Long‐chain ionic liquid based mixed hemimicelles and magnetic dispersed solid‐phase extraction for the extraction of fluorescent whitening agents in paper materials

A novel mixed hemimicelles and magnetic dispersive solid‐phase extraction method based on long‐chain ionic liquids for the extraction of five fluorescent whitening agents was established. The factors influenced on extraction efficiency were investigated. Under the optimal conditions, namely, the pH of sample solution at 8.0, the concentration of long chain ionic liquid at 0.5 mmol/L, the amount of Fe 3 O 4 nanoparticle at 12 mg, extraction time at 10 min, pH 6.0 of methanol as eluent, and the desorption time at 1 min, satisfactory results were obtained. Wide linear ranges (0.02–10 ng/mL) and good linearity were attained (0.9997–0.9999). The intraday and interday RSDs were 2.1–8.3%. Limits of detection were 0.004–0.01 ng/mL, which were decreased by almost an order of magnitude compared to direct detection without extraction. The present method was applied to extract the fluorescent whitening agents in two kinds of paper samples, obtaining satisfactory results. All showed results illustrated that the detection sensitivity was improved and the proposed method was a good choice for the enriching and monitoring of trace fluorescent whitening agents.