Development and validation of a stability-indicating ultra-high-performance liquid chromatography method for the estimation of ibrutinib and trace-level quantification of related substances using quality-by-design approach.

A new ultra-high-performance liquid chromatography method was developed using quality-by-design principles for quantifying trace-level impurities of ibrutinib. The method utilized an ACQUITY UPLC BEH C18 column with a mobile phase consisting of equal parts of 0.02 M formic acid in water and 0.

Identification of extractables by liquid chromatography-high resolution mass spectrometry: A case study to understand the extraction profile of different disposable syringes.

The current study was undertaken to evaluate clinical-grade disposable syringes of various brands based on the identification of an extraneous impurity leaching out from the rubber gasket of the syringe during sample preparation for liquid chromatography method development. The syringes were evaluated using aqueous and organic solvents and their mixtures to understand susceptibility towards extractables. It was observed that the extraction propensity of different brands of syringes was varying in terms of number and levels of extractables.

Interfacial segregation in polymer blends driven by acid-base interactions.

Infrared-visible sum frequency generation spectroscopy (SFG) was used to measure the interfacial concentrations of poly(methyl methacrylate) (PMMA)/polystyrene (PS) blends next to a sapphire substrate. The acid-base interactions of carbonyl groups of PMMA with the hydroxyl groups on the sapphire drive the interfacial segregation of PMMA next to the sapphire substrate. Using the shift of sapphire surface OH peaks, we have determined the difference in interfacial energy between the PMMA/sapphire and the PS/sapphire to be ~44-45 mJ/m(2).

Direct measurement of acid-base interaction energy at solid interfaces.

We have studied acid-base interactions at solid-liquid and solid-solid interfaces using interface-sensitive sum frequency generation (SFG) spectroscopy. The shift of the sapphire hydroxyl peak in contact with several polar and nonpolar liquids and polymers was used to determine the interaction energy. The trend in the interaction energies cannot be explained by measuring only water contact angles.

Effect of surface freezing on meniscus relaxation in side chain comb polymers.

We have observed a sharp slowing down of the relaxation of the liquid meniscus for poly(n-alkyl acrylate) at temperatures where there are no abrupt changes in bulk viscosity or surface tension. This slowing down is due to the formation of a surface-ordered monolayer above the bulk melting temperatures. X-ray photon correlation spectroscopy measurements reveal that the surface capillary fluctuations are also significantly slower due to the formation of the ordered monolayer for film thicknesses comparable to that of the precursor films.

Partial crystallinity in alkyl side chain polymers dictates surface freezing.

We have studied the structure of a novel crystalline surface monolayer on top of a disordered melt of the same material [poly(n-alkyl acrylate)s] using grazing incidence x-ray diffraction. The grazing incidence x-ray diffraction, surface tension, and bulk latent heat results show that side chains crystallize except the nine methylene units of the alkyl side chains closest to the polymer backbone. The partial crystallinity along with a thicker surface layer, due to the additional length of the linker group, explains why the difference between the surface order-to-disorder transition temperature and bulk melting temperature increases with a decrease in the length of the alkyl side chain.

Dynamic interfacial tension at the oil/surfactant-water interface.

We have used dynamic interfacial tension measurements to understand the structure of the ordered monolayer at the hexadecane/water interface induced by the presence of surfactant molecules. No abrupt changes in the interfacial tension (gamma) are observed during the expansion and contraction cycle below the interfacial ordering temperature (Ti) as observed for alkanes in contact with air. The lack of an abrupt change in gamma and the magnitude of this change during the expansion process indicate that the ordered phase may not be crystalline.

Rupture of a two-dimensional alkane crystal.

We have studied the breaking of a two-dimensional alkane crystal above the disordered melt using an oscillating bubble rheometer. Surface tension changes abruptly during the expansion and contraction cycle. We postulate that this is due to rupture of the 2D crystal at grain boundaries.