Study On The Determination Of Aflatoxin M₁in Milk And Ochratoxin A In Vegetable Oils

In recent years, food safety issues result from biotoxin contamination have attracted much attentionwith the increasing occurrence of food safety problems. For example, the levels of aflatoxin M₁（AFM₁）in milk and ochratoxin A （OTA） in vegetable oils are always over the maximum limit. AFM₁, a kind ofcarcinogenic compound found in dairy products, such as milk and powdered milk can threat people’shealth. OTA, a kind of highly toxic compound threaten kidney and liver, which could be detected inagriculture products, such as cereals, legumes, and vegetable oils. In order to ensure food safety, it isvery important to develop method of determination of AFM₁in milk and OTA in vegetable edible oils,which play a key role in protection safe consumption of agricultural product quality and in promotingthe development of relative science.Based on high performance liquid chromatography and adopted on-line solid phase extraction topurification for the milk sample, the milk samples were detected by direct injection. The mainparameters of on-line solid phase extraction were researched. Loading, transferring, detecting andwashing-equilibrating conditions of aflatoxin M₁were also confirmed. The recovery, precision, accuracy,and sample determination were researched. Finally, an on-line solid phase extraction-high performanceliquid chromatography was established to determine the aflatoxin M₁in milk. The extraction enrichmentmaterials of OTA were fabricated, the OTA in vegetable oils was extracted and purified by the magneticsolid-phase extraction; several main parameters, which can affect the extraction efficiency werediscussed; the type and volume of desorption solvent, desorption time and the amount of extractionenrichment materials were studied; the recovery, precision, accuracy and sample determination of OTAwere researched. Finally, the magnetic solid-phase extraction based on graphene oxide for determinationof OTA in vegetable oils was established.Main conclusions were as follows.1. Study on the determination of AFM₁in Milk: SB-C18column and C18reversed phase columnwere chosed as the solid phase extraction column and the analytical column, respectively the on-linesolid phase extraction system was established, and the SPE column and analytical column could beswitched.The entire analysis process included sample loading, transferring, detecting andwashing-equilibrating; the analysis determination and washing-equilibrating of SPE column could beperformed simultaneously. In the transferring process the SPE column and the analytical column werein series, AFM₁was eluted from SPE column to analytical column. At the optimum condition, water andacetonitrile-water （20/80, V/V） as the loading solution of sample and the transfer mobile phase,respectively, the transfer flow rate was set at1.0mL/min; and the transfer time took2.5min. Thedetermination mobile phase was acetonitrile-water （15/85, V/V）, the leaching balanced mobile phase ofSPE column were water and acetonitrile-water （15/85, V/V）. The linear regress equations of AFM₁wasY=2.5275X-0.067; the correlation coefficients was0.9991; the limit of detection （S/N=3） of AFM₁was0.04μg/kg; the limit of quantification （S/N=10） was0.1μg/kg; the spiked recoveries in milk was in therange of98-105.7%; the relative standard deviation （%RSD） was in the range of0.79-2.56%. The results showed that the method with short cycle and good reproducibility was simple in operation. Themost important was that the automated determination of AFM₁in milk can be achieved by this method.2. Study on the determination of ochratoxin A in vegetable oils: through the preparation ofgraphene oxide and hydroxylated iron oxide materials, the≤1000rpm speed of graphene oxidematerial was selected and was combined with hydroxylated iron oxide into the magnetic graphene oxidefor extraction enrichment material of OTA. The OTA in vegetable oils was extracted and purified by themagnetic solid-phase extraction technology. At the optimum extraction conditions of OTA: thedesorption solvent was chosed as methanol; the time of desorption was1.0min; the volume ofdesorption solvent was1.0mL; the amount of extraction material was2.5mg. The linear regressequations of OTA was Y=5.9631X+0.027; the correlation coefficients was0.9993; the limit of detection（S/N=3） was0.3μg/kg; the limit of quantification （S/N=10） was1.0μg/kg; the spiked recoveries inedible vegetable oils was in the range of101.51-115.33%; the%RSD was in the range of3.02-4.28%.This method has some merits, such as, the simplicity of operation procedure, the effectivityof thesample purification, and the short period for detection of analyte. The method will play an importantrole in detection OTA in vegetable oils.