Recommended Column for Phosphate and Phosphite Analysis on Non-Suppressor IC System

Record: 801

Category: Column Selection
Product: I-524A
Sample: phosphoric acid and phosphorous acid

Question
A customer is looking for an anion-exchange column (4.6 × 100 mm, 5 µm) with quaternary ammonium functional groups on a polystyrene–divinylbenzene (S-DVB) polymer base. The detector is refractive index, and the mobile phase is prepared by adding 0.5 mL anhydrous formic acid to 2.5 L of water (pH ≈ 3.5) containing 80 g/L sodium hydroxide. The target analytes are phosphoric acid (H₃PO₄) and phosphorous acid (H₃PO₃). What Shodex column is recommended?

Answer
The Shodex NI-424 (4.6 × 100 mm, 5 µm) can be considered for non-suppressor ion chromatography systems because it is a polymer-based anion-exchange column containing quaternary ammonium functional groups and supports a pH range of 2–11.
However, the proposed mobile phase (with 80 g/L NaOH) would likely exceed the upper pH limit of the column and is not recommended.

For confirmed separation of phosphate and phosphite, the Shodex I-524A (4.6 × 100 mm, 12 µm) is recommended. This column is validated in an official Shodex application using a conductivity detector, as refractive index detection provides insufficient sensitivity for inorganic anions.

Reference application
Anion Standards (3) – I-524A

Summary

• NI-424 may be used for non-suppressor IC, but NaOH concentration must stay within the pH 2–11 range.
• I-524A is recommended for phosphate and phosphite separation (see application).
• Refractive index detection is not ideal; conductivity detection is preferred.
• PEEK housing is compatible with dilute formic acid.

Additional Comments

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