OPTIMIZATION OF THE ANALYTICAL PERFORMANCE OF THE MAGNETIC-SECTOR MASS-SPECTROMETER FOR THE IDENTIFICATION OF RESIDUAL CHLORAMPHENICOL IN SHRIMP

Chemical noise limits mass spectrometric detection of chloramphenicol (CAP) with electron capture ionization at low resolution, and makes CA P identification at concentrations of 5 parts per billion (ppb) diffic ult. Increasing the resolution from 1000 to 3500, however, was suffici ent to separate the analyte signals from the noise signals, and result ed in a 100 times higher analytical sensitivity. The introduction of s weep gas in the ion source decreased the scattering of the quantitativ e results on average by a factor of 7, and thereby improved the precis ion of the analyses to an acceptable level (CV < 10%). Under such cond itions, CAP residues of 1.5 and 2.1 ppb in shrimp as determined by ele ctron capture gas chromatography/mass spectrometry can readily be iden tified by monitoring four diagnostic ions.