Discrimination of illegal cooking oil is a conundrum in the fields of analytical chemistry and food safety due to complicated sample systems, lack of common targets, and stringent demand of ultrahigh detection sensitivity for corresponding analytical methods. Capsaicin, one of the exogenous molecules that is subsistent in recycled kitchen waste oils, can be regarded as a target for illegal cooking oil identification. Nowadays, tracing capsaicin in oils is implemented mainly by high-performance liquid chromatography–mass spectrometry, which displays shortcomings in high costs and incapableness for field test. Here, we established a surface-enhanced resonance Raman scattering approach to detect capsaicin and identify illegal cooking oils by means of the molecular derivatization treatment of capsaicin. This method features high detection sensitivity with the detection limit of 1.0 × 10^–8 M, rapid response (<7 min detection duration), and simplicity in sample pretreatment, which is available for fast field test of illegal cooking oils.

Surface enhanced Raman scattering (SERS) is an ultra-sensitive spectroscopy technique, which can provide rich structural information for a great number of molecules, while solid phase micro-extraction (SPME) is an efficient method for sample pretreatment in analytical chemistry, particularly in a micro-system. In the present report, a silver-loaded and graphene-based magnetic composite (Fe₃O₄@GO@Ag) was fabricated for use as both a SERS-active substrate and SPME material. The π–π stacking and fluorescence quenching abilities of GO make the composite a perfect candidate for SERS in analyzing real-world samples. Therefore, through combining the magnetic nanoparticles with a SPME device, we have developed a pretreatment method named as disperse magnetic solid phase micro-extraction (Dis-MSPME). In comparison to traditional SPME, the proposed Dis-MSPME realized solid phase micro-extraction from a dispersive system and largely improved the extraction efficiency. Furthermore, by combining the advantages of both Dis-MSPME and SERS we have proposed a new detection method called Dis-MSPME-SERS. Finally, as an example, the illegal additive chloramphenicol (CAP) was successfully detected in aqueous solution with low LOQ and LOD values (1.0 × 10⁻⁸ and 1.0 × 10⁻¹⁰ M, respectively), which was finalized within 10 min based on the proposed Dis-MSPME-SERS method. Therefore, a simpler, more efficient and sensitive approach to realize enrichment, magnetic separation and detection, all-in-one, for the detection of illegal additives has been reported, which will be promising towards the detection of trace amounts of substance in micro-systems.

A bimetallic organic gel (MOG-Fe/Al) was synthesized through the solvothermal method. The gel state of the product obtained under optimized gel formation conditions is sufficient to carry 2 g of weight for a long time. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Brunauer–Emmett–Teller (BET) technique, and X-ray photoelectron spectroscopy (XPS) analysis confirmed the structures and morphologies of the synthesized materials. MOG-Fe/Al, with good stability, excellent durability, and wide applicability, exhibited efficient MO adsorption capacity as high as 335.88 mg/g at 25 °C. Adsorption-influencing factors including solution pH, contact time, and temperature were investigated. The adsorption performance of the bimetallic organic gel was better than that of the monometallic organic gels (MOG-Fe and MOG-Al), and its adsorption processes were in accordance with the pseudo-second-order kinetic and Langmuir isothermal models. The excellent adsorption capacity of the MOG-Fe/Al is due to its surface structure, pore volume, π-π interactions, hydrogen bonds, and electrostatic interactions.

Azo-coupling reaction-based SERRS indirect approach for SAL detection, with a LOD of 1.0 × 10 ⁻¹¹ M within 7 min for real samples.