Effect of apolar phase dielectric constant on interfacial properties of β-lactoglobulin (dielectric constant and interfacial properties of β-lactoglobulin)

Lipemia in the Plasma Sample Affects Fentanyl Measurements by Means of HPLC-MS2 after Liquid-Liquid Extraction

Examination of fentanyl levels is frequently performed in certain scientific evaluations and forensic toxicology. It often involves the collection of very variable blood samples, including lipemic plasma or serum. To date, many works have reported the methods for fentanyl detection, but none of them have provided information about the impact on the assay performance caused by an excessive amount of lipids. This aspect may be, however, very important for highly lipophilic drugs like fentanyl. To address this issue, we developed the liquid chromatography method with mass spectrometry detection and utilized it to investigate the impact of lipids presence in rabbit plasma on the analytical method performance and validation. The validation procedure, conducted for normal plasma and lipemic plasma separately, resulted in good selectivity, sensitivity and linearity. The limits of detection and quantification were comparable between the two matrices, being slightly lower in normal plasma (0.005 and 0.015 µg/L) than in lipemic plasma (0.008 and 0.020 µg/L). Liquid–liquid extraction provided a low matrix effect regardless of the lipid levels in the samples (<10%), but pronounced differences were found in the recovery and accuracy. In the normal plasma, this parameter was stable and high (around 100%), but in the lipemic matrix, much more variable and less efficient results were obtained. Nevertheless, this difference had no impact on repeatability and reproducibility. In the present work, we provided reliable, convenient and sensitive method for fentanyl detection in the normal and lipemic rabbit plasma. However, construction of two separate validation curves was necessary to provide adequate results since the liquid-liquid extraction was utilized. Therefore, special attention should be paid during fentanyl quantification that involves lipemic plasma samples purified by this technique.

Effects of aqueous phase composition upon protein destabilization at water/organic solvent interface

The objective of this study was to evaluate the effects of an aqueous phase composition upon the destabilization of lactoglobulin toward emulsification. Eight different buffers were used to make aqueous lactoglobulin solutions at pH 5.6-9. Each buffer concentration varied from 20 to 60, 100, and 150 mM. After emulsification of the aqueous solutions in methylene chloride, the aqueous contents of lactoglobulin were determined by a native SEC-HPLC assay. The properties of lactoglobulin precipitates detected at the water/methylene chloride interface were assessed by SDS-PAGE experiments. Dynamic interfacial tension was also monitored to examine the interfacial adsorption of lactoglobulin. When dissolved in plain water, only 41.1+/-1.4% of lactoglobulin was recovered after emulsification. The remaining lactoglobulin became aggregated at the interface. A series of SDS-PAGE experiments demonstrated that its aggregation was driven by intermolecular covalent linkages and hydrophobic interactions. Interestingly, both the buffer type and its concentration considerably influenced the degree of lactoglobulin recovery. For instance, at 150 mM buffer concentrations, percent recovery of lactoglobulin was as low as 27.3+/-1.7%. In contrast, the degree of its recovery increased up to 89.4+/-3.9% at a 20 mM buffer concentration. The dynamic interfacial tension study substantiated that at an optimal concentration buffer species helped lactoglobulin molecules to better withstand interfacial destabilization. Therefore, choosing a suitable buffer and its concentration should deserve special attention, since they could affect the interfacial stability of a protein of interest during emulsification.