Determination of trace sulfonamides in foodstuffs by HPLC using a novel mixed-mode functionalized ferrocene sorbent for solid-phase extraction cleanup

Abstract

In this paper, a rapid and effective HPLC method, using a new 4-chloro-6-pyrimidinylferrocene-modified silica gel (NFcSi) as a solid-phase extraction (SPE) sorbent, was developed for the purification and determination of trace sulfonamides in foodstuffs. The main influencing factors of SPE including the amount of NFcSi sorbent, sample flow rate, and species and volume of the eluant were investigated and evaluated in a sample pretreatment step. The optimized purification effect was achieved at a sample flow rate of 2 mL min⁻¹ with 100 mg of NFcSi and 5 mL of washing solution (water, 100%). The HPLC analysis was carried out on a Shim-Pack VP-ODS column (150 × 4.6 mm i.d., 5 μm) with a mobile phase of MeOH/0.1% acetic acid–water (30 : 70, v/v). With a detection wavelength of 270 nm, the good linearities of sulfadimidine (SM₂), sulfamethoxazole (SMZ) and sulfadimethoxine (SDM) were obtained at concentrations ranging from 10 to 5000 ng mL⁻¹ (R² ≥ 0.9998). The RSD% values (n = 6) of retention times and peak areas in intra- and inter-day assays for three sulfonamides were all below 0.55%, 1.80%, 0.20% and 0.78%, which showed good precision. In addition, the overall recoveries of SM₂, SMZ and SDM through the extraction and purification steps were in the range of 71.1–86.7%, 70.6–93.6% and 72.4–90.7%. Compared with commercial SPE sorbents, NFcSi featured excellent selectivity to retain polar and nonpolar interferents in sample matrices. The improved method was simple, rapid, accurate and promising for the determination of trace sulfonamides in foodstuffs with complex matrices.