Determination of streptomycin and dihydrostreptomycin in milk and honey by liquid chromatography with tandem mass spectrometry.

Two liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods were developed for the determination of streptomycin (STR) and its derivative dihydrostreptomycin (DHSTR) in milk and honey. These aminoglycoside antibiotics are used as veterinary drugs. In the EU, the presence of dihydro- and streptomycin residues in honey is forbidden, the maximum residue level (MRL) in milk is 200 microg/kg. The methods were optimised with regard to sensitivity and chromatographic efficiency, and validated by a procedure consistent with EU directive 2002/657. Average recoveries and accompanying standard deviations were satisfactory. The limit of quantification of STR was 2 microg/kg in honey and 10 microg/kg in milk, of DHSTR it was a factor two lower. The precision of the milk analysis was improved by using STR as the internal standard for DHSTR and vice versa. In a survey of 186 honeys available on the Dutch market, 26% of the honeys of foreign origin were positive for (DH)STR. This occurence rate was consistent with previous surveys, but lower concentrations were found.

Determination of residues of quaternary ammonium disinfectants in food products by liquid chromatography-tandem mass spectrometry.

A liquid chromatography-tandem mass spectrometry method has been developed for the determination of residues of alkylbenzyldimethylammonium, didecyldimethylammonium, didodecyldimethylammonium, and benzyldodecylhydroxyethylammonium compounds in various food matrixes. These quaternary ammonium compounds (QAs) are used in the food industry as disinfectants. According to the Dutch Food Law, the total mass (expressed as cetyltrimethylammonium chloride) of QAs in food products shall not exceed the legislative limit of 0.5 mg/kg. Samples were extracted by a simple salting-out procedure, using acetonitrile and sodium chloride; about 100 samples could be prepared and analyzed daily. Special care had to be taken to thoroughly homogenize samples and to avoid the use of contaminated labware. The method was validated by a procedure in compliance with EU Directive 2002/657. From the matrixes of ice cream and minced meat, recoveries of more than 95% with a relative standard deviation of about 3% were obtained by 3 different analysts (n = 54). Detection limits were in the low microg/kg range. The decision limit (CCalpha) was determined to be 0.55 mg/kg. Dairy and meat products, collected in The Netherlands, were analyzed (761 samples). In 1% of the meat samples, 2% of the ice cream and milkshake samples, and 24% of the whipped cream samples, the Dutch legislative limit was exceeded. Over 2000 injections could be performed on a single column without deterioration of the peak shapes or recoveries.