Preparation And Application Of Methacrylate-based C₁₈ Monolithic Columns For Capillary Ion Chromatography

Capillary ion chromatography (IC) has become an important direction of IC for it has a series of advantages, includes low consumption of mobile phase and sample, easy coupling with mass spectrometry (MS), increase in mass sensitivity, etc.. Between the columns used by capillary IC, monolithic column has a series of advantages: direct synthesis in columns, low flow resistance and no need for packing and frit making. Most of the reports in literatures about monolithic columns used in capillary IC are based on ion-exchange chromatography, and the monolithic columns were used to determine ordinary ions. Sulfate, thiocyanate and thiosulfate are interested anions in clinical assay. However, it is difficult to determine thiocyanate and thiosulfate by ion-exchange chromagraphy for they tend to be polarisable.In this dissertation, the method in reference prepared methacrylate-based C₁₈ monolithic columns was introduced to capillary IC. C₁₈ monolithic columns were constructed by thermally initiated radical polymerization of octadecyl methacrylate (ODMA) and ethylene dimethacrylate (EDMA) in a 530μm i.d. fused silica capillary. Sulfate, thiocyanate and thiosulfate could be well separated from one another on a 40-cm long monolithic column with cetyltrimethylammonium as the ion-interaction reagent and were monitored using direct conductivity detection. Limit of detection (LOD) of three anions were in the range of 0.20-0.93μg mL^-1. The relative standard deviation (RSD) of peak area of three anion (n=5) were in the range of 1.02-4.25%. The calibration graphs of three anions were rectilinear for up to 50μg ml-1. Then this method was applied to determine thiocyanate in human saliva and sulfate in urine. Compared with the ion-pair chromatography methods in reference which were used to determine the two anions, the advantage of the method in this article includes: the preparation of monolithic columns is simple, and the cost is rather low;the consumption of sample and mobile phase is low; the interference of the anions like chloride in the matrix was avoided. The main contents of this dissertation can be divided into four chapters as follows:The first chapter is the introduction. Firstly, the kinds of stationary phase used in IC was simply introduced. One of the stationary phases is monolithic stationary phase which can be divided into polymer-based and silica-based types. The advantages and disadvantages when using the two types of monoliths in IC were compared. Secondly, some theories on Capillary IC and the chromatographic systems on capillary IC were introduced. Lastly, the technical scheme and innovation of this dissertation were introduced respectively.The second chapter mainly discussed the effects of several conditions on the porous properties and the chromatographic performance of the monoliths when preparing the monolithic columns. The conditions include the composition and ratio of the porogens, the ratio of monomer and crosslinking agent, the time and temperature of the polymerization, etc.; Based on reference, theoretical explanation on the results was provided; The reproducibility of the preparation of monolithic columns was investigated, which include the reproducibility of chromatographic performances when used different columns prepared in a same batch, and the reproducibility of chromatographic performances when the same column was used.In the third chapter, the application of capillary C₁₈ polymer based monolithic column to the Capillary IC was investigated. Sulfate, thiocyanate and thiosulfate could be well separated from one another on a 40-cm long monolithic column with cetyltrimethylammonium as the ion-interaction reagent and were monitored using direct conductivity detection. The permeability of the monolithic column and ordinary IC column was compared at the same linear velocity of mobile phase. The effects of several chromatographic conditions on the separation was investigated, including mobile phase and it's concentration, the flow rate, pH of the mobile phase and so on. At last, the limit of detection (LOD), RSD and linearity of the separation of three anions were presented.The fourth chapter was the application of the capillary IC method established to the determination of anion interested in body fluid. Thiocyanate in saliva and sulfate in urine were determined respectively. Sulfate in urine was determined by ordinary IC, then the results was compared with the results obtained by capillary IC.