Simultaneous determination of 20 veterinary drugs in grass carp by HPLC-MS/MS
This study establishes a simple and accurate HPLC-MS/MS method utilizing pass-through solid-phase extraction and isotope dilution for the simultaneous determination of 20 veterinary drug residues in grass carp, demonstrating good linearity, recovery, and precision.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Every time we eat a meal, our bodies are exposed to a complex world of chemicals, some natural and some introduced by human activity. In the world of aquaculture, farmers often use synthetic medicines to keep fish healthy and growing, much like doctors prescribe antibiotics for people. Among the most common of these medicines are fluoroquinolones and sulfonamides, two families of drugs designed to kill bacteria, along with a third agent called trimethoprim that helps them work better. While these treatments protect the fish, there is a genuine concern that if the drugs are not used carefully, tiny traces can remain in the meat we eat. These residues can accumulate in our bodies, potentially disrupting the delicate balance of bacteria in our gut or encouraging the growth of bacteria that no longer respond to medicine. To keep our food safe, governments around the world have set strict limits on how much of these drugs can remain in edible fish, creating a need for scientists to develop ways to find even the smallest amounts.
The challenge for scientists is that fish meat is a difficult environment to test. It is rich in proteins and fats, which can hide the drug residues or interfere with the machines used to detect them. Imagine trying to find a specific needle in a haystack that is also sticky and full of other debris; the tools used to pull out the needle might get clogged or confused by the hay. To solve this, researchers at the Shandong Freshwater Fisheries Research Institute in China focused on the grass carp, a fish that is widely farmed and eaten. They set out to create a single, efficient method to check for twenty different veterinary drugs at once, rather than testing for each type separately. Their goal was to build a process that could strip away the messy parts of the fish meat while leaving the drug traces behind, ready to be measured with extreme precision.
The researchers began by taking a small piece of the fish muscle and mixing it with a liquid solvent to pull the drugs out of the tissue. They found that a specific solvent worked best to dissolve the medicines while causing the fish proteins to clump together and separate out. To ensure the liquid was dry enough for the next step, they added a small amount of a drying salt, which soaked up any remaining water. The mixture was then spun at high speed to separate the solid bits from the liquid. The clear liquid, now containing the dissolved drugs, was passed through a special cartridge filled with tiny beads. This step acted like a filter that caught the unwanted fats and proteins but let the drug molecules flow straight through, effectively cleaning the sample without the need for complex washing or drying steps that usually take a long time.
Once the sample was clean, it was injected into a sophisticated machine that acts like a high-speed sorter and detector. The machine first separated the different drug molecules based on how they moved through a tube, and then it identified them by weighing their molecular fragments. To make sure the results were accurate, the scientists added a known amount of a "twin" version of each drug to the samples before testing. These twins are chemically identical to the real drugs but are slightly heavier, allowing the machine to distinguish between what was naturally in the fish and what was added for measurement. This technique allowed the researchers to correct for any interference from the fish meat itself, ensuring that the final numbers reflected the true amount of drug present.
The method proved to be highly effective. The researchers tested it by adding known amounts of the twenty drugs to clean fish samples and found that they could recover between 78.8% and 115.6% of the added drugs, with very little variation in the results. This level of accuracy meant the method was reliable enough to detect drugs at very low levels, well below the safety limits set by regulations. When the team applied this new method to real fish samples collected from farms across Shandong province, they found that while most of the drugs were absent, traces of two specific fluoroquinolones were present in some of the grass carp. The amounts found were low and within the legal safety limits, but their presence confirmed that the method could successfully spot these residues in a real-world setting.
This work provides a streamlined way for food safety inspectors to monitor a wide range of veterinary medicines in a single test. By simplifying the cleaning process and using a precise measurement technique, the researchers have created a tool that is both fast and accurate. This capability is essential for ensuring that the fish on our plates are safe to eat and that the use of medicines in aquaculture remains under control, protecting both human health and the environment from the risks of drug residue accumulation.
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