Food Screening Methodology Based On HPTLC Plus Strategy

Analytical methods based on “HPTLC plus” strategy has been frosting a new frontier in the field of analytical chemistry.HPTLC is a decentralized and open analysis system,completely different from the closed-loop operation principle of column chromatography.After the separation,all substances of the mixture stay on the chromatographic plate instead of the waste bottle.This featuring advantage enables HPTLC separation results to be easily coupled to many detection methods that are not compatible to traditional column chromatography systems.Therefore,HPTLC is not only a chromatography tool with high throughput,easy operation and high flexibility,but also can be used as a multi-functionalized platform,which has promising application prospects in food screening.In this work,HPTLC was applied as an integrated separation-analysis platform,which integrated multi-dimensional quantitative and qualitative techniques,including fluorescence densitometry,mass spectrometry,cell biosensor and surface enhanced Raman.Based on chromatography separation and optimization of detection parameters,the practicability and validity of HPTLC platform were verified through fluorescent whitening agent migration residues in cereal products,the residue of captan in fruits and adulteration analysis of chemical antihypertensive drugs in ginkgo tea.The main results were as follows:1.Using HPTLC as a platform to combine fluorescence densitometry scanning and in-situ mass spectrometry a rapid screening method was established for the migration of fluorescent whitening agent from package materials into cereal(rice and wheat)flours.The effects of mobile phase ratio,imaging conditions,matrix effects and scanning parameters on quantitative analysis were investigated,and the recovery and precision of the method were also determined.The results showed that the mixture of toluene/ethyl acetate(10.0/0.3,v/v)as the mobile phase can achieve complete separation of target molecules and interference matrix;fluorescence mode,mercury lamp,365 nm excitation wavelength and K400 filter were used as parameters to quantify the optical density of the images obtained.The scanning results of target spots after chromatographic separation showed a good linear relationship within the range of 200~2000 pg/zone(R2=0.9999);the standard recovery of wheat flour and rice flour was 78.5%~97.7%(RSD<4.5%).In addition,in-situ mass spectrum achieved reliable identification of target spots at the molecular level,further extending the practicality of the method.2.Using HPTLC as a platform to combine bioluminescence sensing,a rapid screening method was established for the pesticide residue of Captan in fruit samples.The effects of different layer materials(silica gel,NH2-silica gel,neutral alumina and acidic alumina),mobile phase ratio,and reaction time after immersion on quantitative analysis were studied,and the recovery and precision of the method were also determined.The results showed that the target molecule and the interference matrix could be completely separated using the silica gel plate as the stationary phase and a mixture of ethyl acetate/toluene(8/2,v/v)as the mobile phase;reacting for 4 min after immersing the bacterial solution,the inhibition of the targeted compound toward the bacteria bioluminescence reached the highest level and wasdocumented by Bio-visualizer.After taking the picture,the digitalized images of bioluminescence inhibition were captured through the professional software Videoscan.The results showed that the integral results of the target bioluminescence inhibition spots in the digital images displayed relatively good linear relationship in the range of 10~80 ng/zone(R2=0.9901)and its detection sensitivity was <10 ng/zone.Different fruits samples(apples,pears,apricots,plums,cherries and peaches)gave a standard addition recovery of75.0%~96.0%(RSD<11.8%).3.Using HPTLC as a platform to combined bioluminescence sensing with surface enhanced Raman spectroscopy,a rapid screening method was established for adulteration of the chemical antihypertensive drug nifedipine in Ginkgo tea samples.The effects of different layer materials(silica gel,cellulose,diatomaceous earth and polyamide),mobile phase ratio and reaction time after immersion on quantitative analysis were studied,and the recovery and precision of the method were also determined.The results showed that the target molecule and the interference matrix can be completely separated using a silica gel plate as the stationary phase and a mixture of toluene/ethyl acetate(8/2,v/v)as the mobile phase.After immersing the bacterial solution for 6 min,the nifedipine on the silica plate achieved the best imaging conditions about the bioluminescence inhibition of the bacteria;on this basis,combined with the pixel analysis function of software ImageJ,the obtained bioluminescence suppression images were quantitatively scanned.The results showed that the target spots had a significant linear relationship(R2=0.9985)in the range of 50~300 ng/zone;the standard addition recovery was 81.0%~92.8%(RSD<10.1%).While quantifying by pixel scanning,the use of Nano-silver sol substrate and 633 nm laser(He ? Ne,laser light source)achieved reliable identification and confirmation of the target spots at the molecular structure level.The obtained results evidenced that the open-source image analysis software can replace expensive optical density instruments and special software in HPTLC analysis,enhancing the flexibility and cost-efficiency of HPTLC for food analysis.