1. Ion-Selective Electrode (ISE) Method

Most modern chemistry analyzers use ISE for sodium.

Reagents include:

• Reference solution / Internal standard

• Electrolyte solution for electrode stability

• Conditioning solution

• Cleaning solution

• Calibration solutions (Low & High Na⁺ standards)

Principle:

The sodium ISE membrane selectively binds Na⁺ ions, generating an electrical potential proportional to sodium concentration. Calibration solutions are crucial for accuracy.

2. Flame Photometry Method

Older or standalone electrolyte analyzers may use flame photometry.

Reagents include:

• Diluent

• Standard sodium solution

• Internal lithium standard (in some systems)

• Cleaning solutions

Principle:

Sodium emits light at a characteristic wavelength (589 nm) when introduced into a flame. The emitted intensity is proportional to concentration.

3. Colorimetric (Photometric) Method

Used in some semi-automatic chemistry analyzers when ISE is not available.

Reagents include:

• Ionophore-based chromogenic reagents

• Buffer solution

• Color-forming indicator dye

• Stabilizers and preservatives

Principle:

Sodium ions react with a specific ionophore dye to produce a measurable color change.

Reagent Format

Sodium reagent kits may include:

• Single bottle (for colorimetric systems)

• Multi-solution packs (ISE systems)

• Standards in sealed ampoules or bottles

• Ready-to-use liquid formulations

Sample Types

• Serum

• Plasma

• Urine (diluted appropriately)

• Whole blood (in ISE blood gas analyzers)