Accurate Testing of Complicated Food Matrices

Worldwide food safety concerns have risen dramatically as the number of food contamination incidents and product recalls has increased. Accurately monitoring contaminant levels in food and agricultural products is essential to assure the safety of the food supply and to manage human health risks.

It is well-known that the basic analytical requirements in food analysis are high-resolution, high-throughput, high-sensitivity detection and quantification of contaminants at or below the maximum residue limit (MRL) or tolerance of the compound in a given food matrix. Liquid chromatography-mass spectrometry (LC/MS) as the central enabling technology has been recognized as an indispensable tool in the food safety and quality control fields.1 LC/MS provides high-speed, high-resolution, and high-sensitivity separation of various chemical compounds.

Every food analysis starts with sample preparation, widely accepted as one of the most critical steps of LC/MS. Increased demand for higher throughput and accuracy and lower matrix interference from food analysis laboratories has made sample preparation the largest bottleneck. Currently, solvent extraction and solid phase extraction (SPE) are two of the most commonly used methods to isolate and/or enrich target analytes from food matrices. Done manually, these offline techniques are often labor-intensive, time-consuming, and costly, resulting in low sample throughput. Turbulent flow chromatography technology can do away with the need for lengthy offline sample preparation steps, thereby eliminating these disadvantages.

Turbulent Flow Chromatography

This article will review a number of key applications in food safety using turbulent flow chromatography. All experiments used an LC/MS system (Thermo Scientific Aria TLX liquid chromatography system) powered by turbulent flow chromatography (Thermo Scientific TurboFlow technology) to separate analytes from various matrices prior to MS/MS analysis. The system injected the sample directly onto a narrow diameter (0.5 mm or 1.0 mm) chromatography column (the patented TurboFlow column) packed with large particles. High linear velocities are created inside the column, which force large molecules to flow quickly through to waste while retaining the small molecule analytes.

The technology is an improvement over traditional SPE because it uses reusable extraction columns in a closed system, reducing the time required for offline sample preparation from hours to minutes. It also allows automatic removal of proteins and larger molecules in complex mixtures by combining turbulence, diffusion, and chemistry. Shows the typical configuration of a single-channel TLX system.

By injecting food samples directly into the LC/MS system, which eliminates time-consuming and costly sample pre-paration steps, food safety and quality laboratories can achieve significant analytical improvements. Turbulent flow chromatography technology also allows the broad selection of stationary phases. These features make the technology a versatile and important tool in the food safety arena.

Applications in Food Safety

1) Veterinary drugs and chemicals: In recent years, there has been increased concern about the use of unauthorized veterinary drugs and other potentially hazardous chemicals in farming operations. The U.S., Canada, the European Union, and many other countries have either banned or limited the usage of many veterinary drugs involved in food production.

Four common chemical residues in fish, shrimp, and pig liver were analyzed using a triple stage quadrupole mass spectrometer (Thermo Scientific TSQ Quantum Access).2 Malachite green (MG), a triphenylmethane dye, is an effective and inexpensive fungicide used in aquaculture, particularly in Asian countries. The principle metabolite, leucomalachite green (LMG), has been shown to accumulate in fatty fish tissues treated with MG due to its longer retention time.

Ciprofloxacin is a synthetic, broad-spectrum antibiotic belonging to the fluoroquinolone group that is used to treat severe bacterial infections. Tetracycline is a polyketide antibiotic that is highly effective against a number of gram-positive and gram-negative bacteria. The MRLs for these analytes range from 2 µg/kg for the sum of MG and LMG residues in fish muscle to 100 µg/kg for both ciprofloxacin and tetracycline in muscle for all food-producing species.

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