Extractability-mediated stability bias and hematocrit impact: High extraction recovery is critical to feasibility of volumetric adsorptive microsampling (VAMS) in regulated bioanalysis.

Volumetric absorptive microsampling (VAMS), a new microsampling technique, was evaluated for its potential in supporting regulated bioanalysis. Our initial assessment with MK-0518 (raltegravir) using a direct extraction method resulted in 45-52% extraction recovery, significant hematocrit (Ht) related bias, and more importantly, unacceptable stability (>15% bias from nominal concentration) after 7-day storage. Our investigation suggested that the observed biases were not due to VAMS absorption, sampling techniques, lot-to-lot variability, matrix effect, and/or chemical stability of the compound, but rather the low extraction recovery. An effort to improve assay recovery led to a modified liquid-liquid extraction (LLE) method that demonstrated more consistent performance, minimal Ht impact (Ht ranged from 20 to 65%), and acceptable sample stability. The same strategy was successfully applied to another more hydrophilic model compound, MK-0431 (sitagliptin). These results suggest that the previously observed Ht effect and "instability" were in fact due to inconsistent extractability, and optimizing the extraction recovery to greater than 80% was critical to ensure VAMS performance. We recommend adding Ht-independent recovery as part of feasibility assessment to de-risk the long-term extractability-mediated stability bias before implementing VAMS in regulated bioanalysis.

Developing imprinted polymer nanoparticles for the selective separation of antidiabetic drugs.

In this study, new molecularly imprinted polymer (MIP) nanoparticles are designed for selective recognition of different drugs used for the treatment of type 2 diabetes mellitus, i.e. sitagliptin (SG) and metformin (MF). The SG- and MF-imprinted polymer nanoparticles are synthesized by free-radical initiated polymerization of the functional monomers: methacrylic acid and methyl methacrylate; and the crosslinker: ethylene glycol dimethacrylate. The surface morphology of resultant MIP nanoparticles is studied by atomic force microscopy. Fourier transform infrared spectra of MIP nanoparticles suggest the presence of reversible, non-covalent interactions between the template and the polymer. The effect of pH on the rebinding of antidiabetic drugs with SG- and MF-imprinted polymers is investigated to determine the optimal experimental conditions. The molecular recognition characteristics of SG- and MF-imprinted polymers for the respective drug targets are determined at low concentrations of SG (50-150 ppm) and MF (5-100 ppm). In both cases, the MIP nanoparticles exhibit higher binding response compared to non-imprinted polymers. Furthermore, the MIPs demonstrate high selectivity with four fold higher responses toward imprinted drugs targets, respectively. Recycled MIP nanoparticles retain 90% of their drug-binding efficiency, which makes them suitable for successive analyses with significantly preserved recognition features.