Preparation And Optimization Of Silver Colloids And The Study Of TLC-Dynamic Method

A combined method of thin layer chromatography and surface enhanced Raman spectroscopy(TLC-SERS)has been applied to detect adulterants in botanical dietary supplements(BDS).However,the sensitivity and stability of this method needs to be improved.In order to solve this problem,simple and convenient SERS active substrates were prepared and optimized and the TLC-Dynamic SERS performance based on these substrates were investigated.This study consists of two parts: 1)Firstly,classic “Lee” silver colloid was prepared,and the silver nanoshperes were re-dispersed in different media.Dynamic SERS performance,with phenformin hydrochloride on a TLC plate as the probe,of these colloids was studied to select the most suitable re-dispersion solvent.After adulterants in BDS were separated with a TLC plate and located under UV illumination,DSERS detection was successfully performed.2)We optimized experimental conditions of preparing silver colloid using DMF as a solvent by varying the reactants’ mass ratio and the reaction time,and got the preferred colloid which owned the strongest SERS enhancement.Then the sensitivity and stability of preferred DMF colloids were investigated and the optimal DMF colloid was used to detect antitussive and antiasthmatic drugs adulterated in BDS.Finally,the result was further verified by LC-MS.The results were as follows: 1)50% glycerol silver colloid was preferred as TLC-Dynamic SERS active substrate which owned the strongest SERS enhancement.2)The optimal testing conditions were determined by the TLC-Dynamic SERS performance of 50% glycerol silver colloid.Wherein,the silver colloid volume was 3 μL,laser power was 220 mW,integration time was 5 s,and the detection time was 120 s.3)TLC-Dynamic SERS detection method was established,which was used to detect antitussive and antiasthmatic drugs(diphenhydramine hydrochloride,benproperine phosphate and chlorphenamine maleate)adulterated in BDS,and corresponding LOD values were 0.01%,0.01%,0.005%.The sensitivity of the TLC-DSERS technique was 1-2 orders of magnitude higher than that of TLC-SERS technique.4)Experimental conditions of preparing silver colloid using DMF as a solvent were optimized by varying the reactants’ mass ratio and the reaction time,and the preferred colloid which owned the strongest SERS enhancement was obtained using phenformin hydrochloride as a probe.5)Time stability of DMF 2:1 colloid(optimized)was investigated,and the RSD of relative intensity of 10 consecutive SERS spectra was 1.5%,which was much stable than “Lee” silver colloid(RSD 48.1%).6)LOD values of diphenhydramine hydrochloride,benproperine phosphate and chlorphenamine maleate were 0.01%,0.01%,0.001% using DMF 2:1 colloid,and the sensitivity was 1-2 orders of magnitude higher than that of “Lee” silver colloid.7)Using DMF 2:1 colloid as active substrate,TLC-DSERS method was demonstrated with rapid analysis of real BDS samples and one sample adulterated with benproperine phosphate(BEN)was found.Finally,the obtained result was verified by LC-MS.In this study,TLC and Dynamic SERS were successfully combined to detect adulterants in BDS.The newly established TLC-Dynamic SERS method is simple,highly sensitive,and stable,which not only can be used to realize rapid on-site detection of adulterants in BDS,but also can provide a new method for the detection of drugs and pesticide residue.