Biodiesel consists of various fatty acid methyl esters (FAMEs) that are mainly produced through transesterification of plant oil or animal fat. It is essential for biodiesel to be purified utmostly to meet its product standard before being traded, while the universal purification method has been water washing. However, water washing inevitably causes the residual of FAMEs in wastewater, which represents a loss of industrial profits. For the purpose of determination and monitoring of the FAME profile in wastewater, there is a necessity to develop a fast and reliable approach with small volume of sample in need. Hence, in this study, a combination of dispersive liquid-liquid microextraction (DLLME) and microwave demulsification is applied for the enrichment of residual FAMEs in water, followed by qualitative and quantitative analyses using gas chromatography-mass spectrometry. The results indicate that the optimal extractant in DLLME approach is toluene. And the optimal parameters are 20 mL of water sample, 80 mu L of toluene as the extractant, 60 s of ultrasonic irradiation duration, 200 W of microwave power and 2 min of microwave irradiation duration. The standard curves and linear equations obtained with these conditions are used for the quantitative analysis of biodiesel wastewater, which reveals that there was 50.35 mg.L-1 of the total FAME residuals in wastewater. To the best of our knowledge, it is for the first time that the combined technique of DLLME and microwave demulsification is applied in determination of residual FAMEs in water samples. The proposed method corresponds to small volumes of sample and extractant and short analytical period. It also has the potential to be extended to the analysis of other water pollutants.

Deep eutectic solvent has been gaining much attention in recent years due to its various novel properties. The present study develops a novel microwave-assisted hydrodistillation method based on pretreatment using deep eutectic solvent, for the extraction of essential oil (EO) from dry fruits of Amomum kravanh, Amomum tsaoko, and Amomum villosum, respectively. The process is optimized by single-factor experiments taking the improvement in the essential oil yield of A. kravanh as the target. The results indicate that using the reaction product of choline chloride and ethylene glycol as the deep eutectic solvent with 7:1 of mass ratio to fruit powder, the optimal conditions are (1) pretreatment stage: 500 W of microwave power, 50 °C of temperature, and 7 min of duration; (2) fast heating stage: 600 W of microwave power, 110 °C of temperature, and 5 min of duration; (3) hydrodistillation stage: 300 W of microwave power, 110 °C of temperature, and 30 min of duration. Under these conditions, the EO yields of A. kravanh, A. tsaoko, and A. villosum are 3.64, 2.16, and 1.62%, respectively. The EOs are analyzed by gas chromatography–mass spectrometry, with totally 63 compounds identified. In most cases, the new method brings about more identified compounds than the traditional methods. Moreover, the relative contents of hydrocarbons in most essential oils are improved by applying the new method. Thus, the approach based on deep eutectic solvent has been proved superior in the enhancement of essential oil production.

The MAD–DLLME method introduces microwave irradiation to achieve phase extraction, using a homemade glass flask as the extraction vessel.

A novel microwave-assisted-demulsification dispersive liquid-liquid microextraction technique was established for determination of three triazole fungicides in environmental water samples by gas chromatography with mass spectrometry. Importantly, microwave irradiation has been applied in demulsification to achieve the phase separation and enrichment of triazole fungicides in water samples successfully with low-density toluene as extractant. The experimental variables, including microwave power, microwave time, ultrasonic time, type and volume of extraction solvent, and effect of salting out were investigated. Under the optimized conditions, the method showed good linearity for myclobutanil, tebuconazole, and difenoconazole in the range of 1-100 mu g/L. The limits of detection and the limits of quantification were within the range of 0.14-0.27 and 0.47-0.90 mu g/L, respectively. The suitable enrichment factors for three triazole pesticides were in the range of 425-636. The recoveries were between 89.3 and 108.7%, and the relative standard deviations were from 5.4 to 8.6%. Finally, environmental water samples were used to verify the applicability of the proposed method for analysis of triazole fungicides targets. It can be concluded that the developed microwave-assisted-demulsification dispersive liquid-liquid microextraction gas chromatography with mass spectrometry method was a rapid, efficient, reliable, and environmental friendly way for analysis of triazole fungicides in water.

Deep eutectic solvents (DESs) have been gaining much attention in recent years due to their various novel properties.

A novel method of microwave-assisted deep eutectic solvent extraction coupled with solid-phase microextraction was developed to determine the volatile compounds in tobacco by gas chromatography-mass spectrometry. During the process, the deep eutectic solvent played the roles of absorbing medium for microwave radiation, destroyer of cell walls, and solvent for dissolving the compounds released from the cells. Combined with solid-phase microextraction, the volatile components were extracted and concentrated in one step. In this method, several experimental parameters, such as fibre type, deep eutectic solvent type, microwave power, set-up temperature and irradiation time were studied. Compared with microwave-assisted water extraction coupled with solid-phase microextraction, and conventional solid-phase microextraction, more volatile components were obtained with higher responses. It was demonstrated that this method has improved extraction efficiency. Moreover, the proposed method has been applied to analyzing tobacco volatiles from different regions and nine different types of components have been detected. The results indicate that microwave-assisted deep eutectic solvent extraction coupled with solid-phase microextraction is an efficient, environmentally-friendly and fast miniaturization pretreatment technology for the extraction of volatiles from tobacco samples. This is a potentially promising technique for other complex and valuable matrices with low volatile content.