas) is formed from the collision of argon atoms resulting in argon ions and electrons. The cooling and auxiliary gasses (approximately 15 L/min) are used for the supply of argon. A Tesla coil is used to inject a critical excess of electrons during the time at which radio frequency (RF) energy is being applied through an RF generator. The formed argon plasma is self-sustaining as long as the generator provides sufficient power and the supply of argon is adequate. A liquid sample is introduced into the nebulizer, producing an aerosol. The aerosol is carried to the plasma and is ionized. Some ions are transferred to the lens stack section of the instrument via a series of differentially pumped orifices (sampler and skimmer cones). The ions are passed through the lenses, electrostatic analyzer (ESA), magnet, and zoom lens, and are detected at the collector array.
Sample size is typically <25 ml