Enantioselective analysis of chloramphenicol residues in honey samples by chiral LC-MS/MS and results of a honey survey

ABSTRACT

Chloramphenicol (CAP) is a broad-spectrum antibiotic used widely in both human and veterinary medication. Since 1994, CAP has not been authorised for use in food-producing animals in the European Union due to several adverse effects. A minimum required performance level (MRPL) of 0.3 µg kg^–1 was established in 2003. The CAP molecule contains two asymmetric centres, thus in total four para-CAP stereoisomers exist. Only the RR-CAP enantiomer is bioactive, having significant antimicrobial activity. For the first time a chiral LC-MS/MS method is reported to identify and quantify the four CAP enantiomers at residue levels in honey samples. The method was validated at two concentration levels. The decision limits (CCα) and detection capabilities (CCß) were well below 0.3 µg kg^–1, with limits of quantification (LOQs) between 0.08 and 0.12 µg kg^–1 for all four enantiomers. The method provides a sensitive and reliable analysis of CAP enantiomers in honey, and proved its robustness during the daily routine analyses of numerous honey samples. In an internal honey survey, in total 40 honey samples from different geographical regions with identified CAP residues at or above the MRPL were reanalysed by chiral LC-MS/MS. In nine honey samples only the bioactive RR-CAP was detected as anticipated. However, in all other 31 honey samples the non-bioactive SS-CAP was also identified and quantified unambiguously. In 10 of these samples, mixtures of RR- and SS-CAP were analysed, and in 21 samples only the SS-CAP enantiomer, with concentrations up to 2.2 µg kg^–1. Most of these samples are honeys from Ukraine and Eastern Europe. This is the first report of SS-CAP residues in food samples. The potential sources for these findings are discussed and the need of further systematic studies emphasised. It is recommended to examine in more depth the toxicological profile of the individual CAP stereoisomers.

KEYWORDS:

• Chloramphenicol
• stereoisomers
• enantiomers
• 1R,2R-p-chloramphenicol
• 1S,2S-p-chloramphenicol
• enantioselective analysis
• chiral LC-MS/MS
• chiral separation
• honey
• residue analysis

Acknowledgments

The authors thank Martin Linkogel and Caterina Hünniger for initiating this project. They also thank Katja Bohm for the diligent pollen analysis of the honey samples; as well as Jantje Koch and Kirsten Leopold for the skilful sample preparation. Diedrich Harms is gratefully acknowledged for the critical review of the manuscript; and Sandra Meixner for the continuous support of this study. Furthermore, they thank Katharina Schlüter, Marcus Rummler and Roland Kallenborn (Norwegian University of Life Sciences, Ås, Norway) for helpful discussions and documents.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was not funded by any entity or organisation.