Esi-qtof-ms coupled to hplc and its application for food safety  (Page 2/3)

As the interface between HPLC and MS, the ionization source is also important. There are many types and ESI and atmospheric pressure chemical ionization (APCI) are the most common ones. Both of them are working at atmospheric pressure, high voltage and high temperature. In ESI, the column eluent as nebulized in high voltage field (3 - 5 kV). Then there will be very small charged droplet. Finally individual ions formed in this process and goes into mass spectrometer.

Comparison of esi-qtof-ms and other mass spectrometer methods

There are many types of mass spectrometers which can connect with the HPLC. One of the most widely-used MS systems is single quadrupole mass spectrometer, whichis not very expensive, shown in [link] . This system has two modes. One mode is total ion monitoring (TIM) mode which can provide the total ion chromatograph. The other is selected ion monitoring (SIM) mode, in which the user can choose to monitor some specific ions, and the latter’s sensitivity is much higher than the former’s. Further, the mass resolution of the single quadrupole mass spectrometer is 1 Da and its largest detection mass range is 30 - 3000 Da.

The second MS system is the triple quadrupole MS-MS system, shown in [link] . Using this system, people can select the some ions, called parent ions, and use another electron beam to collide them again to get the fragment ions, called daughter ions. In other words, there are two steps to select the target molecules. So it reduces the matrix effect a lot. This system is very useful in the analysis of biological samples because biological samples always have very complex matrix; however, the mass resolution is still 1 Da.

The third system is time-of-flight (TOF) MS, shown in [link] , which can provide a higher mass resolution spectrum, 3 to 4 decimals of Da. Furthermore, it can detect a very large range of mass at a very fast speed. The largest detection mass range is 20 - 10000 Da. But the price of this kind of MS is very high. The last technique is a hybrid mass spectrometer, Q-TOF MS, which combines a single quadrupole MS and a TOF MS. Using this MS, we can get high resolution chromatograph and we also can use the MS-MS system to identify the target molecules.

Application of lc/esi-qtof-ms in the detection of quinolones in edible animal food

Quinolones are a family of common antibacterial veterinary medicine which can inhibit DNA-gyrase in bacterial cells. However, the residues of quinolone in edible animal products may be directly toxic or cause resistant pathogens in humans. Therefore, sensitive methods are required to monitor such residues possibly present in different animal-producing food, such as eggs, chicken, milk and fish. The molecular structures of eight quinolones, ciprofloxacin (CIP), anofloxacin methanesulphonate (DAN), enrofloxacin (ENR), difloxacin (DIF), sarafloxacin (SARA), oxolinic, acid (OXO), flumequine (FLU), ofloxacin (OFL), are shown in [link] .