Exhaustive extraction of sulfonamide antibiotics from aged agricultural soils using pressurized liquid extraction

A pressurized liquid extraction (PLE) method was developed for the quantification of five sulfonamide antibiotics (sulfadiazine, sulfadimethoxine, sulfamethazine, sulfamethoxazole, and sulfathiazole) in aged soil samples. To account for sequestration effects the extraction was optimized using a composite grassland soil sample collected 11 days after the application of manure containing these substances. The optimized method uses a mixture of buffered water (pH 8.8) and acetonitrile (85:15) as solvent for the extraction at 200 degrees C and 100 bar during five min. The most important parameter for the extraction efficiency was temperature whereas the pH of the extraction solvent did hardly influence extraction efficiency between pH 4.1 and 8.8. A temperature increase from 100 to 200 degrees C improved the extraction efficiency up to a factor of six for aged residues in soils. In contrast, no temperature dependence was observed during short-term spike experiment. After 90 min exposure in these spike experiments we recovered 62-93% of the sulfonamides, except for sulfamethoxazole with only 41%. These percentages decreased substantially after a contact time of 6 and 17 days. The reasons for this decline remained unknown. Inter-day precision of the method was very satisfactory: relative standard deviations from the average were below 10%. Limits of detection for the extraction procedure were lower than 15 microg/kg. The performance of the developed extraction method was demonstrated by measuring the decrease of sulfonamide concentration in a top soil after manure application. Within 3 months the concentration of sulfadiazine dropped from 450 to 150 microg/kg.