CE method for the in-process control of the synthesis of active substances conjugated with gold nanoparticles

Abstract A fast capillary electrophoresis method was developed and validated for the in-process control (IPC) of the synthesis of active substances (APIs) with gold nanoparticles (AuNPs). The capillary electrophoresis method was key to ensure that the reaction step conducted in order to obtain AuNP and API conjugates will produce the expected product without the presence of free APIs, which is a critical parameter determining the quality of the synthetic material. Capillary electrophoresis was performed using uncoated fused-silica capillaries with the effective length of 40 cm, 50 μm i.d. and the background electrolyte consisted of 20 mM borate buffer (pH 8.5) with the application of hydrodynamic injection 50 mbar/5s, voltage 20 kV, temperature of the capillary cassette 25 °C and UV detection at 261 nm for GE, 541 nm for AuNP-GE, 227 nm for PE and 535 nm for AuNP-PE. During validation the specificity, linearity, accuracy, precision, range, and stability of the sample solution were confirmed. The linear regression (R 2  = 0.999) between the corrected peak areas of the analytes and their amount was fulfilled in the range from 2.4 μg/mL to 0.3 mg/mL for genistein and from 4.6 μg/mL to 0.6 mg/mL for pemetrexed. Within this range the method was proved to be accurate (99.0% for genistein and 99.9% for pemetrexed) and precise for both analytes with the intra-day RSD values of 0.77% and 0.97% for the migration time of genistein and pemetrexed, respectively. The inter-day RSD values were 1.90% and 2.27% for the migration time of genistein and pemetrexed, respectively. The LOD and LOQ values for pemetrexed were 1.4 μg/mL and 4.6 μg/mL, respectively, and for genistein 0.72 μg/mL and 2.4 μg/mL, respectively. The results obtained during the validation indicate that the method is sufficient to be applied for the IPC of the synthesis of APIs with gold nanoparticles.