WHAT IT IS
A collision/reaction cell is a chamber located between the ion source and the mass analyzer in an ICP-MS instrument. It uses specific gases to remove interferences from polyatomic or isobaric ions that may overlap with the analyte's mass-to-charge ratio (m/z). Collision cells employ inert gases, such as helium, for kinetic energy discrimination, while reaction cells use reactive gases, like hydrogen or ammonia, to chemically modify or eliminate interfering ions.
HOW IT WORKS
Ion Introduction – Ions generated in the plasma are directed into the collision/reaction cell, where they encounter a controlled gas environment.
Collision/Reaction Process – In a collision cell, inert gases like helium reduce interferences by colliding with polyatomic ions, dissipating their kinetic energy, and preventing them from reaching the detector. In a reaction cell, reactive gases chemically interact with interfering ions, transforming them into neutral or different charged species that are no longer detected.
Ion Selection – After interference removal, analyte ions pass through the cell and are separated by their m/zm/zm/z ratios in the mass analyzer.
Detection – The purified ion stream reaches the detector, ensuring accurate measurement of the target analytes.
TYPES OF COLLISION/REACTION CELLS
Collision Cells: Utilize inert gases, such as helium, for kinetic energy discrimination. These cells are effective for removing polyatomic interferences while preserving the integrity of the analyte ions.
Reaction Cells: Use reactive gases, such as hydrogen, oxygen, or ammonia, to selectively react with interfering ions. Reaction cells are particularly effective for removing isobaric interferences.
Hybrid Cells: Combine collision and reaction processes, offering flexibility in addressing both polyatomic and isobaric interferences in complex samples.
ADVANTAGES
Effective Interference Removal: The cells eliminate polyatomic and isobaric interferences, ensuring accurate detection of target elements.
Improved Sensitivity: By reducing background noise and interferences, collision/reaction cells enhance the instrument's sensitivity, enabling detection at ultra-trace levels.
Versatility: These cells allow for customized gas selection and flow rates, adapting to various sample matrices and analytical requirements.
Broader Element Range: Interference removal expands the range of measurable elements, including those prone to overlap, such as iron, arsenic, and selenium.
High Precision: Improved interference control supports precise isotopic ratio measurements for advanced applications.
CHALLENGES AND LIMITATIONS
Gas Optimization: Selecting the appropriate gas type and flow rate requires careful optimization to balance interference removal and analyte preservation.
Increased Complexity: The addition of a collision/reaction cell increases the instrument's complexity, requiring skilled operators and additional maintenance.
Gas Costs: The use of specialty gases, such as hydrogen or ammonia, adds operational costs to the analysis.
Throughput Reduction: The additional processing step can slightly increase analysis time, particularly in high-throughput workflows.
Potential Analyte Loss: Overly reactive or poorly optimized gases can react with analyte ions, reducing signal intensity.
APPLICATIONS
Environmental Monitoring
Food Safety
Biomedical Research
Pharmaceutical Analysis
Industrial Applications