Multivariate optimization of large-volume sample stacking with polarity switching by capillary electrophoresis for determination of gold nanoparticle size

Gold nanoparticles (AuNPs) are widely studied and applied due to their unique optical characteristics, such as surface plasmon resonance and extinction coefficient. In this study, large sample stacking combined with polarity switching (LVSS-PS) by capillary electrophoresis was established to determine AuNP mixtures with different particle sizes simultaneously. The multivariate experimental design containing fractional factorial design (fFD) and central composite design (CCD) was combined with LVSS-PS to estimate the optimal condition. The influence of factors on the response was evaluated by the use of the chromatography resolution statistic function to simultaneously investigate the resolution and separation under twenty-eight sets of capillary electrophoresis conditions. The results showed that the optimal condition of the separation buffer was 100 mM CAPS (pH 9.5) with 20 mM SDBS and 35 mM SDS. The separation temperature was set at 20 °C. Under this condition, four different diameters of AuNPs (5, 20, 50, and 80 nm) were successfully separated in the same run. The linear relationship between the electrophoretic mobility of AuNPs and their diameters was established, and the correlation coefficient was 0.99. Sodium citrate and gallic acid (GA) were capping agents to synthesize AuNPs. The established method was applied to determine the size of gold nanoparticles synthesized by sodium citrate and gallic acid as capping agents, respectively. The diameters of the AuNPs obtained by LVSS-PS are consistent with transmission electron microscopy.