GAS-CHROMATOGRAPHIC DETERMINATION OF CHLORAMPHENICOL RESIDUES IN SHRIMP - INTERLABORATORY STUDY

An interlaboratory study of a gas chromatographic method for determini ng chloramphenicol (CAP) residues in shrimp was conducted. An internal standard (I(std)), the meta isomer of CAP, was added to the shrimp, a nd the treated shrimp were homogenized with ethyl acetate. The ethyl a cetate extract was defatted with hexane, and the CAP was partitioned i nto ethyl acetate from an aqueous salt solution. The ethyl acetate was evaporated, and the dried residue was treated with Sylon, a trimethyl silyl derivatizing agent, to yield the trimethylsilyl derivative of CA P. A portion of the solution containing the derivative was injected in to a gas chromatograph equipped with an electron capture detector. Lev els of fortified and incurred CAP were calculated from the peak area r atio of standard CAP to I(std). Recoveries of CAP from tissue directly fortified at 5 ppb were 102% (within-laboratory relative standard dev iation [RSD(r)] = 5.6%),104% (RSD(r) = 5.5%), and 108% (RSD(r) = 6.3%) from Laboratories 1, 2, and 3, respectively. Incurred-CAP residues at 5 and 10 ppb levels were also determined, with the following results: Laboratory 1: composite A, 4.56 ppb (RSD(r) = 14.0%); composite B, 8. 38 ppb (RSD(r) = 11.6%); Laboratory 2: composite A, 4.17 ppb (RSD(r) = 12.5%); composite B, 8.90 ppb (RSD(r) = 5.60%); Laboratory 3: composi te A, 4.66 ppb (RSD(r) = 14.9%); composite B, 11.0 ppb (RSD(r) = 11.8% ).