Determination of five trace anions in electronic-grade hydrofluoric acid by two-dimensional ion-exclusion/ion-exchange chromatography

Abstract

To address the critical technical bottleneck of severe matrix interference in the analysis of trace anions within electronic-grade hydrofluoric acid (HF), a novel online two-dimensional ion-exclusion/ion-exchange chromatography (2D-IC) method was developed. Highly efficient online matrix elimination was achieved by systematically optimizing the first-dimension flow rate and the valve-switching enrichment window. The primary technical breakthrough of this work is the strategic integration of a controlled delay volume that breaks conventional flow path configurations. Specifically, a 3.0 m FEP delay tubing was introduced between the conductivity cell waste outlet (CELL OUT) and the suppressor regeneration liquid inlet (REGEN IN). This configuration targets a previously overlooked interference mechanism: electrolytic fluctuation feedback. The residual ultra-high concentration HF matrix entering the suppressor's regeneration chamber can trigger violent fluctuations in the electrolytic balance, leading to anomalous baseline elevation that severely masks trace chloride (Cl⁻) signals. By rationally leveraging the Taylor–Aris dispersion effect and controlled time delay within the tubing, the sharp matrix pulses are physically smoothed into a steady, low-concentration flow before reaching the regeneration chamber. This strategy completely blocks the suppressor feedback interference, eliminating the matrix masking effect on chloride quantification without compromising analytical sensitivity or altering thermodynamic separation conditions. Method validation demonstrated excellent linearity for five target anions (Cl⁻, Br⁻, NO₃⁻, SO₄²⁻, and PO₄³⁻) within the 0.1–20 µg kg⁻¹ range (r > 0.999), with ultra-low limits of detection (0.005–0.015 µg kg⁻¹). Requiring a single-run time of only 30 min, this highly sensitive and robust method provides a reliable chromatographic strategy for the stringent quality control of ultra-high-purity wet chemicals in the semiconductor and microelectronics industries.