Define the ion before choosing the standard
Select an ion chromatography standard by considering ion identity, concentration, solvent or matrix and method together. The catalogue’s anions include chloride, bromide, fluoride, nitrate, phosphate and sulfate; cations include ammonium, sodium, potassium, calcium and magnesium. Sharing a stock concentration does not make these products interchangeable.
Anion and cation separations may require different analytical conditions. EPA Method 300.0, for example, concerns inorganic anions and should not automatically be applied to cation standards.
What does 1000 mg/L describe?
A label stating 1000 mg/L Cl⁻ does not mean 1000 mg of sodium chloride per litre. Confirm whether the value is expressed as the target ion, an element or another chemical basis. Likewise, nitrate expressed as nitrate and phosphate expressed as phosphate cannot be directly equated with values expressed as nitrogen or phosphorus.
Document the path from stock to working standard
Assess stock suitability alongside calibration levels, dilution equipment and matrix requirements. If preparing a new multi-ion mixture, check component compatibility, stability and method suitability rather than assuming any single-ion standards can be combined.
- Record the stock product code, lot, expiry and dilution date.
- Distinguish calibration standards from standards used for quality-control checks.
- Transfer uncertainty or traceability statements only within the relevant certificate’s scope.
Four questions before ordering
- Which ion and concentration basis are required?
- Does the method measure anions or cations, and which matrix is specified?
- Do stock concentration and pack size match planned consumption?
- Are lot documentation, storage and post-opening instructions available?
Sources
Primary and institutional sources consulted in preparing this article.
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