Quantitative analysis of binary mixtures of entecavir using solid-state analytical techniques with chemometric methods

Entecavir (ETV), a guanosine analogue, can be rapidly phosphorylated to the active intracellular triphosphate form that inhibits replication of the hepatitis B virus (HBV). This work aims to develop useful methods to quantify the content of ETV-A in ETV-H and ETV-A binary mixtures. The integral enthalpy value of the phase transformation in the DSC thermogram was selected to quantify the content of ETV-A in binary mixture. Different ranges (full spectrum and partial spectrum) of the PXRD and ATR-FTIR data versus ETV-A content were used to develop partial least squares (PLS) calibration curves with different pre-processing algorithms including multiplicative scatter correction (MSC), standard normal variate (SNV), wavelet transform (WT) or their combinations. The standard curve obtained for the DSC technique is Y = 100.455 + 7.255X, R2 = 0.997, in the ETV-A contents range of 0–100% w/w% in binary mixtures. Limit of detection (LOD) of ETV-A was 0.909% and limit of quantitation (LOQ) is 2.755%. The best correction models for PXRD and ATR-FTIR techniques, in the ETV-A contents range of 0–100% w/w% in binary mixtures, were Y = 0.346 + 0.999X, R2 = 0.999 in the 2θ range of 4-6° with 14-34° and Y = 0.767 + 0.991X, R2 = 0.991 in the range of 3500–2500 cm−1 with 2000–400 cm−1 pretreated by MSC + WT, respectively. Limit of detection (LOD) of ETV-A was 1.394% and limit of quantitation (LOQ) was 4.224% for PXRD technique. LOD and LOQ for ATR-FTIR technique were 9.124% and 27.648%. The results show that DSC, PXRD and ATR-FTIR techniques are precise and accurate, and could be used for the measurement of ETV-A content in the binary mixtures.