Ultra-Trace Determination of Sudan I, II, III, and IV in Wastewater by Solid-Phase Microextraction (SPME) and on-Line Solid-Phase Extraction (SPE) with High-Performance Liquid Chromatography (HPLC)

Two extraction/preconcentration methods are reported for the high-performance liquid chromatography (HPLC) determination of Sudan I, II, III, and IV in wastewater at trace (μg/L) and ultra-trace (ng/L) levels for the first time. The first approach, based on solid-phase microextraction (SPME), allows sub-μg/L determination of Sudan I and II, while Sudan III and IV are not detectable at these levels due to strong binding to dissolved organic matter. For Sudan I and II, the linearity was tested in the range from 0.5 to 50 μg/L and limits of detection (based on a signal-to-noise ratio of 3) and quantification (based on a signal-to-noise ratio of 10) of 0.2 and 0.5 μg/L, respectively, were estimated for both dyes. The on-line solid-phase extraction (SPE) using a C18 based enrichment precolumn was employed in the second approach. The only sample pretreatment employed was a required centrifugation step to remove suspended solids. In this case, the linearity was verified in the range from 50 to 500 ng/L for Sudan I, II, and III and from 100 to 500 ng/L for Sudan IV. The detection limits for a sample volume of 20 mL were on the order of 20 ng/L for Sudan I, 25 ng/L for Sudan II and III, and 30 ng/L for Sudan IV.