HPTLC Screening Of 4 Chemical Hazards In Foods

Nowadays,methods based on conventional column chromatography linked to mass spectrometry was regarded as the“golden method”in many controlling laboratories.However,it was neither economically nor practically impossible to complete all analytical tasks with food safety relevance,directly by LC-MS or GC-MS.Facing this problem,a fast analysis method with high throughput,matrix-tolerance and enough sensitivity,precision and accuracy was highly desired.In the last years,remarkable advantages of high performance thin-layer chromatography(HPTLC)technology in food analysis attracted remarkable attention.Many application reports successful demonstrated that HPTLC analysis not only gave competitive precision and sensitivity,but more importantly showed ideal compatibility to emerging detections,which was impossible to conventional techniques.Therefore,research in the development of HPTLC based methods would substantially contribute to a stronger food safety framework.In light of this background,this research established and optimized methods combining HPTLC with fluorescence densitometry(FLD),surface enhanced Raman spectrometry(SERS),effect-directive derivatization and mass spectrometry.Meanwhile,using tyramine in cheese(exemplarily representing for endogenous toxin of manufacturing relevance),synthetic phenolic antioxidants in edible oil(exemplarily representing for hazardous residues of manufacturing relevance),illegal addition of Sudan Reds in fruit juice(exemplarily representing for food adulteration)and bates in tea(exemplarily representing for healthcare products adulteration)as model targets to evaluate the applicability and superiority of the established methods.The research content was consisted of following four parts:1)The first part presented a novel and facile method tailored for screening tyramine in cheese.Separation was performed on glass backed silica gel plates,using methanol/ethyl acetate/ammonia(6/4/1 v/v/v)as the mobile phase.Special attention were focused on optimizing conditions(substrate preparation,laser wavelength,eletrolyte types and concentrations)of surface enhanced Raman spectroscopy(SERS)measurements directly on plates after derivatization,which enabled molecule-specific identification of targeted bands.In parallel,fluorescent densitometry(FLD)scanning at 380</400 nm offered satisfactory quantitative performances(LOD=9 ng/zone,LOQ=17 ng/zone,R~2=0.9996 and RSD=6.7%).Including a quick extraction/cleanup step,the established method was successfully validated with different cheese samples,both qualitatively(straightforward confirmation)and quantitatively(recovery rates from 83.7%to 108.5%).Apart from that,the mechanism of electrolyte induced SERS enhancement was preliminarily studied in both electromagnetic fields coupling and chemical absorption directions.2)The second part presented a standardized screening method for two major phenolic compounds(butylated hydroxytoluene and tert-butylhydroquinone)added in edible oils as antioxidants.In order to specifically visualize the targeted compounds after developing with toluene/ethyl acetate/methanol 8:1:1 v/v/v on silica gel plates,to 70 mm migration distance,the plate was subjected to a standardized 1,1-diphenyl-2-picrylhydrazyl(DPPH)assay.In addition to synoptical eye-inspection,accurate quantification was realized by modified densitometric measurements:fluorescence mode,excitation wavelength 530 nm(D2&W lamp)without optical filter,which offered satisfactory sensitivity(8.5-17.5 mg/kg)and acceptable linearity(R~2>0.999 within 50-200 ng/zone).Moreover,the established method was validated with edible oil samples,against EU Directive 2006/52/EC.Apart from that,the unambiguous confirmation of positive results was conveniently achieved by TLC-MS interface mediated mass spectrometry.Featuring the merits of screening conception,the proposed method not only reached the goal of accurate quantification,but also conclusive identification of multi phenolic antioxidants,3)The third part presented a fast screening method for determining Sudan dye adulteration in grape juice,based on the combination of HPTLC and SERS.Chromatography separation was achieved on silica gel plates using petroleum/acetone/acetic acid(9/1/0.1,v/v/v)as the mobile phase.After that,key factors including silver nano particle concentrations,electrolyte types/concentrations and incident laser wavelength was investigated with regarding to their effects on the quality of SERS results.Under optimized conditions(10 fold concentrated AgNPs colloid,633 nm incident laser,0.5-1 mol/L NaCl),the method sensitivity reached to 0.01-0.05 mg/kg,while remarkable linearity(R~2>0.996)was obtained within the range of 1-20 mg/kg.More importantly,the established method showed satisfactory accuracy(spiking recovery rates 72%-104%)and precision(%RSD 4.5%-9.6%)in the validation with the grape juice sample,therefore suitable for screening illgeal colourants addition in food and beverage.Apart from that,the usability of SERS results as fingerprints for distinguishing structurally similar compounds was studied as well.4)The fourth part first explored the feasibility of combining a bioluminescence bacteria(Vibrio fischeri)with HPTLC for bates detection;meanwhile,the mechanism of different layer materials on biosensing capacity of bacteria cells was preliminarily investigated and elucidated.According to the principle of similar compatibility,targeted compounds that were hydrophobilic was anchered by propanol amine groups.Therefore the molecules of analyte were not able to difuse into bacteria suspension after dipping.As the result,they were difficult to be exposed to bacteria cells,which may account for the low sensitivity on amino silica gel layers.On this basis,a facile method for simultaneously screening two bates(benzafibrate and ciprofibate)adulteration in a large array of teas was established.More specifically,tea extracts was firstly separated on silica gel plates with ethyl acetate-methanol(9/1,v/v)as the mobile phase;then,bacteria suspension was coupled with chromatographic results by dipping;under optimized conditions,8 min exposure offered satisfactory detection sensitivity;in addition,the bioluminescent inhibition patterns in graphic form was digitalized into computable chromatogram,based on which high precise results(recovery rates 71-91%)can be obtained easily.In summary,the featuring superiority of HPTLC based food analysis is not just because of its high throughput capacity,separation efficiency and low cost-effectiveness ratio.More importantly,HPTLC offers an ideal platform easily but efficiently combining chromatographic results and advanced detectors,therefore displaying promising prospective in the field of food analysis...