3.3. Accelerated Solvent Extraction (ASE)

ASE is an automated method for extraction with organic solvents under conditions of elevated temperature and pressure. Richter et al. [69] introduced ASE as a new extraction procedure that uses organic solvents to extract solids or semi-solids at higher pressures (500–3000 psi) and higher temperatures (50–200 °C). The advantages of the ASE method are the small amounts of organic solvents, high speed, low matrix effect, high recovery rate and good reproducibility, and it appears as the recommended method 3545 in update III of the US EPA SW-846 methods [70]. The ASE method is widely used to extract veterinary drug residues from animal-derived foods, and a brief flowchart of ASE sample preparation is shown in Figure 3. The animal-derived food samples are placed into a mortar and added to diatomaceous earth for grinding. After being fully ground, the sample is filled into a 22 mL stainless steel extraction cell, and then the lid is closed. The cell is placed on the ASE350 instrument, and the sample processing program is set.

Flowchart of accelerated solvent extraction procedures of animal-derived food samples.

Wang et al. [12] have developed a fast and sensitive ASE method coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) for the detection of spectinomycin and lincomycin in poultry eggs. This study used an ASE350 instrument and an Oasis PRiME HLB SPE cartridge to extract and purify egg poultry samples. The proposed method successfully detected spectinomycin and lincomycin with LODs and LOQs ranging between 2.3–4.3 μg/kg and 5.6–9.5 μg/kg, respectively. This method has a good correlation coefficient (R² ≥ 0.9991), recovery (80.0–95.7%) and precision (RSDs, 1.0–3.4%). Compared with the ASE-HPLC-MS/MS method [11], the ASE-SPE-GC-MS/MS method involves sample preparation steps that are complicated and require solid-phase extraction, which greatly increases the processing time. Tao et al. [71] used the ASE method to extract 17 MAC and avermectin residues in swine and bovine tissues (muscle, kidney, and liver) at 60 °C and 1500 psi for 10 min (static time) in two cycles, with ACN/methanol (1/1, v/v) as the extractant. After sample preparation, this study used the LC-MS/MS method to detect these analytes. The recoveries of the samples were all higher than 75%, and the LOD values were all lower than 0.55 g/kg. This study shows that ASE technology can extract multiple residues, which has advantages such as high speed, low consumption of reagents, and batch processing of samples.

Yu et al. [72] reported an ASE-HPLC-UV method for the detection of seven TCs in pig, chicken, and cattle tissues (muscle and liver). The LOD and LOQ values were lower than 10 μg/kg and 15 μg/kg, respectively. Within the range of concentrations used, the sample recovery was 75.0–104.9%, and the RSD was lower than 10%. A novel method was proposed by Wang et al. [11], who used an ASE350 instrument for sample pretreatment with methanol-ammonium hydroxide-ultrapure water (97:2:1, v/v) as the extractant. This study used HPLC-MS/MS to detect CAP, TAP, FF, and FF amine in poultry eggs. ASE extracts APs from poultry eggs to obtain a good extraction recovery rate, and the detection sensitivity of the method is relatively high (LOD values are all lower than 0.5 μg/kg). Compared with LLE and SPE methods, ASE has the advantages of simple operation, high speed, and batch processing of samples, greatly improving efficiency and saving time. With the development of sample preparation technology, the automated ASE method is worthy of promotion for the extraction of veterinary drug residues from animal-derived foods.