Determination of the K-value of different types of povidone by microfluidic rheometry and the relationship between K-value and weight-average molecular weight

K-values of 56 batches of 7 types of povidone were measured by microfluidic rheometry and with a Ubbelohde capillary viscometer. The K-values of the two methods were tested by SPSS software and the results showed that there was no significant difference between the two methods (P > 0.05). Taking K-values measured with the Ubbelohde capillary viscometer (K_u) as the abscissa and K-values measured by microfluidic rheometry (K_m) as the ordinate a linear equation was calculated:K_m=0.893 9K_u + 4.617 6, R²=0.986 2, with good linearity, indicating that the microfluidic rheometer method can replace the Ubbelohde capillary viscometer in determining K-values of povidone. The microfluidic rheometer method has the benefits of less sample consumption, faster determination, and is more accurate, and it can be used with high-throughput automatic acquisition, which provides a more convenient method for the determination of K-values of different types of povidone. The weight-average molecular weights (M_w) of each type of povidone were measured by gel permeation chromatography-multi angle laser light scattering (GPC-MALLS), and the relationship between M_w and K_m was lgM_w=-0.000 4 K_m² + 0.072 7 K_m + 2.791, R² =0.990 1. The fitting relationship was good, and M_w could be calculated by K_m by the equation.