| Objective:In recent years,as a novel sample-pretreatment method,dispersive liquid-phase microextraction?DLPME?has been developed rapidly and used widely.It has some considerable advantages compared with other liquid-phase microextraction methods,such as large contact surface between extraction solvent and sample solution,short extraction time,low cost,and high enrichment factor?EF?.However,DLPME has some demerits as following:the collection of extractant droplet is difficult;centrifugation is required after extraction;the toxic extraction solvents are used frequently;large amount of disperser is used.Therefore,aiming at the existing problems,this paper improves it in the aspects of extraction solvent and extraction device so as to establish an environmentally friendly and more convenient DLPME method,and apply it to the determination of active components in traditional Chinese medicines.Methods:In part one of this paper,based on the conventional dodecanol floating solidification microextraction?DFSME?,we introduced the nanometer material-graphene and established the sample pretreatment method of graphene/dodecanol floating solidification microextraction?GDFSME?.In this work,graphene/dodecanol dispersion liquid and magnetic stirrer were employed as the extraction solvent and extraction power,respectively,caffeic acid,p-hydroxycinnamic acid,ferulic acid and cinnamic acid were used as model compounds.Through conditions optimization and methodology research,DFSME or GDFSME coupled with high performance liquid chromatography?HPLC?was applied to simultaneously extract,concentrate and determine four target compounds in traditional Chinese medicines.The proposed method was compared with other extraction methods of cinnamic acid derivatives,and the possible microextraction mechanism was analyzed and discussed.In part two of this paper,binary-solvent?n-pentanol and n-hexanol?and a disposable syringe were employed as extractant and extraction chamber,respectively,we proposed and established an in-syringe binary solvent liquid-phase microextraction?in-syringe BSLPME?only by manually shaking,which broke the conventional extraction mode of a single organic solvent.This method coupled to HPLC was applied for the enrichment and determination of cinnamic acid derivatives?caffeic acid,p-hydroxycinnamic acid,ferulic acid,and cinnamic acid?in traditional Chinese medicine samples.Several parameters affecting the performance and methodology research were optimized and investigated.Also,the proposed method was compared with other liquid-phase microextraction methods.In part three of this paper,a novel vortex assisted switchable solvent liquid-phase microextraction?VA-SSLPME?followed by HPLC was developed to extract and determine trace levels of four cinnamic acid derivatives?caffeic acid,p-hydroxycinnamic acid,ferulic acid,and sinapic acid?in traditional Chinese medicines samples.In this method,a switchable solvent-hexanoic acid was used as extractant to replace the toxic organic solvents,and dynamic vortex mixing was employed as auxiliary power.The extraction conditions and methodology were optimized and investigated,the enrichment factors of target compounds were calculated,and the extraction mechanism was clarified.Results:?1?In part one of this paper,under the optimised extraction conditions,EFs of four target analytes for DFSME and GDFSME were 14-61 and 26-112,respectively;extraction recoveries were 8.4%-36.6%and 18.2%-78.4%;the linear ranges were 1.0×10-2-10.0?g/m L for caffeic acid,1.25×10-3-1.9?g/mL for p-hydroxycinnamic acid,2.8×10-3-4.1?g/m L for ferulic acid,and 2.7×10-3-4.1?g/mL for cinnamic acid;the correlation coefficients?r2?of two methods were 0.9990-0.9999 and 0.9993-0.9998,their detection limits were 0.2-2.0 ng/mL and 0.1-1.0 ng/mL,limits of quantitation were 0.8-6.0 ng/mL and 0.5-4.0 ng/mL;relative standard deviations?RSD?of intra-day precision were1.6%-8.8%and 1.1%-8.8%,and inter-day precision were 3.9%-9.5%and 4.0%-9.5%;average recoveries were 90.2%-108.8%and 92.5%-111.2%,respectively.?2?In part two of this paper,after optimization of extraction conditions,EFs of target analytes for in-syringe BSLPME were 14-61;extraction efficiencies were 49.0%-101.5%;linearities of caffeic acid,p-hydroxycinnamic acid,ferulic acid,and cinnamic acid were found to be1.0×10-2-7.0?g/mL,1.25×10-3-1.9?g/mL,2.8×10-3-4.1?g/mL,and 2.7×10-3-4.1?g/mL,respectively,with r2 ranged from 0.9912 to 0.9974;the limits of detection were 0.2-1.3ng/mL,the limits of quantitation were 0.5-4.0 ng/m L;RSDs of intra-day precision and inter-day precision were 1.4%-9.4%and 2.2%-9.6%,respectively;average recoveries ranged from 94.2%to 106.7%.?3?In part three of this paper,under the optimised extraction conditions of VA-SSLPME,EFs of target analytes were 7-57;the calibration graphs were linear in the range of 1.0×10-2-6.0?g/m L for caffeic acid,5.0×10-3-2.0?g/mL for p-hydroxycinnamic acid,and 1.5×10-2-4.0?g/mL for ferulic acid and sinapic acid,with r2 ranged from 0.9949 to 0.9999;the limits of detection were 2.0-7.0 ng/m L,the limits of quantitation were 5.0-20.0 ng/mL;RSDs of intra-day and inter-day precision were1.4%-8.1%and 1.8%-8.8%;average recoveries ranged from 99.3%to 110.0%.Conclusion:In this paper,three novel microextraction methods of GDFSME,in-syringe BSLPME,and VA-SSLPME were developed.Compared with conventional dispersed liquid-phase microextraction method,they had many advantages,such as simple operation,wide application range,low cost,environment-friendly,high EF,and the three methods combined with HPLC were successfully applied to simultaneous extraction,concentration and determination of trace levels of cinnamic acid derivatives in traditional Chinese medicine samples. |
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