Determination of Sulfonamides in Milk by Cloud Point-Salting Out Extraction and Ultra-High-Performance Liquid Chromatography Tandem Mass Spectrometry

Innovative approaches in cloud-point extraction

Cloud-point extraction (CPE) is a pre-treatment technique for the extraction and preconcentration of different chemical compounds, such as metal ions, pesticides, drugs, phenols, vitamins etc., from various samples. CPE is based on the phenomenon of two phases (micellar and aqueous) forming after the heating of an aqueous isotropic solution of a non-ionic or zwitterionic surfactant above the cloud-point temperature. If analytes are added to the surfactant solution under suitable conditions, they should be extracted into the micellar phase, also called the surfactant-rich phase. Recently, the traditional CPE procedure is being increasingly replaced by improved CPE procedures. In this study, recent advances in CPE over the last three years (2020 - 2022), including the application of various innovative approaches, are reviewed. In addition to the basic principle of CPE, alternative extraction media in CPE, CPE supported by various auxiliary energies, a different modified CPE procedure and the use nanomaterials and solid-phase extraction in combination with CPE are presented and discussed. Finally, some future trends for improved CPE are presented.

Preconcentration of sulphonamides in bovine milk by the cloud point extraction method using smartphone-based digital images

Sulphonamides are a group of synthetic antibiotics used specially in veterinary medicine. Among the procedures employed in the sample preparation for sulphonamide determination are liquid-liquid extraction (LLE) and solid-phase extraction (SPE) that use large volumes of organic solvents. Hence, a clean procedure was developed based on preconcentration and cloud point extraction (CPE) without using organic solvents to quantify total sulphonamides in bovine milk. The procedure was optimized as follows: 2 mL of pre-cleaned milk sample, 2 mL of reagent solution and 1 mL of Triton X-114 7% (m/v) were added to a tube, heated in a water bath at 40 °C for 10 minutes and centrifuged at 2950 rcf for 20 minutes. Digital image acquisition was employed directly at the tube without removing the supernatant/aqueous phase. The linear response was observed between 10 and 400 μg L^-1 of total sulphonamides and described by the following equation: S = 2.50 + 0.0514C (μg L^-1) and R = 0.999. The LOD and the CV (n = 11) were estimated to be 10 μg L^-1 and 1.3%, respectively. The main interferents present at their usual concentrations in the sample did not interfere with the results. Spike and recovery tests of total sulphonamides were carried out in UHT and pasteurized milk with recovery values between 73 and 106% and the results obtained for this kind of sample were in agreement with those achieved by a high performance liquid chromatography (HPLC) procedure at the 95% confidence level. The analytical procedure presents an adequate sensitivity to determine total sulphonamides in bovine milk and does not require organic solvents, being aligned to the principles of green chemistry.

Stable Isotope Labeling by Carbon-13 in Bacteria Culture for the Analysis of Residual Avermectin Using Stable Isotope Dilution Liquid Chromatography Tandem Mass Spectrometry

This study describes the development of a new stable isotope labeling method by carbon-13 in bacteria culture (SILCB) for the analysis of residual antibiotics via liquid chromatography with tandem mass spectrometry (LC-MS/MS). Stable isotope dilution (SID) LC-MS/MS with QuEChERS was employed to determine avermectin, particularly avermectin B1a (AV-a) and B1b (AV-b), based on completely ¹³C-labeled internal standards (¹³C-ISs) obtained from the SILCB. Our SILCB was developed from an optimal inorganic medium using ¹³C₆-glucose for Streptomyces avermitilis (14893 strain). A rough extract containing ¹³C-ISs was purified via high-speed countercurrent chromatography with a volatile two-phase solvent system composed of n-hexane/ethyl acetate/methanol/0.5% formic acid in water (7/3/5/5/, V/V). The purified ¹³C-ISs were evaluated to confirm the presence of completely ¹³C-labeled ions with m/z 938 > 326 and m/z 923 > 309 for AV-a and AV-b, respectively. The QuEChERS approach with the ¹³C-ISs procedure achieved acceptable recovery rates in beef meat samples of 99.5 - 100.0% (RSD < 2.0%, n = 6). For the analysis of residual antibiotics in foodstuffs by SID-LC-MS/MS and QuEChERS, the SILCB represents a significant improvement over previous methods suffering from cumbersome sample preparation and matrix effects.