Selection, purpose, addition, monitoring, and troubleshooting
for ICP-MS elemental analysis.
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An ICP-MS internal standard is an element or isotope added at a consistent concentration to measured solutions. Its response is used to monitor and correct changes in analyte signal caused by instrument drift, sample-introduction variation, and matrix effects.
The internal standard should not be a target analyte or a meaningful native component of the sample, and it should behave similarly to the analytes it is used to correct.
Internal standards help compensate for changes in instrument response that could otherwise bias measured analyte concentrations.
|
Issue |
Can Help? |
Key Point |
|
Instrument drift |
Yes |
Useful when the internal standard experiences similar drift to the analyte. |
|
Sample transport differences |
Often |
Can help compensate for nebulization and transport variation. |
|
Matrix suppression / enhancement |
Often |
Correction depends on the internal standard behaving similarly to the analyte. |
|
Polyatomic or isobaric interference |
No / limited |
Requires interference-specific correction or other controls. |
|
Incorrect standard preparation |
No |
Internal standardization cannot repair an incorrectly prepared calibration standard. |
|
Contamination |
No |
Use blanks, clean preparation, reagent control, and appropriate laboratory practices. |
Select an internal standard that behaves as much like the analyte as practical while remaining distinguishable from the analyte and absent from the sample at meaningful levels.
→ Method fit: Confirm the element is allowed or appropriate for the analytical method and instrument configuration.
→ Sample absence: Avoid elements that are naturally present at levels that materially change the added internal-standard signal.
→ Mass / ionization behavior: Favor an internal standard with sufficiently similar mass and/or ionization behavior to track analyte response changes.
→ Interference risk: Confirm the selected isotope is free from significant spectral or polyatomic interference and does not create interference on target analytes.
→ Matrix compatibility: The internal standard must remain soluble, stable, and chemically compatible with the calibration and sample matrix.
→ Signal quality: Choose a concentration that produces a stable, measurable signal without creating detector, contamination, or interference problems.
Common internal-standard elements include scandium, yttrium, rhodium, indium, terbium, holmium, lutetium, bismuth, lithium-6, gallium, and germanium, depending on the method and instrument.
No single element is ideal for every analyte or matrix. Multi-element ICP-MS methods often use several internal standards distributed across the mass range so each analyte can be corrected using a suitable reference element.
Internal standards can be added directly to each blank, calibration standard, QC material, and sample, or introduced online through a separate pump channel and mixed with the sample stream before nebulization.
→ Direct addition: Requires consistent volumetric addition and sufficient mixing to ensure homogeneity.
→ Online addition: Can improve consistency during routine sequences, but tubing dimensions, uptake rate, mixing volume, and stabilization time become important.
Whichever approach is used, the internal standard should be added consistently to all relevant measured solutions, and the solution matrix should be compatible with standards and samples.
There is no universal internal-standard concentration for every ICP-MS method. The concentration should provide adequate precision while avoiding contamination, detector issues, or interference problems.
For online addition, the stock solution may need to be more concentrated than the effective concentration reaching the nebulizer because the internal-standard pump channel may deliver a smaller flow than the sample channel.
ICP-MS software monitors the internal-standard response during analysis and compares it with the response observed during calibration. If the internal-standard signal changes, the software applies a correction to associated analytes according to the method and instrument settings.
The correction assumes that the analyte and assigned internal standard are affected similarly. That assumption is why internal-standard selection matters.
1. Start with the method — Confirm any required internal-standard list or assignment rules.
2. Group analytes — Consider approximate mass range and analytical behavior.
3. Review interferences — Check spectral, polyatomic, and sample-matrix interference risks for each candidate.
4. Check sample presence — Avoid candidates naturally present in the sample at meaningful levels.
5. Verify signal quality — Confirm the internal-standard signal is stable and sufficiently intense.
6. Validate performance — Use QC recovery, drift checks, matrix spikes, and representative samples.
7. Document assignments — Record the selected internal standard for each analyte in the method or instrument settings.
A sudden or progressive change in internal-standard response can be diagnostic information indicating a change in the measurement system.
A custom internal standard solution can be useful when a laboratory routinely runs the same ICP-MS method and needs a specific combination of internal-standard elements, concentration, matrix, and volume.
→ Repeated workflows: The same internal-standard mixture is used across routine analytical sequences.
→ Fewer preparation steps: A prepared mixture can reduce repetitive manual additions and dilution steps.
→ Matrix requirements: The required matrix differs from a catalog formulation.
→ Inventory planning: Routine volume needs are predictable.
Custom formulations should still be evaluated for compatibility, stability, and method suitability. The formulation should be based on analytical requirements, not convenience alone.
→ Analytical method or application
→ Target analytes
→ Required internal-standard elements
→ Desired concentration of each internal standard
→ Final matrix and acid concentration
→ Direct or online addition
→ Required volume and packaging
→ Regulatory or quality-system requirements
→ Instrument platform and sample matrix, when relevant
CPI International supports laboratories performing ICP-MS and other elemental analysis workflows with:
For laboratories repeatedly preparing the same internal-standard mixture, CPI custom inorganic standards allow the laboratory to specify analytes, concentrations, matrix, volume, and other formulation requirements.
No. Internal-standard choice depends on the method, analytes, mass range, sample matrix, instrument configuration, and interference profile.
Yes, when internal standardization is used, they should be added consistently to the relevant calibration standards, blanks, QC materials, and samples according to the analytical method and laboratory procedure.
Generally no. The internal standard should not be a target analyte or be present in the sample at a level that materially changes the added internal-standard signal.
No. A tuning solution evaluates instrument setup and performance. An internal standard solution is used during analysis to monitor and correct response changes.
Use the complete technical guide for deeper detail on internal-standard selection, addition, concentration, analyte assignment, response monitoring, troubleshooting, and custom formulation considerations.