Evaluation of efficiency and trapping capacity of restricted access media trap columns for the online trapping of small molecules

Poly-ε-caprolactone Nanofibrous Polymers: A Simple Alternative to Restricted Access Media for Extraction of Small Molecules from Biological Matrixes

Poly-ε-caprolactone nanofibrous polymer has been used as an alternative to restricted access media for extraction of protein-containing biological samples and direct transfer in the chromatographic system. Three commercial cartridges differing in length and internal diameter have been manually packed with the composite material prepared from poly-ε-caprolactone nanofibers coated on poly-ε-caprolactone microfibrous scaffold and connected to the column-switching chromatographic system. Bovine milk and human serum (25 μL) spiked with a mixture of methyl-, ethyl-, propyl-, and butylparaben in a concentration range of 1-100 μg mL^-1 were online extracted using the cartridge-containing fibers. Then, 5 and 20% (v/v) aqueous methanol was applied as the washing mobile phase. While the ballast protein macromolecules were quantitatively eluted from the nano/microfibrous composite sorbent, the parabens were retained. After the mobile phase was switched to a stronger one, these compounds were then eluted from the extraction sorbent, directed in the analytical column, and finally separated. An extraction efficiency of 86-101% for all parabens achieved using the optimum-sized cartridge and a repeatability of the extraction procedure of 0.06-1.95% RSD were obtained.

An integrated multipath liquid chromatography-mass spectrometry system for the simultaneous preparation, separation, and detection of proteins and small molecules

A multipath liquid chromatography with mass spectrometry instrument was constructed with the help of restricted access media to online segregate small and large molecules. This liquid chromatography system was custom built with five pumps and three two-position six-port valves to control the flow in a multipath system for the simultaneous analysis of small molecules and proteins. On separate chromatographic channels, small molecules trapped and proteins excluded from the online restricted access media were analyzed downstream using high-efficiency columns and a triple quadrupole mass spectrometer. A model sample, which included five proteins and 22 small molecules with different physicochemical properties, was used to evaluate the system. Following injection, the complete multipath separation and detection was performed in 22 min. Protein exclusion by the restricted access media was not quantitative. Four commercial trap columns were evaluated for their exclusion efficiency toward the proteins. Exclusion efficiency varied from <50% to only a maximum of 75% exclusion across the trap columns tested. An attempt was made to optimize the exclusion efficiency using different flow rates, flow rate gradients, and different additives both in the sample and the mobile phases. Protein exclusion was still erratic and generally nonquantitative.

Online extraction of antihypertensive drugs and their metabolites from untreated human serum samples using restricted access carbon nanotubes in a column switching liquid chromatography system

A novel analytical method was developed to determine 5 antihypertensive drugs of different pharmacological classes (angiotensin-converting enzyme inhibitors, calcium channel blockers, α-2 adrenergic receptor agonists, angiotensin II receptor blockers, and aldosterone receptor antagonists) and some of their metabolites in human serum. The untreated samples were directly analyzed in a column switching system using an extraction column packed with restricted access carbon nanotubes (RACNTs) in an ultra-high performance liquid chromatography coupled to a mass spectrometer (UHPLC-MS/MS). The RACNTs column was able to exclude approximately 100% of proteins from the samples in 2.0min, maintaining the same performance for about 300 analytical cycles. The method was validated in accordance with Food and Drug Administration (FDA) guidelines, being linear for all the determined analytes in their respective analytical ranges (coefficients of determination higher than 0.99) with limits of detection (LODs) and quantification (LOQs) ranging from 0.09 to 10.85μgL^-1 and from 0.30 to 36.17μgL^-1, respectively. High recovery values (88-112%) were obtained as well as suitable results for inter and intra-assay accuracy and precision. The method provided an analytical frequency of 5 samples per hour, including the sample preparation and separation/detection steps. The validated method was successfully used to analyze human serum samples of patients undergoing treatment with antihypertensive drugs, being useful for pharmacometabolomic, pharmacogenomic, and pharmacokinetic studies.

Targeted quantification of lipid mediators in skeletal muscles using restricted access media-based trap-and-elute liquid chromatography-mass spectrometry

Lipid mediators (LMs) are a class of bioactive metabolites of the essential polyunsaturated fatty acids (PUFA), which are involved in many physiological processes. Their quantification in biological samples is critical for understanding their functions in lifestyle and chronic diseases, such as diabetes, as well allergies, cancers, and in aging processes. We developed a rapid, and sensitive LC-MS/MS method to quantify the concentrations of 14 lipid mediators of interest in mouse skeletal muscle tissue without time-consuming liquid-liquid or solid-phase extractions. A restricted-access media (RAM) based trap was used prior to LC-MS as cleanup process to prevent the analytical column from clogging and deterioration. The system enabled automatic removal of residual proteins and other biological interferences presented in the tissue extracts; the target analytes were retained in the trap and then eluted to an analytical column for separation. Matrix evaluation tests demonstrated that the use of the combined RAM trap and chromatographic separation efficiently eliminated the biological or chemical matrix interferences typically encountered in bioanalytical analysis. Using 14 LM standards and 12 corresponding deuterated compounds as internal standards, the five-point calibration curves, established over the concentration range of 0.031-320 ng mL^-1, demonstrated good linearity of r² > 0.9903 (0.9903-0.9983). The lower detection limits obtained were 0.016, 0.031, 0.062, and 0.31 ng mL^-1 (0.5, 1, 2, and 10 pg on column), respectively, depending on the specific compounds. Good accuracy (87.1-114.5%) and precision (<13.4%) of the method were observed for low, medium, and high concentration quality control samples. The method was applied to measure the amount of 14 target LMs in mouse skeletal muscle tissues. All 14 analytes in this study were successfully detected and quantified in the gastrocnemius muscle samples, which provided crucial information for both age and gender-related aspects of LMs signaling in skeletal muscles previously unknown. This method could be applied to advance the understanding of skeletal muscle pathophysiology to study the role of LMs in health and disease. Furthermore, we will expand the application of this methodology to humans and other tissues/matrices in the near future.