WHAT IT IS
Oxides level is the proportion of analyte ions that form oxide ions in the plasma. It is typically expressed as the ratio of oxide ions to their corresponding parent ions (e.g., CeO/Ce). High oxide levels can lead to isobaric interferences, reducing the accuracy of elemental and isotopic measurements. Managing this parameter is essential for obtaining reliable results, particularly for elements prone to oxide formation, such as rare earth elements and heavy metals.
HOW IT WORKS
Oxide formation occurs in the high-temperature plasma of ICP-MS when oxygen or oxygen-containing species react with analyte ions. Factors influencing oxide levels include:
Plasma Conditions – Lower temperatures or insufficient energy in the plasma can promote oxide formation, as oxygen remains available to react with analytes.
Sample Matrix – High concentrations of oxygen-containing compounds in the sample, such as water or organics, increase the likelihood of oxide formation.
Gas Flow Rates – Imbalances in argon gas flow can alter plasma dynamics, affecting the degree of oxide formation.
Ionization Efficiency – Elements with strong affinity for oxygen or high ionization potentials are more prone to forming oxides.
IMPACT OF OXIDES LEVELS ON PERFORMANCE
Interference: Oxide ions create isobaric interferences by overlapping with the m/z of other analytes, reducing specificity and accuracy.
Reduced Sensitivity: High oxide levels decrease the intensity of parent ions, limiting the instrument’s sensitivity for those elements.
Quantification Errors: Unchecked oxide interferences can distort quantitative measurements, especially at trace levels.
ADVANTAGES OF CONTROLLING OXIDES LEVELS
Improved Accuracy: Minimizing oxides ensures reliable quantification and reduces errors caused by isobaric interferences.
Enhanced Sensitivity: Reducing oxide formation increases the intensity of parent ion signals, improving detection limits.
Broader Elemental Coverage: Controlling oxides allows for the accurate analysis of elements prone to oxide formation, such as rare earth metals.
Reproducibility: Lower oxide levels result in more consistent and reliable measurements across multiple analyses.
STRATEGIES TO REDUCE OXIDES LEVELS
Optimize Plasma Conditions: Increasing plasma energy or temperature helps prevent the formation of oxides by breaking down oxygen-containing species.
Adjust Gas Flow Rates: Fine-tuning argon gas flow improves plasma stability, reducing the likelihood of oxide formation.
Use of Collision/Reaction Cells: These cells can selectively remove oxide interferences, ensuring cleaner ion streams for mass analysis.
Matrix Matching: Matching the sample matrix with standards minimizes the introduction of oxygen-containing compounds that promote oxide formation.
Regular Maintenance: Cleaning and maintaining the plasma torch and sampling interface reduce contamination that could contribute to oxides.