On-line hyphenation of solid-phase extraction to chromatographic separation of sulfonamides with fused-core columns in sequential injection chromatography

• Hyphenated solid phase extraction with on-line chromatography.
• Comparison of five columns for separation of eight sulfonamide antibiotics.
• Comparison of three anion exchange resins for fresh water sample pretreatment.
• Extending of capabilities of the Sequential Injection Chromatography system.
• High performance and cost-saving method for environmental analysis.

On-line sample pretreatment (clean-up and analyte preconcentration) is for the first time coupled to sequential injection chromatography. The approach combines anion-exchange solid-phase extraction and the highly effective pentafluorophenylpropyl (F5) fused-core particle column for separation of eight sulfonamide antibiotics with similar structures (sulfathiazole, sulfanilamide, sulfacetamide, sulfadiazine, sulfamerazine, sulfadimidine, sulfamethoxazole and sulfadimethoxine). The stationary phase was selected after a critical comparison of the performance achieved by three fused-core reversed phase columns (Ascentis® Express RP-Amide, Phenyl-Hexyl, and F5) and two monolithic columns (Chromolith® High Resolution RP-18 and CN). Acetonitrile and acetate buffer pH 5.0 at 0.60 mL min−1 were used as mobile phase to perform the separations before spectrophotometric detection. The first mobile phase was successfully used as eluent from SPE column ensuring transfer of a narrow zone to the chromatographic column. Enrichment factors up to 39.2 were achieved with a 500 µL sample volume. The developed procedure showed analysis time <10.5 min, resolutions >1.83 with peak symmetry ≤1.52, LODs between 4.9 and 27 µg L−1, linear response ranges from 30.0 to 1000.0 µg L−1 (r2>0.996) and RSDs of peak heights <2.9% (n=6) at a 100 µg L−1 level and enabled the screening control of freshwater samples contaminated at the 100 µg L−1 level. The proposed approach expanded the analytical potentiality of SIC and avoided the time-consuming batch sample pretreatment step, thus minimizing risks of sample contamination and analyte losses.