Application of nano-LC - nano-ESI - Orbitrap-MS for trace determination of four priority PFAS in food products considering recently established tolerable weekly intake (TWI) limits

An analytical method was developed and validated for the analysis of four priority perfluoroalkyl substances (PFAS), namely, perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonate (PFOS) in food products using nanoscale liquid chromatography (nano-LC) coupled with nanoscale electrospray ionization (nano-ESI) and Orbitrap mass spectrometry (Orbitrap-MS) detection. The efficiency of two different nano-LC setups for chromatographic separation of selected PFAS was evaluated. The optimal LC separation of analytes was achieved using a reversed phase C18 (RP-C18) nano bore column with an integrated emitter. The effect of matrix concentration factor on signal suppression/enhancement was evaluated for different matrices. The method validation indicated analyte recoveries in the range 83-118% and within-laboratory reproducibility from 7 to 18%, while reanalysis of the materials from proficiency tests (PTs) showed that the accuracy of the obtained concentrations ranged from 85 to 124% of the provided consensus values. The method limits of quantification (m-LOQs) were set as first validation levels ranging from 0.001 to 0.3 ng g^-1 sample depending on the type of the food group. The observed method performance characteristics met the criteria stated in Commission Regulation (EU) 2022/1428, Commission Recommendation (EU) 2022/1431, as well as Guidance Document on Analytical Parameters for the Determination of Per- and Polyfluoroalkyl Substances (PFAS) in Food and Feed with regards to the compliance testing of PFAS maximum levels (MLs) and monitoring purposes. The elaborated method was applied for the analysis of selected priority PFAS in different food groups collected from the Latvian retail market.

New autoimmune diseases after autologous hematopoietic stem cell transplantation for multiple sclerosis

Secondary autoimmune diseases (2ndADs), most frequently autoimmune cytopenias (AICs), were first described after allogeneic hematopoietic stem cell transplantation (HSCT) undertaken for malignant and hematological indications, occurred at a prevalence of ~5-6.5%, and were attributed to allogeneic immune imbalances in the context of graft versus host disease, viral infections, and chronic immunosuppression. Subsequently, 2ndADs were reported to complicate roughly 2-14% of autologous HSCTs performed for an autoimmune disease. Alemtuzumab in the conditioning regimen has been identified as a risk for development of 2ndADs after either allogeneic or autologous HSCT and is consistent with the high rates of 2ndADs when using alemtuzumab as monotherapy. Due to the significant consequences but variable incidence, depending on conditioning regimen, of 2ndADs and similarity in known immune reconstitution kinetics after autologous HSCT for autoimmune diseases and after alemtuzumab monotherapy, we propose that an imbalance between B and T lineage regeneration early after HSCT may underlie the pathogenesis of 2ndADs.

Light-induced gliding of the easy orientation axis of a dye-doped nematic liquid crystal

We studied the effect of light-induced gliding of the easy axis of dye-doped nematic liquid crystal on an aligning polymer surface. The observed drift of the easy axis is over tens of degrees and is caused by light-induced anisotropic adsorption and/or desorption of dye molecules on or from the aligning layer in the presence of light-induced bulk torque. We present a theoretical model that explains the experimental data in terms of the light-induced changes of the adsorbed dye molecules angular distribution due to their exchange with the dye molecules from the liquid crystal bulk.

Evolution of light-induced anchoring in dye-doped nematics: experiment and model

A series of experiments was carried out to describe the evolution of light-induced anchoring in dye-doped nematic liquid crystals (LCs) at irradiation with polarized light. The experiments included cells filled with a pure pentyl-cyanobiphenyl (5CB) and containing a layer of azo dye deposited on an aligning film, as well as cells filled with azo dye doped 5CB, which allowed us to distinguish the role of "surface" and "bulk" dye molecules in the evolution of light-induced anchoring. Modifications of the spectra of spontaneously adsorbed dye molecules under illumination enabled us to assert that light-induced desorption is a mechanism responsible for producing an easy orientation axis in a dark-adsorbed layer. We found that the evolution of light-induced anchoring involves a competition between light-induced desorption and adsorption of the dye molecules on the aligning surface, and the final anchoring is determined by the total light irradiation dose. These data allowed introducing a theoretical model of light-induced anchoring of dye-doped nematic LCs that quantitatively described the experimental results and portrayed the whole evolution of the dye-doped LC cell at irradiation.

Surface reorientation induced by short light pulses in doped liquid crystals

Fast surface reorientation induced by a single 4-ns low-energy laser pulse in dye-doped liquid crystals is reported. The reorientation is due to light-induced modification of the surface anisotropy, which affects the liquid crystal's director through the appearance of a preferred direction on the irradiated surface. The detected signals can be interpreted as being the result of light-induced desorption and adsorption of dye molecules.

Hidden photoalignment of liquid crystals in the isotropic phase

We found the effect of a hidden photoalignment of a dye-doped nematic liquid crystal (LC) on a nonphotosensitive polymer surface after polarized irradiation of the cell in the isotropic phase. We observed that irradiation resulted in a uniform planar orientation of the LC after cooling to the mesophase. The direction of a light-induced easy axis on the polymer can be either parallel or perpendicular to the polarization of the incident light, depending on the light intensity. We attribute this behavior to two mechanisms of photoalignment: light-induced adsorption of dye molecules on the substrate, and anisotropic desorption in a previously adsorbed dye layer. The experimental results on photoalignment of a LC on a thin dye film confirm our model.