A new screening method for the search for nitrofurans in feed and drinking water by LC-MS/MS

Nitrofurans are a class of synthetic antimicrobial compounds, active against both Gram-positive and negative bacteria. Their use in food-producing animals has raised concerns due to their potentially harmful effects on human health, such as carcinogenicity, mutagenicity, allergies, and development effects on fetuses and young children. Residues of nitrofurans in animal products, such as meat, poultry, eggs, and milk, can pose a risk to consumers if ingested. Therefore, regulations and monitoring programs have banned their use in food-producing animals and established to control the presence of nitrofurans in food products. In the Italian national official control plan on animal feed (P.N.A.A.), nitrofurans are among the prohibited substances which cannot be present in feed or drinking water. The objective of this work was to develop and validate a screening method for the detection of nitrofurans (NF), such as furaltadone, nitrofurazone, nitrofurantoin, and furazolidone, in animal feed and drinking water using LC-MS/MS. The feed samples are extracted with acetone, suitably diluted, and finally subjected to analysis by liquid chromatography combined with a mass detector (LC-MS/MS). The drinking water samples are filtered, acidified with formic acid, and analyzed by LC-MS/MS. To verify specificity, 20 blank feed samples and 20 blank drinking water samples were analyzed. The samples were kept at room temperature for the period necessary for the tests. The method has a detection capability (CC) of 0.5 mg/kg for feed and 1 µg/L for drinking water samples. The CC was verified, according to Reg. 808/2021, by the analysis of 20 blank feed samples and 20 blank drinking water samples spiked with nitrofurans. The robustness to slight changes was evaluated by taking into consideration the only important and critical variable i.e., the acidity, in terms of concentration of formic acid in the standard reading pool and in the sample solutions, considered an indispensable factor to obtain the maximum sensitivity response and good chromatography (Gaussian peaks). From the tests carried out, it has been demonstrated that slight changes in this chemical feature do not generate significant variations, i.e., they have no effect on the performance of the method. Based on the results obtained from the validation, the method is judged suitable for the qualitative screening of nitrofurans in feed and drinking water. It is fast, easy, and implies the analysis of multiple molecules at the same time.