Electrochemical Analysis of Flavonoids by Nanomaterial Modified Electrode

Author:Li Xiao Bao

Supervisor:sun wei


Degree Year:2019





Flavonoids have many pharmacological activities,such as eliminating oxygen free radicals,anti-oxidation,anti-aging,anti-tumor,anti-virus,anti-bacterial,anti-radiation,anti-allergy,regulating blood lipids,estrogen-like activities and etc..Thus,they are widely used in medicine and act as the active ingredients of many drugs.Therefore,it is necessary to accurately and effectively analyze the concentration level of flavonoids in pharmaceutical preparations and biological body fluids,which is the key to the rational and effective application of flavonoids.Various methods including HPLC,GC and LC-MS have been developed during the past few years.However,these detection methods exhibit the disadvantages such as high detection cost,long time consuming and tedious operation steps in the process of practical applications,which seriously restrict their practical application.Electrochemical method has been used for flavonoids due to their characteristics of quick response,high sensitivity,as well as good selectivity.Also electrochemical reaction mechanisms can be investigated by various electrochemical techniques.The development of highly efficient electrode materials is the key to electrochemical methods.In this thesis,a series of research works had been carried out on the design and preparation of high-performance electrode materials with electrochemical analysis of flavonoids.By using rutin,luteolin and quercetin as the analytical targets,different functionalized nanomaterials such as gold nanocage,grapheme,ordered meso porous carbon,etc.had been used for the construction of high sensitive electrochemical sensing platform.Then the electrochemical behavior of these flavonoid drugs were checked with electrochemical parameters calculated,and new electrochemical procedure established.The major contents included as follows:1.A composite of GR and SnO2(GR-SnO2)was obtained through a hydrothermal reaction procedure.By coating GR-SnO2 onto the surface of carbon ionic liquid electrode(CILE),a modified electrode GR-SnO2/CILE was obtained and used as the working electrode.The electrochemical behavior of luteolin on the modified electrode GR-SnO2/CILE was studied by using electrochemical methods such as cyclic voltammetry(CV)and differential pulse voltammetry(DPV).The results showed that the measured current value was linearly correlated with the concentration of luteolin within 6.0×10-5to 6.0×10-2mol/L,with the detection limit of 9.8×10-99 mol/L(3σ).Also,this method was applied to the determination of the content of luteol in Duyiwei soft capsule sample with satisfactory results.2.Gold nanocages(AuNCs)were coated on CILE surface to obtain modified electrode(AuNCs/CILE).The TEM image illustrated that the AuNCs have hollow and porous structures,with rather thin walls.And the SEM images shows that AuNCs can maintain its own structures and morphologies even after it was modified on the surface of CILE.The electrochemical behavior of luteolin on modified electrode AuNCs/CILE was studied by electrochemical methods.The specific properties of AuNCs including large surface area was responsible for the enhancement of the electroanalysis performance,the DPV oxidation peak current showed a good linear relationship with the concentration of luteolin within1.0×10-91.0×10-6mol/L,with the detection limit of 4×10-10mol/L(3σ).This method was applied to the determination of the Duyiwei capsule sample with satisfactory results.3.A mesoporous carbon material was obtained through a pyrolysis procedure by using polyvinyl pyridine and ferric chloride as the precursors with SBA-15 as the template.The SEM and TEM image demonstrated that the morphologies of the as-prepared carbon material were similar to that of SBA-15 templates,with nanobar-like morphologies.The electrochemical test results indicated that rutin had an excellent electrochemical response on the surface of modified electrode.The DPV results showed that when the concentration of rutin was between 1.0×10-9and 1.0×10-5mol/L,the peak current measured was linearly related to the concentration of rutin in the solution.The detection limit of the electrode was calculated as 3.0×10-10mol/L(3σ).In addition,this modified electrode also exhibits excellent reproducibility and stability,which was applied to the determination of rutin tablets samples successfully.4.Phthalic anhydride,ferrous chloride and urea were used as the precursor and SBA-15as the templates to fabricate an ordered mesoporous carbon.The obtained carbon was characterized by using UV-VIS spectra,XPS,SEM,TEM and BET.The UV-VIS spectra illustrated that iron phthalocyanine was formed during the first solid-phase reaction.The XPS results showed that nitrogen was successfully incorporated into the carbon after the pyrolysis procedure.And the ordered meso-porous structures and high surface area of 548 m2g-1were confirmed by the SEM,TEM and BET analysis results.After the carbon was used to modify the CILE(C-FePhth/CILE),the electrochemical measurements results were conducted.The electrochemical results showed that the C-FePhth/CILE had a rather good electrochemical response upon the luteolin in a pH 3.0 PBS,andshowed a good linear relationship between the measured current values and the concentration of luteolin(2.0×10-81.0×10-44 mol/L),with the detection limit of 6.6×10-99 mol/L(3σ).The evaluation of electrocatalytic performance show that the carbon material obtained has excellent catalytic performance for oxygen reduction reaction(ORR).In an alkaline medium,its catalytic performance for ORR can exceed that of commercial Pt/C catalyst,with its potential 53 mV more positive.Also,the catalyst exhibited excellent methanol tolerance,stability and four-electron process selectivity.5.A kind of biomass-derived porous carbon(BPC)originated from wheat flour was synthesized by alkali activating and carbonizing,which was further employed to obtain Pt-Au-BPC nanocomposite by hydrothermal method.The characteristics and performances of Pt-Au-BPC were checked by SEM,XPS and electrochemical methods,which showed the characteristics including porous structure,large surface area and high conductivity.An electrochemical sensor based on Pt-Au-BPC modified carbon ionic liquid electrode(CILE)was fabricated and applied to the sensitive quercetin determination.Electrochemical behavior of quercetin on Pt-Au-BPC/CILE was studied by cyclic voltammetry and differential pulse voltammetry with the related electrochemical parameters calculated.Under the optimal experimental conditions,the oxidation peak current of quercetin showed good linear relationships with its concentration within 1.5×10-77 to 6.0×10-44 mol/L.The detection limit towards quercetin was confirmed to be 5.0×10-8mol/L(3σ).This fabricated Pt-Au-BPC/CILE was applied to direct detection of quercetin concentration in Ginkgo tablets sample with satisfactory results.