LC–MS-MS Analysis of Malachite Green, Leucomalachite Green, Ciprofloxacin, and Tetracycline in Food Samples Using an Online TurboFlow LC–MS Method

The analysis of chemical residues in food requires techniques sensitive enough to detect and quantify contaminants at or below the maximum residue limit (MRL) of the compound in a given sample matrix. Because of increased food safety regulations and the growing numbers of samples to be analyzed, it is critical that the analytical techniques provide high sample throughput.

In this study, ciprofloxacin, tetracycline, and malachite green/leucomalachite green were examined in shrimp, fish, and pork liver. We show a solution that combines the Thermo Scientific Aria TLX system utilizing TurboFlow™ technology with a Thermo Scientific TSQ Quantum Access mass spectrometer. Compared to traditional offline extraction methods, this solution provides fast and reliable sample analysis of chemical residues in food by online sample extraction followed by LC–MS-MS. The Aria™ TLX system uses TurboFlow technology to retain small molecules and filter out proteins and larger materials by diffusion, size exclusion, and column chemistry. This enables users to directly inject samples into the LC–MS system for analysis, greatly simplifying sample preparation and increasing throughput.

MS Conditions

MS analysis was carried out on a TSQ Quantum Access™ triple stage quadrupole mass spectrometer.

Table I: Improvement in the TurboFlow method results over those of the standard HPLC results. Note that results are only shown for a compound in the matrix in which it would be found; for example, MG and LMG would be found in fish but not in pig liver.

Results and Discussion

The results of the assay and a comparison between standard HPLC method without any sample cleanup versus TurboFlow LC–MS method with online sample cleanup are shown in Table I. An example chromatogram is shown in Figure 1. Because the TurboFlow method removed matrix interferences, lower limits of detection (LOD) and lower limits of quantitation (LOQ) were obtained than in the standard HPLC method (see Table I). The corresponding percent relative standard deviation values (%RSD) were also improved, providing more confidence in the results. The limits of detection and limits of quantitation were well below the maximum residue limits for all of the substances.

Figure 1: Chromatogram comparison of tetracycline at 500 ng/kg in pig liver matrix in standard HPLC and TurboFlow method.

Conclusion

A rapid, sensitive and reliable method for the quantitation of veterinary drugs in food matrices was developed using the Aria TLX-1 system with the TSQ Quantum Access mass spectrometer. Minimal sample preparation was required because the TurboFlow method allows direct injection of samples into the system. The Aria TLX system reduced ion suppression and matrix effects compared to standard HPLC runs.

Thermo Fisher Scientific, Inc.

355 River Oaks Parkway, San Jose, CA 95134-1991

tel. (800)532-4752, fax (561)688-8731

Website: www.thermo.com