| Antibiotics are widely used in animal husbandry because of inhibiting or killing pathogenic bacteria,which are play an important role in animal disease prevention and control,improving feed utilization,and promoting the growth of livestock.However,with the extensive use of antibiotics,especially the unscientific abuse and non-compliance with the expiration period,etc.,the problems of bacterial resistance and drug residues have become increasingly serious.Therefore,it is of great significance to develop accurate,rapid,and sensitive analytical methods for the determination of antibiotic residues in foods.In this study,with antibiotics as target analytes,two solid-substrate electrospray ionization mass spectrometry techniques were used to rapid determination of various antibiotic residues in milk and honey.Firstly,qualitative and quantitative detection of 24antibiotics in milk was carried out by paper spray mass spectrometry(PS-MS).The effects of various parameters on PS-MS were investigated,and the rapid qualitative and quantitative analysis of multiple antibiotic residues in milk was realized.Considering the severe matrix interference in food samples,a surface molecularly imprinted polymer(MIP)solid-phase microextraion(SPME)probe was prepared to improve the sensitivity of the method.Rapid and high sensitive analysis of five macrolide antibiotics in honey and milk was successfully achieved using MIP probe electrospray ionization mass spectrometry(ESI-MS).The specific research contents and results are as follows:1.A PS-MS method was developed for rapid screening of 24 antibiotic residues in dairy products.In this method,milk was directly dropped onto the tip of the triangular paper without any sample pretreatment.A high voltage was applied to the paper base,and then a small amount of spray solvent was added to desorb and ionize the analytes for PS-MS analysis.The experimental parameters affecting the ionization process of antibiotics by PS-MS were optimized,including ionization mode,spray voltage,desorption solvent,etc.After optimization,the optimal experimental conditions were as follows:positive ion mode,+4.0k V of voltage,and 1%formic acid in methanol as desorption solvent.Qualitative analysis was carried out by comparing the accurate mass measurments and MS/MS fragment ion information of the analytes to those with the standard substances,and quantitatively analysis was performed using the ratio of the target analytes to the corresponding internal standard ion response intensity.The results showed that under the optimal experimental conditions,24 antibiotics have good linearity in the range of 0.5-100 mg/L,the correlation coefficient(r~2)were>0.90,the limits of detection(LODs)were 0.1-0.8 mg/L,and the limits of quantification(LOQs)were in the range of 0.3-2.0 mg/L.The average recoveries of the spiked sample were in the range of 74.1%-94.6%,the reproducible RSDs were less than 9.9%,and the reproducible RSDs were below 14.8%.The method is rapid and easy to operate,and could be used to simultaneously screen multiple antibiotic residues in dairy products.2.A MIP-SPME probe for specific adsorption of five macrolide antibiotics with similar structures was prepared by surface imprinting polymerization using wooden tip as substrate.The synthetic parameters such as functional monomer type,functional monomer addition amount and porogen were optimized in detail.The optimal synthesis conditions were:20 m L acetonitrile,0.0040 g roxithromycin as template molecule,100?L of methacrylic acid,200?L of ethyleneglycol dimethacrylate,20 mg of azodiisobutyronitrile,and polymerization for24 h.The probe before and after modification were characterized by infrared spectroscopy and scanning electron microscopy(SEM).SEM images showed that there were a large number of dense holes on the surface of the modified wooden tip.This structure provided an excessive contact area for the adsorption of analyte and improved the adsorption efficiency.Infrared spectroscopy scan confirmed the functional monomer methacrylic acid and crosslinker ethyleneglycol dimethacrylate were successfully polymerized on the surface of wooden tip.3.The MIP-coated wooden-tip was used as a SPME probe to directly extract five macrolide antibiotics of similar structures.The extraction parameters including extraction time,extraction volume,and p H values of extraction solvent were optimized.The optimal extraction conditions were as follow:40 min,100 m L,pH 5.0.Under the optimal extraction conditions,desirable enrichment capacity towards trace macrolide antibiotics in complex matrices were achieved,with the enrichment factors of approximately 244-1604 folds in pure water,72-370 folds in honey,and 12-44 folds in milk.The enrichment factors decreased with the complexity of the matrix,which indicates that the coating has poor resistance to matrix interference and needs to be further improved.4.A method for rapid analysis of trace macrolide antibiotics in honey and milk was developed by MIP-coated wooden tip ESI-MS.The sample after simple dilution was used for direct extraction,the MS data was recored in ion accumulation mode,and quantitative analysis was performed using the internal standard method.The results showed that the linear range of the five analytes in honey and milk was 10-1000 ng/g and 20-5000 ng/g,respectively,and the correlation coefficient(r~2)signal-to-noise ratio>0.99.The LODs of the five target antibiotics in honey and milk were 1.1-5.1 ng/g and 3.5-15.8 ng/g,respectively.The recovery test results ranged from 73.4%to 98.1%at two spiking levels,with a repeatibility RSD value between 5.7%and 10.7%,and a reproducible RSD value between 8.4%and 13.3%.The method has high sensitivity,good stability and rapid analysis,and could be used for qualitative and quantitative analysis of macrolide antibiotics in complex foods. |
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