Determination Of Common Food Additives By High Performance Capillary Electrophoresis

New MEKC methods for the simultaneous analysis of preservatives, synthetic dyes, sweeteners and caffeine contained in different foodstuffs were studied in this paper. The thesis consisted of three sections.In section one, a MEKC method was developed for the simultaneous determination of eleven food additives which are commonly used in beverage, yogurt and candied fruit samples. An uncoated fused-silica capillary with 50 μm i.d. and 70 cm total length(effective length: 60 cm) was used for the separation. The separation buffer consisted of 20 mmol/L sodium tetraborate, 42 mmol/L boric acid(pH 8.83) and 100 mmol/L sodium deoxycholate. The separation voltage was 23 kV and the hydrodynamic injection was at 3448 Pa for 8 s. The detection wavelength was 214 nm. The limits of detection were in the ranges of 0.25 to 2.5 mg/L. While the linear correlation coefficients(r) were above 0.999. The recoveries ranging from 81.6% to 115.0% with RSDs all lower than 5% were obtained, which demonstrated the accuracy of the proposed method. A food analysis performance assessment scheme(FAPAS) proficiency test sample was analyzed. The results showed that the current method with simple sample pretreatment could meet the needs for routine analysis of the eleven additives in beverage, yogurt and candied fruit samples.In section two, a new MEKC method for the determination of nine synthetic dyes in foods in one run was proposed. The nine synthetic dyes(green S, patent blue, indigo carmine, sunset yellow, tartrazine, ponceau, erythrosine, carmoisine and new red) were well separated by using an uncoated fused-silica capillary with 50 μm i.d. and 70 cm total length(effective length: 60 cm). The separation was performed at 25 kV with a buffer comprising of 15 mmol/L sodium tetraborate, 5 mmol/L sodium hydroxide(pH=9.68), 5 mmol/L β-cyclodextrin and 10% EtOH. The limits of detection were in the ranges of 0.25 to 0.5 mg/L. The corrected peak areas(Ac) and the concentrations of the nine synthetic colors showed linear relationships within the ranges of 1.5-200 mg/L, while the linear correlation coefficients(r) were above 0.999. The recoveries ranging from 92.9% to 104.0% with RSDs lower than 5% demonstrated the accuracy of the proposed method. The method has been applied to detect synthetic dyes contained in pocket cocktails, confections, non-alcoholic beverages and ice creams and satisfactory results were obtained.In section three, a new MECK method for the determination of caffeine, theobromine and theophylline in tea in one injection was developed. An uncoated fused-silica capillary with 50 μm i.d. and 60.2 cm total length(effective length: 50 cm) was used during the separation. The separation buffer consisted of 40 mmol/L sodium tetraborate, 150 mmol/L boric acid(pH=8.46), 100 mmol/L sodium dodecyl sulfate, 10g/L PEG20 000 and 5% methanol. The separation was operated at 23 kV and the detected at the wavelength of 214 nm. The calibration curves showed a great linearity within the range of 1.5-100 mg/L, and the correlation coefficients were higher than 0.999. The recovery at three concentration levels ranging from 90.2 to 110.2 %, with the relative standard deviations(RSDs) lower than 5 % indicated the accuracy of the method. The limits of detections for caffeine, theobromine and theophylline were 0.5, 0.2 and 0.5 mg/L, respectively. However, when analysing green tea samples, the content of theophylline was not sufficient enough to be detected. Five green tea samples were analyzed. Theophylline cannot be detected by the current method due to its low content in green tea.Satisfactory results of caffeine and theobrominewere obtained, which demonstrated the accuracy of the current method.