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Highlights • 1 Five kinds of hydrophobic DESs were designed and prepared for the first time. • 2 The prepared DESs showed high extraction efficiency for formaldehyde (HCHO). • 3 The DES was applied to extract and determine of HCHO in biological and gas samples. • 4 Hydrophobic DESs based VA-LLME combined with HPLC method was developed. Abstract Hydrophobic deep eutectic solvents (DESs) are a new class of green solvents, and their research and application are a brand new area. So far, only a few hydrophobic DESs have been reported as extraction solvents. In this paper, five kinds of hydrophobic DESs composed of trioctylmethylammonium chloride and hydroquinone, 4-phenylphenol or 4-cyanophenol are designed and prepared for the first time. Melting point / glass transition temperature and density are also determined for these DESs. Coupled with HPLC, these hydrophobic DESs have been used as extractants in vortex-assisted liquid-liquid microextraction for the selective enrichment and indirect determination of formaldehyde. The optimization of reaction and extraction conditions, such as pH value, reaction time and temperature, concentration of 2,4-dinitrophenylhydrazine, type and dosage of the extraction solvent, speed and time of vortex, salt addition and centrifugation time are investigated in detail. It is found that under the optimized experimental conditions, the calibration curve of this method is linear in the range of 1.0–200.0 μg L−1 with the linear correlation coefficient (r2) of 0.9994. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) are 0.2 μg L−1 and 1.0 μg L−1, and the intra-day and inter-day precision (RSD, n = 5) are 1.1% and 3.5%, respectively. The interference of some common coexisting ions and neutral molecules have been also tested. The proposed method has been successfully used for the determination of formaldehyde from biological and indoor air samples. The recovery of formaldehyde is in the range from 83.1% to 104.4%, and the relative standard deviation is lower than 5.9%. Furthermore, the analytical parameters of the proposed method have been compared with other extraction and microextraction methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel, green and environmental benign TC-AALLME-SFDES technique was developed. • Solid DES was used as extraction solvent. • The method was applied for the determination of TCS and APs from water samples. • The green profile of the method was assessed by analytical Eco-Scale and ComplexGAPI. • The method opened up the application of solid DESs in LLME technique. A novel and green microextraction technique, temperature-controlled air-assisted liquid–liquid microextraction based on the solidification of floating deep eutectic solvents (DESs), was developed and applied for the extraction of triclosan and alkylphenols in different environmental waters. Hydrophobic DESs composed of menthol and myristic acid with melting points slightly higher than room temperature (25 ± 2 °C) were prepared and used as extraction solvent. First, the solid DES was transformed into liquid DES while the aqueous sample was heated in a water bath. Then, fine droplets were formed by withdrawing and injecting the mixture of aqueous sample and DES with a 1 mL pipette several times. After extraction, the solidified DES phase was obtained in an ice water bath. And then the analyses were performed by HPLC-UV. The microextraction parameters were investigated by the Plackett-Burman design and central composite design. The analytical parameters of this method were investigated and good linear ranges (0.5/1.0–400 μg/L, R2 ≥ 0.9950), limits of detection (0.1–0.5 μg/L) and precision (≤5.9 %) were obtained. This method was successfully applied for the determination of triclosan and alkylphenols from five water samples with satisfactory recoveries (80.0–104.3 %). Subsequently, the green profile of the method was assessed by analytical Eco-Scale and Complementary Green Analytical Procedure Index. This method has the advantages of simplicity, rapidity, low cost, high sensitivity and green, which expands the application of solid solvents in liquid–liquid microextraction and has a wide application prospect. [ABSTRACT FROM AUTHOR]

• DESs with low viscosity, density and melting point near room temperature were designed and used. • A centrifugation-free AA-LLME-SFDES method was developed. • Placket-burman design and central composite design were used for the method optimization. • This method was used for simultaneous analysis of bisphenols and PAHs in 15 tea infusions samples. • This method may be developed as a fully automated AA-LLME method. Deep eutectic solvents (DESs) are a new class of green "designer solvent"; its physicochemical properties can be easily tuned by adjusting DES′ constituents, chemical ratio and water content. In this study, three hydrophobic DESs with low viscosity, low density, and melting points close to room temperature were designed and synthesized. Based on these DESs, an air-assisted liquid–liquid microextraction technique was developed based on the solidification of floating DESs for the simultaneous determination of bisphenols and polycyclic aromatic hydrocarbons (PAHs) via HPLC. The microextraction parameters were optimized via the Plackett-Burman design and response surface methodologies. The method shows satisfactory linearity (R2 ≥ 0.9928), a low limit of detection (0.16–0.75 μg L−1) and satisfactory precision (≤2.3%), and was successfully applied for the simultaneous determination of bisphenols and PAHs from tea infusions with satisfactory recoveries (82.0–116.6%). This method is simple, rapid, economical, environmentally compatible, dispersive solvent-frees and centrifugation-free, and has promising applications in food safety. [ABSTRACT FROM AUTHOR]