Interference

Interference – An element or substance other than analytes of interest that may cause false highs or lows, false positive, or skewed results. Interference elements may be mistaken by the instrument as the analyte of interest due to similar behavior in instrument, or disrupt the sought after signals, making accurate quantification difficult or impossible.

• There are several types of interference:
  • Spectral – when two elements’ wavelengths or masses are very close and cause overlapping of results.
  • Physical – when differences in the samples cause changes in transport efficiency or its ability to be nebulized (turned into an aerosol mist inside the instrument). This can be from something like complicated or unknown samples, or changes in lab temperature or instrument performance.
  • Chemical – when standards and samples behave differently in plasma due to mismatched matrices.
• Interference Table – Interferences on ICP-OES can be corrected via the use of an interference table. The table is constructed by running high concentrations of very pure single element standards. All method wavelengths are monitored and whenever a response is detected for an element that should not be present in the standard it is noted. For example, running high concentration chromium will produce a signal on specific wavelengths associated with silver. We know that silver is not present in the chromium standard, so this signal is due to an interference. By collecting this data, the instrument software or analyst can use the interference table to help correct their results and provide more accurate results.
• Interference Correction Equations – Interferences on ICP-MS can be corrected via the use of equations built by collecting data on instrument response for known interferents. For example, an ⁵⁰Cr interference on ⁵⁰Ti (this is a spectral interference because both ⁵⁰Cr and ⁵⁰Ti would overlap on each other) may be corrected by monitoring the counts of ⁵²Cr and applying an equation to subtract the ⁵⁰Cr counts from ⁵⁰Ti. See the Inorganic Ventures website or IV Ignite for resources on correcting for interferences!