前言：

　　Ractopamine is a phenethanolamine member of the family of b2-adrenergic receptor agonists (b-agonists). It has been widely used as a veterinary additive drug in livestock production to promote leanness in meat, accelerate average daily weight gain and improve feed efficiency1. Recently, there have been growing concerns about the safety of meat containing ractopamine residues due to its potential health risks for humans2. Over 150 countries including China and the European Union (EU) have banned the use of ractopamine in animal feeds, but in other countries such as the US and Japan, ractopamine use is allowed. The maximum residue limit (MRL) of ractopamine has been set at 30 ppb for beef and 50 ppb

　　for pork in the US and 10 ppb for beef muscle by Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA)3. The EU also proposed 10 ppb as the minimum required performance limit (MRPL). Ractopamine has been a specific trade concern since a number of shipments of US beef containing trace level contamination were rejected by the Taiwanese government as early as 2007. Therefore, it is essential to develop a sensitive, reliable and effective analytical method for quantitative measurement of ractopamine in samples of animal meat and organs. A number of methods have been reported to monitor ractopamine residue in meatproducing animals using a combination of chromatographic techniques with mass spectrometry, including gas chromatography/mass spectrometry (GC/MS)5 and liquid chromatography/mass spectrometry (LC/MS). These approaches usually require complicated off-line sample clean-up procedures, primarily based on solid phase extraction (SPE), which can be very timeconsuming, labor-intensive and are vulnerable to variability due to errors in manual preparation.

仪器：

Thermo Scientific TSQ Quantum mass spectrometer

结论：

　　A quick, rugged, sensitive and automated online LC/MS method was developed to measure ractopamine in animal meat matrices. The TurboFlow method eliminates the need for time-consuming sample preparation procedures such as offline SPE, allowing for higher throughput and better reproducibility. The method quantitation limit has been determined to be 0.30 ng/g, which is significantly lower than the limits set by the US government and MRPL proposed by the EU. Owing to the large volume and/or multiple injection capability of Transcend TLX system11, the quantitation limit could be further lowered if necessary.

　　The relevant data window of this method represents only a part of total run time, thus sample throughput can be doubled or even quadrupled by multiplexing across a two or four channel Transcend TLX system. As a result, up to 40 samples per hour can be analyzed. There is also a potential to add other b-agonists, such as clenbuterol, into the same method.