## 4 Discussion
Moreover, other extraction methods have been reported for analyzing chloramphenicol [17], MG, and LMG [18]. In addition, we applied this method for the extraction of chloramphenicol, MG, and LMG residues in bivalve samples [5]. The method used herein was developed for the simultaneous detection of chloramphenicol classes, quinone classes, MG, and LMG in shrimp samples. This is the most efficient and energy-conservative method for veterinary drug extraction. However, the same method could not be employed to analyze the nitrofuran metabolite residues in aquatic samples; because of their chemical structural characteristics, nitrofuran metabolites in food samples were extracted using 2-NBA for derivatization [19]. To validate the shrimp sample analysis method, as recommended by the TFDA [11], the acceptable recovery rate had to be 70-120% with RSD \(<\) 15% for chemical residues in food matrixes detected in the 0.1-1 mg/kg range; 70-120% with RSD \(<\) 20% for those detected in the 0.01-0.1 mg/kg range; 60%-125% with RSD \(<\) 30% for those detected in the 0.001-0.01 mg/kg range; and 50-125% with RSD \(<\) 35% for those detected within \(\leq\)0.001 mg/kg. According to our results, veterinary drug residues detected within \(\leq\)0.001 mg/kg and 0.001-0.01 mg/kg ranges demonstrated a recovery rate of 80-120% with an RSD of \(<\)10% and a recovery rate of 70-120% with an RSD of \(<\)15%, respectively. The TFDA also recommends various LOQs, including 0.3 ng/g in chloramphenicol; 5 ng/g in florfenicol and thiamphenicol; 10 ng/g in quinolone classes; 0.5 ng/g in MG and LMG; and 1 ng/g in nitrofuran metabolites, for aquatic food for the assessment of veterinary drug residues in seafoods [20]. Compared with the LOQs recommended by the TFDA, the LOQs obtained using our analytical method were lower and can be employed to detect trace veterinary drug residues. Therefore, the analytical methods employed herein conform to the recommendations of the TFDA. The regulations entitled Tolerances for Residues of Veterinary Drugs in Food, established by the Ministry of Health and Welfare of Taiwan, state that nitrofuran metabolites, chloramphenicol, MG, and LMG are banned from use in shrimp culturing because of concerns that pertain to mutagenicity and carcinogenicity [5]. In addition, food-producing animals and products containing these chemicals exported by third-world countries are prohibited in Japan and the European Union, the major importers of Taiwanese marine products. Based on methodologies available for detecting banned compounds in edible products, the Department of Health of Taiwan [21] and EU Commission [22] have both established a maximum residual permissible limit (MRPL) of 1 ng/g for each nitrofuran metabolite in aquaculture, marine, and poultry meat products. Furthermore, the EU Commission stipulates an MRPL of 0.3 ng/g for chloramphenicol and 2 ng/g for MG plus LMG [16] in all food products of animal origin to ensure that customers worldwide are given the same level of protection. According to the aforementioned guidelines, the LOQs of our methods executed for identifying the levels of chloramphenicol, dye, and nitrofuran metabolite residues in shrimp meet the MRPL. The chromatography-mass spectrometry screening of carcinogenic antimicrobials--such as nitrofuran metabolites, chloramphenicol, MG, and LMG--in 53 shrimp samples demonstrated a positive result, with the chloramphenicol concentration being greater than the MRPL of chloramphenicol set by the EU Commission (0.31 ng/g in a grass shrimp sample). Administering chloramphenicol to food-producing animals is banned in Taiwan. Some aquaculture farmers use chloramphenicol regardless, however, because it is a broad-spectrum, inexpensive, and readily available antibiotic [23]. Mixed breeding has caused chloramphenicolicol to be employed for the prevention as well as treatment of infectious diseases in shrimp. In the present study, the proportion of positive identification of banned veterinary drugs was 1.89% (1/53).