Confocal Raman imaging and atomic force microscopy of the surface reaction of NO2 and NaCl(100) under humidity

Polarized confocal Raman imaging combined with non‐contact atomic force microscopy (AFM) was used to study the three‐dimensional evolution of the NaCl(100) surface during its reaction with NO₂ at low pressure as a function of relative humidity (RH) from 0% to nearly 80%. Sea salt particles containing NaCl as the main constituent are believed to be the major source of reactive tropospheric chlorine and nitrate fallouts. At an RH of 0%, the reaction of dry NO₂ generates surface conversion to NaNO₃ monolayer capping the NaCl(100) surface and releases NOCl. The subsequent exposure of this NaNO₃ layer to RH below ∼45% induces the formation of rare NaNO₃ tetrahedral crystals less than 0.5 µm in size. The crystallization occurs through two‐dimensional NO₃⁻ migration under the H₂O monolayer regime. After another subsequent exposure to RH above 45% and below 75%, supermicrometric NaNO₃ rhombohedral plates were obtained under the H₂O multilayer regime. On the other hand, the simultaneous exposure of NaCl(100) to NO₂ and H₂O below ∼45% RH rapidly generates numerous submicrometric NaNO₃ tetrahedra on the NaCl(100) surface. The dramatic increase of NaNO₃ production in the presence of water vapour is explained by the formation of HNO₃ and its easy reaction with the NaCl(100) surface. For RH above 45% and below 75%, the tetrahedra evolve to rhombohedral plates of supermicrometric size. The exposure of NaCl(100) to NO₂/H₂O mixtures under RH above 75% induces the coexistence of both solid‐state NaNO₃ and dissolved NO₃⁻ in droplets. Copyright © 2008 John Wiley & Sons, Ltd.     

Heterogeneous chemistry between PbSO4 and calcite microparticles using Raman microimaging

Currently, the smelting activities of lead and zinc are the loudest sources of local pollution by emission in the troposphere of dust of micrometer size containing PbSO(4). As the particles evolve in the troposphere, their chemical and physical properties - and hence their characteristics such as toxicity - change by accumulation of atmospheric heterogeneous reactions. Calcite (CaCO(3)) represents a large part of the mineral fraction in tropospheric aerosols with aerodynamic diameters less than 10 microm. The calcite particles are expected to react with PbSO(4) particles. In an effort to model the chemical behaviour of PbSO(4) individual particles in the troposphere, we present the in situ Raman imaging results during the course of the reactions in a water droplet of PbSO(4) particles with a calcite microcrystal surface. The computer-microcontrolled XY scanning and Z focusing of confocal Raman imaging combined with multivariate curve resolution (MCR) of Raman images have resolved the severe spectral overlaps of the Raman spectra which are not resolved by the spatial resolution of the instrument ( approximately 1 microm(3)). The results pointed out the identification and the mapping of Pb(3)(CO(3))(2)(OH)(2), PbCO(3) and CaSO(4).2H(2)O (gypsum) on the calcite surface.     

Quantification of sunscreen 2-phenylbenzimidazole-5-sulfonic acid in cosmetic products and water samples by HPTLC/densitometry with fluorescent detection

The water-soluble sunscreen 2-phenylbenzimidazole-5-sulfonic acid (PBS) was quantified in a sun-care product and water samples by thin layer chromatography followed by densitometric scanning in fluorescence mode (cut-off filter 370 nm, wavelength of excitation — 300 nm). Normal phase TLC was performed on silica gel 60 as stationary phase. Mobile phase used was ethyl acetate-ethanol-water 70:35:30 (v/v/v). The limit of detection (LOD) was 0.0004 μg spot-1, and the limit of quantification (LOQ) was — 0.001 μg spot^?1 without any sample pre-concentration.      

Simultaneous NP TLC Analysis of the Sunscreens Diethylamino Hydroxybenzoyl Hexyl Benzoate and Octyl Methoxycinnamate

JPC – Journal of Planar Chromatography – Modern TLC - A simple, rapid, and effective method for TLC separation of two EU-authorized UV filters octyl methoxycinnamate (OMC) and...     

Evaluation of the lipophilicity of selected sunscreens—A chemometric analysis of thin‐layer chromatographic retention data

The lipophilicities of 22 selected sunscreens, preservatives, and vitamins used in topical skin products were measured by thin‐layer chromatography. Lipophilicity was calculated in silico from the sunscreen molecular structures and compared to the experimental octanol/water partition coefficients found in the literature. The retention of the compounds was investigated on an RP‐18 stationary phase with mobile phases consisting of water and one of six organic modifiers (dioxane, tetrahydrofuran, acetone, acetonitrile, methanol, and dimethylformamide) at different concentrations. The theoretical lipophilicities were calculated by several computational algorithms and the results of these calculations were compared using cluster analysis. The results showed that two out of the six investigated organic modifiers (dioxane and acetone) may be used to estimate the octanol/water partition coefficients of highly lipophilic compounds having lipophilicities that cannot be measured directly by the shake‐flask method.     

Simultaneous Multiple-Development HPTLC Quantification of Water- and Oil-Soluble Sunscreens

JPC – Journal of Planar Chromatography – Modern TLC - Acomplex mixture of sunscreens of different lipophilicity was quantified for the first time by thin-layer chromatography (TLC)...     

Particle-particle chemistry between micrometer-sized PbSO4 and CaCO3 particles in turbulent flow initiated by liquid water

A mixture of natural and anthropogenic particles is ubiquitous in the troposphere and exerts an important influence on air quality. This work reports the study of mixing and heterogeneous chemistry of particles of natural-like mineral dust (CaCO(3)) and anthropogenic-like microparticle (PbSO(4)) in turbulent air flow under varying relative humidity. Sparse monolayers of laboratory-generated particles were collected on substrates using impaction. The grain size distribution and chemistry of micrometer-sized particles were determined as CaCO(3)-PbSO(4) internal and external mixtures by Raman imaging, scanning electron microscopy, and time-of-flight static secondary ionization mass spectrometry. The condensation of a thin water layer on mixed aggregates initiates the formation of complex internal mixtures of Pb(3)(CO(3))(2)(OH)(2), PbCO(3), CaSO(4)·2H(2)O, CaCO(3), and PbSO(4) fine particles. These heterogeneous chemistry processes which may occur in ambient air can increase dramatically the amounts of hazardous breathable particles.     

Heterogeneous chemistry between PbSO4 and calcite microparticles using Raman microimaging

Currently, the smelting activities of lead and zinc are the loudest sources of local pollution by emission in the troposphere of dust of micrometer size containing PbSO₄. As the particles evolve in the troposphere, their chemical and physical properties – and hence their characteristics such as toxicity – change by accumulation of atmospheric heterogeneous reactions. Calcite (CaCO₃) represents a large part of the mineral fraction in tropospheric aerosols with aerodynamic diameters less than 10 μm. The calcite particles are expected to react with PbSO₄ particles. In an effort to model the chemical behaviour of PbSO₄ individual particles in the troposphere, we present the in situ Raman imaging results during the course of the reactions in a water droplet of PbSO₄ particles with a calcite microcrystal surface. The computer-microcontrolled XY scanning and Z focusing of confocal Raman imaging combined with multivariate curve resolution (MCR) of Raman images have resolved the severe spectral overlaps of the Raman spectra which are not resolved by the spatial resolution of the instrument (1 μm³). The results pointed out the identification and the mapping of Pb₃(CO₃)₂(OH)₂, PbCO₃ and CaSO₄·2H₂O (gypsum) on the calcite surface.     

Chemistry at level of individual aerosol particle using multivariate curve resolution of confocal Raman image

Airborne particles with aerodynamic diameter in the 10-1 microm range have been collected in an industrial/urban zone by impaction and have been investigated by automated confocal Raman microspectrometry. The computer-microcontrolled XY scanning and Z focusing of Raman images provided many pixel Raman spectra which are characteristics of complex mixture at level of individual particle. The large heterogeneity was not resolved by the spatial resolution of the instrument which is limited by the optical diffraction. The severe spectral overlaps generated by heterogeneity were resolved by multivariate curve resolution (MCR) methods. The purity based method (SIMPLISMAX) was used to resolve both luminescence spectra and pure Raman spectra without prior information. The MCR-alternating least square (ALS) was used as a refined method of both spectra and spectral concentrations. The reconstructing Raman images of the respective spectral contribution supply a versatile potential to characterize the chemistry of atmospheric aerosols at the level of the individual particles.