Reference standards for the nitrofuran drug metabolites are available as stable isotope labelled compounds or unlabelled in methanolic solution
LGC Promochem has launched a range of reference standards for the nitrofuran drug metabolites.
Developed by Cambridge Isotope Laboratories, these new standards support the demand for analytical techniques to determine drug residues in meat. Nitrofurans are inexpensive and effective veterinary antibiotics that have been widely used for the treatment of gastrointestinal infections in cattle, pigs and poultry.
In 1995, following concerns about their potential carcinogenicity, they were banned from use in animals for human consumption that are either produced in, or imported into, the European Union (EU).
However, these drugs, which include furazolidone, furaltadone, nitrofurantoine and nitrofurazone are still manufactured and used on food producing animals in many places outside the EU.
During an investigation early in 2002, nitrofuran residues were found in seafood products from south-east Asia and subsequent further testing found residues in poultry, duck and rabbit imported from this region.
This rather worrying development prompted the European Commission (EC), in 2002, to insist on positive-release testing of all imported edible animal products from specified countries of origin for residues of nitrofurans and their metabolites.
This affected a major import market.
In March 2003, Portugal stopped the sale of all chicken, turkey and quail due to suspicions of nitrofuran contamination and smaller scale incidents have also recently occurred in Italy and Greece. Looking for residual parent drugs is not particularly effective in detecting their use, because they are metabolised within hours of administration.
However, protein bound metabolites such as AOZ (3-amino-2-oxazolidinone), AMOZ (5-methylmorpholino-3-amino-2-oxazolidinone), AHD (1-aminohydantoin hydrochloride) and SEM (semicarbazide hydrochloride), may persist for weeks or even months, and do not degrade significantly during cooking or processing.
These residues can be released from proteins under moderately acidic conditions and can be determined as total nitrofurans, or simply as bound residues.
Currently there are no immunochemical or microbiological screening methods available for detecting all four nitrofuran antibiotics.
In fact the only analytical technique that is really effective in meeting the EU's criteria for sensitivity and confirmation of identity is LC-MS/MS.
Recently, however, a liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) method has been developed, and this is capable of simultaneous determination of the metabolites of all four nitrofuran drugs in meat and meat products.
In this method, sample clean-up and analyte enrichment are carried out by extraction with ethyl acetate, hydrolysis of the protein-bound drug metabolites, and derivatisation with 2-nitrobenzaldehyde (2-NBA).
In trials, at least two precursor-product transitions were measured for each metabolite, and each measured decision limit was below the EC's minimum required performance level of 1g/kg.
The new standards are available as stable isotope labelled compounds with deuterium or carbon-13 and nitrogen-15 or unlabelled in methanolic solution.
