β-agonist, as one kind of chemosynthetic phenylethanolamines, was mainly used for the prevention and treatment of bronchial asthma and spasm for humans and animals at early stage, and it was later found that the fodder with this additive has an important function in nutrient redistribution and can significantly improve the lean percentage of animals, as a result, it has been abused by some unscrupulous farmers, resulting in substantial residue in animal tissues. As the β-agonist remains and accumulates in the edible tissues of animals, people who eat these animals will have toxic reactions, which are harmful to the health, and even endanger the safety of life. The enzymelinked immunosorbent assay is a rapid detection method of β-agonist, which easily leads to false positive or false negative, while the high performance liquid chromatography has a relatively low sensitivity, thus it is easy to be interfered by complex matrixes. In this paper, the SPE-GC/MS method is used to detect the residues of four kinds of β-agonist in animal tissues.
Condition the PCX cartridge with 5 mL methanol, 5 mL of deionized water and 5 mL of 30 mM HCl solution sequentially.
Load sample concentrate onto the cartridge.
Wash the loaded cartridge with 5 mL water followed by 5 mL methanol, and discard the eluate.
Dry the cartridge by passing through nitrogen gas.
Elute the cartridge with 5 mL methanol containing 4% ammonia, and collect the eluate into a glass test tube, and then dry the eluate at 50 Celsius under a gentle flow of nitrogen (ca. 1 mL/min).
Derivatization and Detection
Heat the sample tube in an oven at 50 Celsius for a few minutes to remove water. Add 100 μL of toluene and 100 μL of N,O-Bis (trimethylsilyl) trifluoroacetamide (BSTFA) to the test tube. Vortex mix for 20 s. Seal the test tube and place it in oven at 80°C for 1 h. Cool and add 300 μL of toluene to the test tube. The solution is ready for GC-MS analysis (GC column: DA-5MS, 30 m×0.25 mm×0.25 μm, P/N: 1525-3002).
Results and Discussion
Samples of pig liver, spiked with 1, 2, 5, 10, and 100 μg/L, respectively, were extracted by liquid-liquid partitioning. Four batches of samples were tested. In each batch, 5 replications were used for each concentration. The results of the recovery test are listed in the following table.
Table 1 Recoveries and Precisions of analysis of pork liver samples
Table 2 Repeatability of analysis of pork liver samples
Figure 1 Typical total ion chromatography (TIC) of spiked pig liver samples at six concentrations: 0.5 μg/L, 1 μg/L, 2 μg/L, 5 μg/L, 10 μg/L and 100 μg/L: liver + 1 ppb (pcx)
In the concentrations of 0.5,1, 2, 5, 10 and 100µg/L, the overall average recovery rate is from 73.65% to 89.75%. As the method has a fast analytical speed, high sensitivity and good reproducibility, and the technical indexes are in line with the relevant laws and regulations at home and abroad, it can be used for the analytical detection of the residues of four kinds of β-agonist in animal derived food.