Identification of endogenous and exogenous semicarbazide (SEM) in crustacea aquatic products using compound-specific nitrogen stable isotope ratio analysis (NSIRA)

Endogenous SEM (SEMend) naturally occurs in crustacea aquatic products, it confuses the legal verdict of exogenous SEM (SEMex) degraded by antibiotic nitrofurazone abuse. In the present study, compound-specific gas phase chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) analysis coupled with a two-step pre-column derivatization was developed for determining the nitrogen stable ratio (δ15N) of SEM in shrimp and crab. The optimal derivatization and solid phase extraction (SPE) condition of SEM were screened by Plackett-Burman design and central composite design (CCD) experiment. The nitrogen isotope ratio analysis (NSIRA) of SEM in two types of crustaceans proved that its δ15N values significantly decreased from 7.0‰ to 2.0‰ once nitrofurazone being used. Analytical results found that the δ15N value of SEMex in vivo was consistent its nitrofurazone precursor but the value of SEMend was dependent on N-containing components (e.g., tissue protein), ANOVA showed significant difference between two types of SEM (p < 0.05). Based on the δ15N variations between SEM itself and its nitrofurazone precursor, tissue protein of crustaceans, the percentages of SEMex and SEMend can be calculated for its source apportionment in vivo. The limit of detection of SEM is down to 0.21 μg kg−1 and 0.54 μg kg−1, and the identification lower limit of SEMex are accurate at 6.27% and 0% for two types of crustaceans. The strategy first realized the independent determination of SEMex and SEMend in crustacea aquatic products, which explained that high-level SEM in crustaceans can’t as the legal verdict of nitrofurazone abuse in aquaculture.