Coaxial Ion Source : pressure dependence of gas flow and field ion emission

We investigated the pressure dependence of gas flow and field ion intensity of a coaxial ion source operating at room temperature over a wide pressure range, testing various gases and ionisation voltages. Flow conductance measurements taking into account the different gases' viscosity and molecular mass consistently exhibit a generic pattern. Three different flow regimes appear with increasing upstream pressure. Since the coaxial ion source supplies the gas locally, very near the apex of the tip where ionisation occurs, large ionisation currents can be obtained without degrading the propagation conditions of the beam. Compared with field ionisation in a partial pressure chamber, using the coaxial ion source increases the ion current a hundredfold for the same residual low pressure. We also show that the gas flow regime does not impact ionisation yield. Although a fuller characterisation remains to be performed, brightness reaches 3 x 10 11 A/m 2 /sr at 12kV extracting voltage. a) https://www.cinam.univ-mrs.fr

Advances in the Use of Microfluidics to Study Crystallization Fundamentals

International audienceThis review compares droplet-based microfluidic systems used to study crystallization fundamentals in chemistry and biology. An original high-throughput droplet-based microfluidic platform is presented. It uses nL droplets, generates a "chemical library" and directly solubilizes powder, thus economizing both material and time. It is compatible with all solvents without the need for surfactant. Its flexibility permits phase diagram determination and crystallization studies (screening and optimizing experiments), and makes it easy to use for non-specialists in microfluidics. Moreover, it allows concentration measurement via UV spectroscopy and solid characterization via XRD analysis

A low-energy electron point-source projection microscope not using a sharp metal tip performs well in long-range imaging

International audienceA low-energy electron point-source projection microscope that uses a metal/insulator structure as source instead of a sharp metal needle is presented. By combining this source with an electron optical lens and a high spatial resolution image detector, performances comparable to those of a normal electron projection microscope are easily accessible and presented here. The accessible electron energy range extends from 100eV to 1000eV. In the example presented here, instead of the usual near-field source-object distance, long-range imaging at a distance of about 600µm is achieved

Coaxial Ion Source : pressure dependence of gas flow and field ion emission

We investigated the pressure dependence of gas flow and field ion intensity of a coaxial ion source operating at room temperature over a wide pressure range, testing various gases and ionisation voltages. Flow conductance measurements taking into account the different gases' viscosity and molecular mass consistently exhibit a generic pattern. Three different flow regimes appear with increasing upstream pressure. Since the coaxial ion source supplies the gas locally, very near the apex of the tip where ionisation occurs, large ionisation currents can be obtained without degrading the propagation conditions of the beam. Compared with field ionisation in a partial pressure chamber, using the coaxial ion source increases the ion current a hundredfold for the same residual low pressure. We also show that the gas flow regime does not impact ionisation yield. Although a fuller characterisation remains to be performed, brightness reaches 3 × 10 11 A/m 2 /sr at 12kV extracting voltage. a) https://www.cinam.univ-mrs.fr

Coaxial Ion Source : pressure dependence of gas flow and field ion emission

We investigated the pressure dependence of gas flow and field ion intensity of a coaxial ion source operating at room temperature over a wide pressure range, testing various gases and ionisation voltages. Flow conductance measurements taking into account the different gases' viscosity and molecular mass consistently exhibit a generic pattern. Three different flow regimes appear with increasing upstream pressure. Since the coaxial ion source supplies the gas locally, very near the apex of the tip where ionisation occurs, large ionisation currents can be obtained without degrading the propagation conditions of the beam. Compared with field ionisation in a partial pressure chamber, using the coaxial ion source increases the ion current a hundredfold for the same residual low pressure. We also show that the gas flow regime does not impact ionisation yield. Although a fuller characterisation remains to be performed, brightness reaches 3 × 10 11 A/m 2 /sr at 12kV extracting voltage. a) https://www.cinam.univ-mrs.fr

Microfluidics set-up rapidly measures solubility directly from powder

International audienceThis communication presents a new microfluidics device for solubility measurement based on the generation of saturated solutions starting from powder and compatible with all solvents and molecules. This device is simple and easily incorporated into any laboratory, even those not specialized in microfluidics. We described the method used to measure solubility, applied here to the pharmaceutical molecules paracetamol and gliclazide in different solvents. The device rapidly measures the solubility of a compound at a variety of temperatures ranging from 20 to 60°C using extremely small quantities (here, only 30mg) of material, with a concentration range from mg/mL to hundreds of mg/mL

Nucleation in Sessile Saline Microdroplets: Induction Time Measurement via Deliquescence-Recrystallization Cycling

Induction time, a measure of how long one will wait for nucleation to occur, is an important parameter in quantifying nucleation kinetics and its underlying mechanisms. Due to the stochastic nature of nucleation, efficient methods for measuring large number of independent induction times are needed to ensure statistical reproducibility. In this work, we present a novel approach for measuring and analyzing induction times in sessile arrays of microdroplets via deliquescence/recrystallization cycling. With the help of a recently developed image analysis protocol, we show that the interfering diffusion-mediated interactions between microdroplets can be eliminated by controlling the relative humidity, thereby ensuring independent nucleation events. Moreover, possible influence of heterogeneities, impurities, and memory effect appear negligible as suggested by our 2-cycle experiment. Further statistical analysis (k-sample Anderson-Darling test) reveals that upon identifying possible outliers, the dimensionless induction times obtained from different datasets (microdroplet lines) obey the same distribution and thus can be pooled together to form a much larger dataset. The pooled dataset showed an excellent fit with the Weibull function, giving a mean supersaturation at nucleation of 1.61 and 1.85 for the 60pL and 4pL microdroplet respectively. This confirms the effect of confinement where smaller systems require higher supersaturations to nucleate. Both the experimental method and the data-treatment procedure presented herein offer promising routes in the study of fundamental aspects of nucleation kinetics, particularly confinement effects, and are adaptable to other salts, pharmaceuticals, or biological crystals of interest

Modular microfluidic platform for solubility measurement, nucleation statistics and polymorph screening of active pharmaceutical ingredients: Irbesartan, Rimonabant, Aripiprazole and Sulfathiazole

Drug efficacy strongly relies on the solid state of the active pharmaceutical ingredient. Classical solid-state screening methods involve different solvent compositions and supersaturations. Moreover, the many repeat experiments needed to address the stochasticity of nucleation make this approach costly. This paper presents a newly developed modular microfluidic platform that provides a universal and flexible plug-and-play tool for crystallisation studies without use of surfactants. By dissolving a powder, our setup generates saturated solutions that can be used for solubility measurements or distributed in microdroplets. Here, we describe solubility measurements performed on different forms, stable and metastable, of pharmaceutical molecules (Irbesartan, Rimonabant and Aripiprazole) in organic and aqueous solvents. In addition, we provide nucleation statistics obtained for Sulfathiazole in water and in acetonitrile. Reporting polymorph screening on Sulfathiazole and statistics for nucleated forms, we find that the cooling rate influences both nucleation and polymorphism results, reflecting the competition between thermodynamics and kinetics. Three unknown forms were discovered, with XRD patterns and Raman spectra that do not match any referenced form. We also demonstrate the limitations of microfluidics for crystallisation by cooling: reducing the crystalliser volume considerably increases nucleation induction time