Miniaturized dynamic liquid-liquid extraction of organophosphate triesters from blood plasma using the hollow fibre-based XT-tube extractor

A miniaturized liquid–liquid extractor for bioanalytical sample preparation is described. The extractor consists of a polypropylene hollow fibre mounted inside polytetrafluoroethylene (PTFE) tubing by means of a cross (X) connector and a tee (T) connector. All parts are commercially available, inexpensive, and easily assembled. The aqueous sample, injected into a carrier flow, is pumped along the outside of the fibre and the organic phase, which also wets the pores of the hollow fibre wall, is pumped inside. Eight organophosphate triester (OPE) plasticisers/flame retardants were extracted from 50 µL spiked blood plasma that had been mixed with 50 µL formic acid to denature plasma proteins. The organic phase was a mixture of hexane and methyl tert-butyl ether (MTBE). A high concentration of formic acid in the sample and of MTBE in the organic phase had positive effects on the recovery of some OPE. When investigating the recovery as a function of extraction time it was found that the extraction reached a maximum after 10 min, at a flow-rate of 15 µL min^–1. Recoveries varied between 40 and 80% with RSD around 4% for most compounds. The whole 150-µL extract was injected into a GC–MS system equipped with a programmed-temperature vaporization (PTV) injector. With the MS in selected-ion monitoring (SIM) mode, the LOD for triphenyl phosphate and 2-ethylhexyl diphenyl phosphate were 0.3 and 0.2 ng mL^–1, respectively. More than 40 plasma extractions were performed with the same fibre without any detectable change in extraction efficiency.     

Silicate-Phenolic Networks: Coordination-Mediated Deposition of Bioinspired Tannic Acid Coatings

Surface modification with polyphenolic molecules has been pursued in biomedical materials owing to their antioxidant, anti-inflammatory, and antimicrobial characteristics. Recently, the use of silicic acid (Si_aq) as a mediator for efficient surface deposition of tannic acid (TA) was reported, but the postulated Si-TA polymeric networks were not characterized. Herein, we present unambiguous evidence for silicate-TA networks that involve Si−O−C motifs by using solid-state NMR spectroscopy, further supported by XPS and ToF-SIMS. By using QCM-D we demonstrate the advantages of Si_aq, compared to using transition-metal ions, to improve the coating efficiency under mildly acidic conditions. The presented homogenous coating buildup and validated applicability in inorganic buffers broadens the use of TA for surface modifications in technological and biomedical applications.     

Nonlinear Isolator Dynamics at Finite Deformations: An Effective Hyperelastic,Fractional Derivative,Generalized Friction Model

In presenting a nonlinear dynamic model of a rubber vibrationisolator, the quasistatic and dynamic motion influences on theforce response are investigated within the time and frequencydomain. It is found that the dynamic stiffness at the frequency ofa harmonic displacement excitation, superimposed upon the longterm isolator response, is strongly dependent on staticprecompression, dynamic amplitude and frequency. The problems ofsimultaneously modelling the elastic, viscoelastic and frictionforces are removed by additively splitting them, modelling theelastic force response by a nonlinear, shape factor basedapproach, displaying results that agree with those of aneo-Hookean hyperelastic isolator at a long term precompression.The viscoelastic force is modeled by a fractional derivativeelement, while the friction force governs from a generalizedfriction element displaying a smoothed Coulomb force. A harmonicdisplacement excitation is shown to result in a force responsecontaining the excitation frequency and its every otherhigher-order harmonic, while using a linearized elastic forceresponse model, whereas all higher-order harmonics are present forthe fully nonlinear case. It is furthermore found that the dynamicstiffness magnitude increases with static precompression andfrequency, while decreasing with dynamic excitationamplitude – eventually increasing at the highest amplitudes due tononlinear elastic effects – with its loss angle displaying amaximum at an intermediate amplitude. Finally, the dynamicstiffness at a static precompression, using a linearized elasticforce response model, is shown to agree with the fully nonlinearmodel except at the highest dynamic amplitudes.     

A component tracking algorithm for accelerated and improved liquid chromatography-mass spectrometry method development

A method for tracking of sample components during liquid chromatography-mass spectrometry (LC-MS) method development has been proposed. The method manages to, fully automatically and without user intervention, find the chromatographic peaks in the data sets, discriminate them to sample components and track them when the separation conditions have been changed. The algorithm utilises the resolution obtained from all considered data sets and has the ability to discriminate the non informative parts. The technique has a great sensitivity even in cases where a majority of the tracked components cannot easily be spotted by means of traditional total ion chromatogram (TIC) or base peak chromatogram (BPC) representations. The method was tested on an experimental sample using six different columns and an average of 79% of the suggested sample components could be successfully tracked at a minimum area of 0.05% of the main component in the sample. 66 components with 79-92% of the total suggested component area were able to be tracked between all data sets. The method could be used to rapidly investigate selectivity during different types of separation conditions.     

Combining column generation and constraint programming to solve the tail assignment problem

Within the area of short term airline operational planning, Tail Assignment is the problem of assigning flight legs to individual identified aircraft while satisfying all operational constraints, and optimizing some objective function. In this article, we propose that Tail Assignment should be solved as part of both the short and the long term airline planning. We further present a hybrid column generation and constraint programming solution approach. This approach can be used to quickly produce solutions for operations management, and also to produce close-to-optimal solutions for long and mid term planning scenarios. We present computational results which illustrate the practical usefulness of the approach.     

Photospin-orbit coupling in photonic structures

We show that the inclusion of nonlocality in the constitutive relations in photonic structures has important repercussions in their eigenmode configuration and distribution. In the case of optical activity, the primary manifestation of nonlocality, these features are traced to a photospin-orbit interaction analogous to the electron spin-orbit interaction in asymmetric semiconducting compounds; its impact can be assimilated to that of a magnetic field whose magnitude and direction follow that of the photon quasimomentum, with implications in photospin transport and photospintronics.     

Ice nucleation and phase behavior on oligo(ethylene glycol) and hydroxyl self-assembled monolayers: simulations and experiments

The nucleation and phase behavior of ultrathin D2O-ice overlayers have been studied on oligo(ethylene glycol) (OEG)-terminated and hydroxyl self-assembled monolayers (SAMs) at low temperatures in ultrahigh vacuum. Infrared reflection-absorption spectroscopy (IRAS) is used to characterize the ice overlayers, the SAMs, and the interactions occurring between the ice and the SAM surfaces. Spectral simulations, based on optical models in conjunction with Maxwell Garnett effective medium theory, point out the importance of including voids in the modeling of the ice structures, with void fractions reaching 60% in some overlayers. The kinetics of the phase transition from amorphous-like to crystalline-like ice upon isothermal annealing at 140 K is found to depend on the conformational state of the supporting OEG SAM surface. The rate is fast on the helical OEG SAMs and slow on the corresponding all-trans SAMs. This difference in kinetics is most likely due to a pronounced D2O interpenetration and binding to the all-trans segments of the ethylene glycol portion of the SAM. No such penetration and binding was observed on the helical OEG SAM.     

Speeding up MCMC by Delayed Acceptance and Data Subsampling

The complexity of the Metropolis–Hastings (MH) algorithm arises from the requirement of a likelihood evaluation for the full dataset in each iteration. One solution has been proposed to speed up the algorithm by a delayed acceptance approach where the acceptance decision proceeds in two stages. In the first stage, an estimate of the likelihood based on a random subsample determines if it is likely that the draw will be accepted and, if so, the second stage uses the full data likelihood to decide upon final acceptance. Evaluating the full data likelihood is thus avoided for draws that are unlikely to be accepted. We propose a more precise likelihood estimator that incorporates auxiliary information about the full data likelihood while only operating on a sparse set of the data. We prove that the resulting delayed acceptance MH is more efficient. The caveat of this approach is that the full dataset needs to be evaluated in the second stage. We therefore propose to substitute this evaluation by an estimate and construct a state-dependent approximation thereof to use in the first stage. This results in an algorithm that (i) can use a smaller subsample m by leveraging on recent advances in Pseudo-Marginal MH (PMMH) and (ii) is provably within O(m^{? 2}) of the true posterior.