Tandem Magnetic Sector [Mass Spectrometry]

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Glossary

WHAT IT IS

Tandem Magnetic Sector Mass Spectrometry, specifically in the form of Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) with a Collision/Reaction Cell, is a highly advanced technique for precise isotope ratio. It combines the high-resolution and multi-isotope detection capabilities of MC-ICP-MS with the interference removal power of a collision or reaction cell.

This new configuration is used in geochemistry, nuclear science, environmental monitoring, and medical research for the accurate measurement of different isotopic systems, especially when isobaric interferences must be corrected without compromising sensitivity or accuracy.

HOW IT WORKS

In MC-ICP-MS, the sample is introduced into an plasma torch, where it is atomized and ionized.The ions are then extracted into the mass spectrometer and pass through a collision/reaction cell before mass analysis.

The collision/reaction cell, located after the interface but before mass separation, is filled with inert or reactive gases (e.g., He, H₂, O₂, NH₃). It selectively removes polyatomic and isobaric interferences through either physical collision (kinetic energy discrimination) or chemical reaction (forming new ions or neutralizing interferents).

The purified ion beam continues into a double-focusing magnetic sector analyzer, which uses both electrostatic and magnetic sectors to achieve high mass resolution and correct for energy dispersion. Multiple Faraday collectors or ion counters detect ions simultaneously, allowing for precise isotope ratio measurement with minimal mass bias.

ADVANTAGES

Ultra-Precise Isotope Ratios: Simultaneous multi-collector detection reduces instrumental noise and drift.

Interference Removal: The collision/reaction cell effectively eliminates argon-, oxide-, and hydroxide-based interferences, particularly useful for challenging isotopic systems (e.g., Fe, Ca, Cr).

High Sensitivity: Efficient plasma ionization and ion optics ensure excellent signal strength, even for low-concentration elements.

Wide Dynamic Range: Capable of analyzing isotopic ratios from major to ultra-trace concentrations within the same sample.

Stable Long-Term Operation: Ideal for high-throughput or long-duration isotope studies, such as time-series analyses and environmental monitoring.

Versatile Sample Compatibility: Applicable to digested rock, metal, biological, and environmental samples.

CHALLENGES AND LIMITATIONS

High Cost and Complexity: Tandem MC-ICP-MS systems are expensive and require specialized facilities, gas handling systems, and trained personnel.

Instrument Tuning and Calibration: Precise tuning of the plasma, ion optics, and collision/reaction cell conditions is necessary to maintain performance.

Matrix Effects: High total dissolved solids or complex matrices can affect ion transmission and measurement accuracy.

Chemical Noise and Side Reactions: Inappropriate gas choice in the reaction cell can produce secondary interferences or reduce analyte signal.

Mass Bias Correction: Despite its precision, MC-ICP-MS still requires internal or external standards to correct for instrument-induced fractionation.