Preparation And Application Of Novel Functionalized Polydopamine-coated Open Tubular Capillary Electrochromatography Column

Objective:(1)In order to solve the issues that conventional preparation methods for polydopamine(PDA)-coated open-tubular capillary electrochromatography(OT-CEC)cannot be directly compatible with the hydrophobic stationary materials,a novel organic amines-assisted method for preparing functional PDA-coated OT-CEC was explored.On this basis,octadecylamine(ODA)modified PDA-coated OT-CEC column was prepared and used for the separation and analysis of a variety of neutral compounds,leading to the improvement of the practicability of PDA-derived materials in CEC.(2)The disadvantages of traditional preparation method of PDA-coated OT-CEC are complicated and time-consuming,poor uniformity and low preparation efficiency,etc.Therefore,the relationship between the deposition rate of PDA coating and reaction temperature as well as reaction time was systematically investigated.An effective and convenient method to achieve the rapid preparation of functional PDA-coated OT-CEC via solvothermal-assisted in situ rapid growth was developed.On the basis,using solvothermal-assisted in-situ coating strategy,PDA/ODA co-deposited OT-CEC column was fabricated quickly and efficiently.It was used for the separation of a variety of neutral and charged compounds.(3)In view of the limitations of chiral selection in electrokinetic chromatography(EKC)with cyclodextrins(CDs)as the separation medium,a new method for the preparation of chiral functional PDA-coated OT-CEC column induced by chiral organic base was developed.Based on this,PDA/quinine(QUI)co-deposition coating OT-CEC column was fabricated,and the chiral selectivity of traditional CD-EKC system was enhanced by the QUI modified PDA coating.It was further used for the enantioseparation of various chiral drugs.Methods:(1)With ODA as an organic amine inducer and hydrophobic modifier,the PDA coating method catalyzed by organic amine and the PDA co-deposition coating strategy were introduced into the preparation of OT-CEC stationary phase.The PDA/ODA co-deposition coating was modified on the capillary inner wall by in-situ one-pot method,and the phase ratio was improved by layer-by-layer self-assembly strategy.The internal surface morphology of the capillary was characterized by field emission scanning electron microscopy(FESEM).Atomic force microscopy(AFM)was used to estimate the increase degree of PDA/ODA aggregates on coating column surface area.The chemical composition of the coating surface was characterized by attenuated total reflection Fourier transform infrared spectroscopy(ATR-FT-IR).The wettability of coating surface was studied by static contact angle measurement.The preparation parameters and chromatographic separation conditions of the coated capillaries were optimized based on the separation performance of alkylbenzenes on the PDA/ODA co-deposited OT-CEC.The main separation mechanism of the coating capillary was also studied.The influence of sample concentration on separation efficiency was investigated,and the mass loadability of coating capillary was tested.The stability and applicability of PDA/ODA co-deposited OT-CEC were verified by the separation of alkylbenzene and progesterone.The chromatographic performance of the PDA/ODA co-deposited capillary was compared with that of the unmodified fused quartz naked column and the conventional PDA coated capillary.(2)In the above studies,the PDA/ODA co-deposited capillary has high phase ratio and CE separation performance.However,the preparation process is complex,tedious and time consuming.Therefore,a high temperature solvothermal assisted PDA rapid co-deposition strategy was further developed to achieve the rapid in-situ co-deposition of PDA and ODA on the capillary inner wall,which significantly improved the preparation efficiency of PDA/ODA co-deposition OT-CEC capillary.The effects of dopamine polymerization time and polymerization temperature on the coating effect were investigated according to the color depth and uniformity of the coating.The inner surface morphology of the capillary and the chemical composition of the coating on the substrate were characterized by FESEM and ATR-FT-IR,and the wettability of the coating surface was studied by static contact angle measurement.The effects of solvothermal reaction temperature,reaction time and mass ratio of PDA/ODA on the formation of hybrid coating and the separation ability of fabricated PDA/ODA co-deposited OT-CEC were investigated.The separation efficiency of PDA/ODA co-deposited OT-CEC was confirmed by using hydrophobic alkylbenzene,halogenated benzene,ionizable aromatic acids and aniline compounds as the analytes and the main separation mechanism was studied.The chromatographic separation performance was compared with those of bare column and conventional PDA coated capillary.The mass loadability of the coated capillary was evaluated by investigating the effect of sample concentration on the separation efficiency.After the stability and reproducibility of the coating column were confirmed,the content of benzoic acid in commercial beverage was determined by using the established electrochromatographic separation method to prove its practical application value.(3)Quinine(QUI)was used as the chiral functional monomer and the oxidative self-polymerization inducer of PDA.QUI and PDA were rapidly in situ co-deposited on the capillary inner wall with the assistance of a solvothermal assisted strategy at high temperature.The inner surface morphology of bare column and fabricated PDA/QUI co-deposition coating capillary were characterized by FESEM.The surfaces chemical composition of the coating was characterized by ATR-FT-IR.Hydroxypropyl-β-cyclodextrin(HP-β-CD)was used as the chiral selector and the racemic chlorpheniramine was used as the model drug for separation.The possibility of synergistic enhancement of the chiral separation efficiency of the CD-EKC system by the PDA/QUI coated column was confirmed.The preparation parameters and chiral separation conditions of the coated capillaries were optimized,and the stability and reproducibility of the PDA/QUI coating capillary were investigated.The fabricated PDA/QUI coated capillary was used for the enantioseparation of a variety of chiral drugs.And the enantioseparation performance was compared with that of bare column,conventional PDA coated capillary and PDA/PEI co-deposition capillary.Results:(1)The surface of the capillary inner wall of PDA/ODA co-deposited coating became very rough with a large number of aggregates by FESEM characterization.Through AFM characterization,it was also found that the surface roughness of PDA/ODA coated quartz wafer was significantly increased compared with that of unmodified quartz plate.The characterization results of ATR-FT-IR on the co-deposition coating showed that it had both the characteristic absorption peaks of benzene ring skeleton,hydroxyl and amino groups belong to PDA and methylene characteristic absorption peaks belong to ODA.Moreover,with the increase of coating times,the corresponding characteristic peak strength also increased.The results of static contact angle measurement show that the hydrophobicity of the substrate surface increased obviously after co-deposition.After three-layer coating,the static contact angle reached 152.2±0.7°,showing super-hydrophobicity.These characterization results all confirm the successful preparation of PDA/ODA co-deposition coating.Under optimized electrophoresis conditions,both alkylbenzene and progesterone could be baseline separated with high efficiency on the PDA/ODA co-deposited OT-CEC capillary.There was a linear relationship between the logarithm of retention factor(log k)of the alkylbenzene and the content of acetonitrile in the running buffer,and the correlation coefficient(R~2)was greater than 0.98,demonstrating the existence of the reversed-phase retention behavior.The mass loadability of the coated capillary is about 3.2 mg/m L,and it has good reproducibility and stability.(2)After the rapid co-deposition of PDA/ODA coating by high temperature solvothermal induction,the surface of capillary inner wall becomes very rough with a large number of aggregated particles by FESEM characterization.The number of aggregates varies obviously under different co-deposition time.The results of ATR-FT-IR characterization of the co-deposited coating showed that it had the characteristic absorption peaks of benzene ring skeleton,hydroxyl and amino groups belong to PDA and methylene characteristic absorption peaks belong to ODA.The results of static contact angle test shown that the hydrophobicity of the substrate surface after PDA/ODA co-deposition was significantly increased compared with that of uncoated quartz.After optimizing the preparation parameters and chromatographic separation conditions of the coating column,the efficient baseline separation of the two kinds of substituted benzenes and the two types of charged compounds was achieved.There was a linear relationship between the logarithm of retention factor(log k)of the five substituted benzene and the content of acetonitrile in the running buffer,and the correlation coefficient(R~2)was greater than 0.98.The mass loadability for methylbenzene was around 2.8 mg/m L.There was a good linear relationship between the mass concentration of benzoic acid and the peak area in the range of0.2 to 4 mg/m L with correlation coefficient(R~2)greater than 0.999.The linear equation of benzoic acid was Y=24.522x+0.8779.The content of benzoic acid in a commercial iced black tea beverage was successfully detected as 0.735 g/kg.(3)FESEM exhibited that the capillary inner wall modified by PDA/QUI co-deposition coating was covered with homogeneous aggregates.ATR-FT-IR characterization results shown that the co-deposition coating was both attributed to the characteristic absorption peaks of PDA and QUI.When 15 m M HP-β-CD was contained in the operating buffer,the separation of the racemic drug chlorpheniramine on the co-deposited capillary could reach 2.05 under the optimized conditions.Compared with uncoated bare column,conventional PDA coated capillary and PDA/PEI co-deposition capillary,the enantioseparation capability of chlorpheniramine,terbutaline,ofloxacin and other racemic drugs by this QUI/PDA co-deposited coated capillary was all significantly enhanced.Moreover,QUI/PDA@capillary could be performed for 80 consecutive injections without significant signs of degradation in the retention time and the enantioseparation performance.Conclusion:(1)A hydrophobic functionalized PDA/ODA co-deposition coating was successfully in situ one-pot modified as a novel OT-CEC stationary phase.The fabricated PDA/ODA co-deposited OT-CEC capillary has excellent separation performance for neutral compounds such as alkylbenzene and progesterone,and the separation follows the reverse phase chromatographic retention mechanism.The PDA co-deposition coating prepared by this strategy can be compatible with hydrophobic molecules and can be used to directly immobilize various hydrophobic functional materials.This strategy provides a new idea for the application of PDA materials in OT-CEC,and is expected to be used in the preparation of other functional PDA coated OT-CEC columns.(2)A new high temperature solvothermal assisted method was developed for the rapid in-situ preparation of functional PDA coatings.The OT-CEC capillary of PDA/ODA co-deposition coating with reverse phase chromatography retention mechanism was efficiently prepared.Under the optimized conditions,alkylbenzene,halogenated benzene,aromatic acid and aniline compounds can be separated efficiently on the PDA/ODA co-deposited OT-CEC column.The practicability of the solvothermal assisted coating strategy in the efficient preparation of high-performance functional PDA modified OT-CEC capillary was proved.In addition,the new electrochromatographic separation and analysis method can be used for the rapid and quantitative determination of aromatic acid content in food,which has a high practical value.(3)A new method for the preparation of chiral functional PDA coating induced by chiral organic base was established.Combined with the high temperature solvothermal assisted strategy,the chiral PDA/QUI co-deposited OT-CEC column was prepared efficiently.Furthermore,the synergistic effect of immobilized QUI and HP-β-CD significantly enhanced the chiral selectivity of traditional CD-EKC system.The CE chiral separation properties of 8 racemic chiral drugs,such as chlorpheniramine,terbutaline and ofloxacin,were significantly improved.Because the PDA chiral functional coating strategy has a certain universality,it is expected to be used to prepare other novel chiral CEC stationary phases,and has a great application prospect in improving the chiral separation performance of CE.