Formaldehyde Residue Testing Assay in Anguilliformes Eel
WH Lin , HL Chan, QH Lin, YL Chen, YH Chen, RS Chen, SH Lee
Animal Drugs Inspection Branch, Animal Health Research Institute, Council of Agriculture,Executive Yuan
Abstract
The purpose of this study is to assess formaldehyde residue in eels and generate a
basis for setting withdrawal periods, which could be used for reference in reviewing regulated items
of aquatic animal drug. In the test, high performance liquid chromatography was applied to
determine formaldehyde residue levels at different time points before drug administration and after
drug discontinuation. The sample tested in our study was prepared by extracting with water and
20% sulfuric acid before centrifugation. Then 2, 4-Dinitrophenylhydrazine was added into the
supernatant for a 15-minute water bath at 60℃ for pre-column derivatization before analysis. The
results showed that the muscle formaldehyde recovery rates ranged from 89.8 - 110.1 % and the
liver recovery rates ranged from 104.8 – 109.7 %. The intra-assay of the muscle and liver relative
standard deviation (RSD) was 1.36 – 3.10 % and 2.61 – 4.44 % respectively, and the inter-assay
was 1.37 – 7.28 % and 1.21 – 3.23 % respectively. The lowest detectable limit was 0.02 μg/mL and
the lowest limit of quantification was 0.08 μg/mL. The tests of this study followed the procedures of
residue testing for new veterinary medicine on fish and animals. Fish were dipped in low and high
formaldehyde doses of 25 and 50 mg/L respectively for a long time without a change of water. The
samples of muscles with skin and livers from the fish were collected on the day of the dip and on
the 1st, 2nd, 4th, 7th, 10th, and 14th day respectively prior to the dip. The results showed that the
residue levels in the muscles and livers of eel dipped in high dose of formaldehyde for one day were
both under the lowest detectable limit. The water (25±1℃) was examined after 48-hours dip and its
formaldehyde residue level was also under the lowest detectable limit.
Keywords: formaldehyde, high performance liquid chromatography, eel, residue testing.