How to Prepare ICP Calibration Standards

Preparing ICP Calibration Standards When Stock Standards Aren’t Available

For routine ICP-MS and ICP-OES analysis, laboratories should use properly documented, commercially prepared standards in the analyte combination, concentrations, and matrix required by the analytical method. This can reduce preparation time, minimize opportunities for calculation or contamination errors, and support consistent calibration. CPI offers both ready-to-order and custom-mixed ICP standards for these workflows.

When a laboratory’s normal standard is not available from on-hand inventory and testing must proceed, an interim calibration standard may need to be prepared from an appropriate stock standard. In those situations, preparation should be based on the applicable analytical method and validated SOP, with attention to working concentration, matrix compatibility, dilution accuracy, contamination control, and QC requirements.

The sections below summarize the key considerations for preparing ICP calibration standards correctly and consistently.

How Do You Prepare ICP Calibration Standards?

ICP calibration standard preparation starts with the analytical method or validated SOP. Select an appropriate stock standard, define the working range, match the matrix, calculate dilutions, prepare cleanly, and verify and document the final standard and required QC.

For routine ICP analysis, laboratories should use properly documented, commercially prepared standards in the analyte combination, concentrations, and matrix required by the method. Interim preparation should follow the laboratory’s validated procedures and quality system.

ICP Calibration Standard Preparation Workflow

Where Should ICP Standard Preparation Start?

Start with the applicable analytical method or validated laboratory SOP, not with the concentration printed on a stock-standard label.

Review the required calibration range, blank composition, stock or intermediate standards, internal standards, ICV/CCV requirements, interference or instrument checks, matrix and acid requirements, source requirements, and acceptance criteria.

How Do You Select an ICP Stock Standard?

Select a stock standard based on the analytes, concentration, matrix, element compatibility, documentation, traceability, validity, storage requirements, and whether a CRM is required by the method or quality system.

How Do You Define the Working Calibration Range?

The working range should support the concentrations expected in samples after preparation or dilution and align with the method, reporting limits, instrument response, and laboratory quality requirements.

• Expected sample concentrations
• Required reporting range
• Detection or quantitation goals
• Sample dilution factors
• Instrument linear dynamic range
• Calibration model and linearity
• QC standard concentrations
• Carryover or memory risk at high levels

Should ICP Standards Be Matrix Matched?

Yes, when required by the method or necessary for analytical performance. Matrix matching is especially important when standards and samples differ in acid concentration, dissolved solids, salts, viscosity, or other components that affect sample introduction and instrument response.

How Do You Calculate an ICP Standard Dilution?

For simple volumetric dilutions, laboratories commonly use C₁V₁ = C₂V₂, where C₁ is stock concentration, V₁ is stock volume, C₂ is target concentration, and V₂ is final volume.

PRACTICAL PREPARATION POINT: A mathematically correct dilution may still be operationally unreliable. When the required transfer volume is too small for accurate routine measurement, use one or more intermediate standards or a custom formulation closer to the working concentration.

Direct Dilution vs. Serial Dilution

How Should an ICP Calibration Blank Be Prepared?

A calibration blank is not simply water. For example, in EPA Methods 200.8 and 200.7, it is reagent water acidified with the same acid matrix as the calibration standards. The blank should follow the applicable method and SOP for reagent-water quality, acid purity and concentration, container cleanliness, and contamination control.

Why Are Calibration Verification and QC Standards Prepared Separately?

Calibration standards establish the calibration curve. Calibration-verification and QC standards check whether calibration and method performance remain acceptable. They should not be treated as interchangeable unless the applicable method or SOP permits it.

How Do You Control Contamination During ICP Standard Preparation?

Trace-metal calibration is vulnerable to low-level contamination, and the lower the calibration range, the more important clean handling becomes.

• Use high-purity acids and diluents
• Use clean labware, tips, caps, and containers appropriate for trace metals
• Control carryover from high-concentration stock standards
• Protect preparation areas from dust, fingerprints, and exposed surfaces
• Avoid metal tools or fixtures that may introduce contamination
• Prevent labeling and transcription errors

What Documentation Should Be Kept for Prepared Working Standards?

Keep enough information for another qualified analyst to reconstruct the preparation.

Common ICP Calibration-Standard Preparation Mistakes

When Can a Custom ICP Standard Reduce Preparation Work?

A custom standard can be useful when a laboratory repeatedly prepares the same multi-element mixture and needs a defined analyte combination, concentration pattern, matrix, and volume.

A custom formulation can reduce repetitive pipetting and transcription steps when technically appropriate and stable, but the requested analytes, concentrations, and matrix still require technical review.