Determination of eight artificial sweeteners in wastewater by hydrophilic interaction liquid chromatography-tandem mass spectrometry

Abstract

The development of a method for the simultaneous determination of eight artificial sweeteners, namely aspartame (ASP), alitame (ALI), neotame (NEO), acesulfame (ACS), saccharin (SAC), cyclamate (CYC), sucralose (SCL) and neohesperidin dihydrochalcone (NHDC), under hydrophilic interaction liquid chromatography (HILIC) conditions is presented herein. The ionization of all the compounds was achieved by negative electrospray. Two silica-based columns, a fully porous (XBridge HILIC) and a fused-core one (Kinetex HILIC), were compared. For HILIC optimization, the effect of the following parameters was studied: the mobile phase, column temperature, pH and ionic strength of the ammonium formate buffer. The optimized mobile phase was 5 mM ammonium formate buffer pH 3.5–methanol–acetonitrile (15/10/75 v/v), with a flow rate of 100 μL min⁻¹ at 50 °C. The asymmetry factor of the peaks was lower on the Kinetex HILIC column than that on the XBridge HILIC. The predominant retention mechanism of all the analytes on silica columns seems to be partition to the aqueous layer. The method was validated in tap water and wastewater samples using Kinetex HILIC. Three deuterated internal standards were used, one for each category of sweeteners (dipeptides, sulfamates and sugars). The instrumental limits of detection ranged from 0.24 (SAC) to 4.4 (SCL) μg L⁻¹. The recoveries in influent samples ranged from 39% (CYC) to 97% (NEO), while recoveries were better for the other two matrices. Inter-day precision (%RSD, n = 6) ranged from 4.2% (SAC) to 20% (ALI) in influent samples. The method was applied to influents and effluents from the wastewater treatment plant of Athens for seven consecutive days and high levels of sucralose and sulfamates were found.