Analytical instruments produce measurements. Reference materials give those measurements context.
For laboratories performing elemental analysis, inorganic standards and reference materials provide known concentrations of elements that can be used to calibrate instruments, verify calibration, monitor analytical performance, and support laboratory quality control.
These materials are used across analytical techniques including:
- ICP-MS
- ICP-OES / ICP-AES
- Atomic absorption spectroscopy (AA/AAS)
- Ion chromatography
- Other elemental and inorganic analytical methods
Depending on the method and quality-control requirements, a laboratory may need single-element standards, multi-element calibration standards, Certified Reference Materials (CRMs), calibration verification standards, interference standards, instrument check standards, or custom formulations.
Selecting the right material therefore requires more than finding the correct analyte on a label. Concentration, matrix, certification, traceability, elemental compatibility, stability, and intended analytical use all matter.
What Is an Inorganic Reference Material?
An inorganic reference material contains one or more inorganic analytes with established property values for use as a reference during analytical measurement.
For elemental analysis, these materials commonly contain known concentrations of metals, metalloids, anions, or other inorganic constituents in a defined matrix.
Examples include:
- A single-element zinc standard
- A multi-element ICP calibration standard
- An ICP-MS tuning solution
- An interference check solution
- An Initial Calibration Verification (ICV) standard
- A Continuing Calibration Verification (CCV) standard
- A custom multi-element standard formulated for a laboratory-specific method
These reference points allow a laboratory to relate instrument response to known concentrations and evaluate whether an analytical system continues to produce acceptable results.
What Is a Certified Reference Material?
A Certified Reference Material (CRM) is a reference material characterized through established procedures and accompanied by documentation that provides certified property values, associated uncertainty, and appropriate traceability.
That distinction is important.
The terms standard, reference material, and certified reference material are sometimes used interchangeably in laboratory conversations, but they do not necessarily describe the same thing.
- An inorganic standard broadly describes a standard containing known inorganic analyte concentrations.
- A reference material (RM) is sufficiently homogeneous and stable with respect to one or more specified properties and has established properties for calibration, method validation, quality control, or another analytical purpose.
- A Certified Reference Material (CRM) is an RM that carries at least one certified property value with associated uncertainty and traceability.
If a method or laboratory quality system specifically requires a CRM, verify that the material being purchased meets that requirement rather than assuming that any analytical standard is equivalent.
CPI offers Peak Performance™ CRMs produced in an ISO 17034-accredited facility and high-quality RMs manufactured and tested in ISO/IEC 17025-accredited laboratories.
What Should You Look for When Selecting a CRM?
When evaluating an inorganic CRM, consider:
- Accreditation and applicable scope
- Metrological traceability
- Characterization procedures
- Measurement uncertainty
- Starting-material purity
- Manufacturing controls
- Stability and homogeneity
- Certificate of Analysis documentation
Documentation is particularly important when reference materials are used in regulated methods or within an accredited laboratory quality system.
How Are Inorganic Standards Used?
The same broad category of inorganic reference materials can serve several different analytical functions.
Instrument Calibration
Calibration standards establish the relationship between analyte concentration and instrument response.
An ICP-MS laboratory, for example, may prepare multiple working calibration solutions from a concentrated inorganic reference standard. Instrument responses obtained from those solutions are then used to establish the calibration curve.
Initial Calibration Verification
An Initial Calibration Verification (ICV) Standard can be analyzed after calibration to independently confirm that the calibration produces acceptable results.
When required by the analytical method or laboratory quality program, the ICV may be produced from a source independent of the standards used to establish the calibration.
Continuing Calibration Verification
A Continuing Calibration Verification (CCV) Standard is analyzed periodically during an analytical sequence to determine whether calibration remains acceptable.
A CCV outside the laboratory's established acceptance criteria can indicate that corrective action is needed before sample results are reported.
Interference Evaluation
Interference Check Standards can help determine whether potentially interfering elements affect accurate measurement of target analytes.
This can be important when spectral, chemical, physical, or matrix-related interferences affect measurement.
Quality Control and Instrument Performance
Inorganic reference materials can also be used to evaluate analytical accuracy, precision, instrument performance, method performance, and other aspects of laboratory QC.
Where Are Inorganic Reference Standards Used?
The applications extend across multiple scientific sectors.
- Environmental laboratories use inorganic standards for metals analysis in water, wastewater, soil, sludge, and other environmental matrices. ICP-OES and ICP-MS are among the analytical techniques used for trace-metal analysis in these laboratories.
- Cannabis laboratories can use inorganic standards for heavy-metals analysis, including ICP-MS workflows.
- Pharmaceutical laboratories use elemental standards in applications such as elemental impurity testing, while food laboratories use them for trace-metals and heavy-metals analysis.
- Petroleum and oil-condition-monitoring laboratories can use inorganic standards for elemental wear-metal analysis.
Different applications may require very different formulations—which is why the intended method should remain central to standard selection.
CPI International Inorganic Reference Materials
CPI International provides Reference Standards, Single Element ICP Standards, ICP Calibration Standards, ICP Quality Control Standards, ICP Tuning and Setup Solutions, and other inorganic reference materials for analytical laboratories.
CPI's Peak Performance™ trace-metal standards are produced using high-purity starting materials with NIST traceability. Available formulations include single-element and multi-element solutions in nitric acid, hydrochloric acid, and specialized mixed-acid matrices.
CPI also supplies custom inorganic standards for laboratories that require specified analytes, concentrations, matrices, volumes, or other formulation requirements.
Frequently Asked Questions
What are inorganic standards used for?
They are used to establish or verify known analyte concentrations during analytical testing. Applications include instrument calibration, calibration verification, method validation, quality control, interference testing, and instrument performance evaluation.
What instruments use inorganic reference materials?
They are commonly used with ICP-MS, ICP-OES, atomic absorption spectroscopy, ion chromatography, and other elemental or inorganic analytical techniques.
What is the difference between an inorganic standard and a CRM?
An inorganic standard is a broad term for a standard containing inorganic analytes. A CRM has certified property values supported by defined metrological procedures, uncertainty information, and traceability.
Are custom inorganic standards available?
Yes. CPI can formulate custom inorganic standards with specified analytes, concentrations, matrices, and volumes for laboratory-specific applications.
Standardize Your Standards
For more than 40 years, CPI International has supported scientists and analytical laboratories with products designed around the realities of laboratory testing. Founded in 1982, CPI has grown from its beginnings manufacturing pre-packed carbon columns for TOX/AOX analysis into a supplier serving analytical laboratories worldwide.
Choosing the right reference material starts with the method, instrument, analytes, concentration, matrix, certification requirements, traceability requirements, stability, and QC purpose.
Explore CPI's full catalog of Reference Standards
Next in the series: Learn how to select calibration materials for your technique in ICP Calibration Standards: Selecting Standards for ICP-MS and ICP-OES.