Capillary Electrophoresis-Capacitively Coupled Contactless Conductivity Detection For The Analysis Of Carboxyl Compounds

Capillary electrophoresis(CE)is a kind of liquid phase separation technology with capillary tube as the separation channel and high-voltage DC electric field as the driving force.Benefiting from some significant advantages such as various operation modes,high separation efficiency,short analysis time,and low sample and reagent consumption,CE has been developed into an effective and green liquid phase separation technology.Capacitively coupled contactless conductivity detection(C~4D)is a novel detection technique based on the conductance difference between target analytes and background buffer,theoretically responding to all charged substances,thus,C~4D detector can be conveniently used for CE.And nowadays,since it combines the advantages of capillary electrophoresis with high-efficiency separation and the universality of C~4D,capillary electrophoresis with capacitively coupled contactless conductivity detection(CE-C~4D)has shown great potential in a wide range of fields such as pharmaceutical analysis,food analysis and environmental analysis.The laboratory constructed a complete CE-C~4D detection system with the homemade high voltage module and the C~4D detector of eDAQ company.On the basis of these,this paper focused on the analysis of several carboxyl compounds.A method for the analysis of perfluorocarboxylic acids of environmental persistent organic pollutants was developed.At the same time,the derivatization strategy of acrylamide was established,and the corresponding CE-C~4D method was developed for the analysis of acrylamide in food.This paper also developed the CE-C~4D method for the determination of lactic acid and pyruvate and explored the feasibility of this method for lactate dehydrogenase activity evaluation and inhibitor screening.This dissertation can be divided into four chapters:Chapter one:On the basis of the detection technology of capillary electrophoresis,this chapter introduced the principle and the development of the instrument in detail of CE-C~4D.The applications of CE-C~4D technology in biomedical analysis,food analysis and environmental analysis in recent years were also summarized comprehensively.Chapter two:The homemade high voltage module and eDAQ’s C~4D detector were used to assemble the experimental instruments,and a complete CE-C~4D detection system was constructed.On the basis of this,a novel method for the analysis of new persistent organic pollutants perfluorocarboxylic acids(PFCAs)was established.After systematic optimization,the optimal background electrolyte was selected as 20 mM trimethylamine and the separation and detection were completed within 4 minutes.On this basis,β-cyclodextrin-based fluoropolymer(DFB-CDP)was synthesized as solid phase extraction(SPE)material usingβ-cyclodextrin and perfluorobiphenyl,which it was used in SPE for the enrichment of PFCAs in water.Through the comprehensive screening of the the loading pH,flow rate and elution conditions of the sample,the extraction efficiency of the sample was significantly improved and the detection limits were between 0.57 nM and 5.6 nM.The developed method exhibited some merits including small sample matrix interference,high sensitivity and short analysis time,and has been successfully applied to the analysis of PFCAs in environmental water samples.Chapter three:Based on thiol-ene click reaction,a highly efficient derivatization strategy for acrylamide was developed,and a CE-C~4D analysis method for derivative was established.After systematic investigation including catalyst dosage,reaction temperature and time,and cysteine concentration,acrylamide could be efficiently labeled by 2.0 mM cysteine at 70°C for 10 min using 4 mM n-butylamine as catalyst.Application of 10 mM triethylamine as separation buffer,the labeled acrylamide was analyzed within 2.0 min.The method showed good linearity and reproducibility with a detection limit of 0.16μM(11 ng/mL).The method was simple,fast,efficient and economical,assisted further with the QuEChERS sample pretreatment,the developed derivatization strategy and subsequent CE-C~4D method were successfully applied for the determination of acrylamide in potato products.Chapter four:Based on the above CE-C~4D detection system,a method for the analysis of lactic acid and pyruvate was developed.Application of 10 mM triethylamine as separation buffer,the separation and detection of lactic acid and pyruvate were successfully achieved within 5 min,with detection limits of 0.09 and 0.08μM,respectively.On the basis of this,the feasibility of CE-C~4D method for the evaluation of lactate dehydrogenase activity and the screening of inhibitors was studied.After systematic optimization,the peak area of lactic acid and the concentration of lactate dehydrogenase showed a good linear relationship within the range of 0.01 to 10 mU/mL under the optimal incubation conditions,and the detection limit was 0.002 mU/mL.In addition,the inhibition of tartaric acid and ascorbic acid on the activity of lactate dehydrogenase was evaluated by this method.The method had simple operation process and short analysis time.The preliminary analysis results also lay a foundation for the subsequent application of this system in the analysis of lactic acid and pyruvate in biological samples.