A Fluorescent Probe for Diacetyl Detection

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl

Thermodynamics of the Formaldehyde−Water and Formaldehyde−Ice Systems for Atmospheric Applications

International audienceFormaldehyde (HCHO) is a species involved in numerous key atmospheric chemistry processes that can significantly impact the oxidative capacity of the atmosphere. Since gaseous HCHO is soluble in water, the water droplets of clouds and the ice crystals of snow exchange HCHO with the gas phase and the partitioning of HCHO between the air, water, and ice phases must be known to understand its chemistry. This study proposes thermodynamic formulations for the partitioning of HCHO between the gas phase and the ice and liquid water phases. A reanalysis of existing data on the vapor−liquid equilibrium has shown the inadequacy of the Henry's law formulation, and we instead propose the following equation to predict the mole fraction of HCHO in liquid water at equilibrium, XHCHO,liq, as a function of the partial pressure PHCHO (Pa) and temperature T (K): XHCHO,liq = 1.700 × 10−15 e(8014/T)(PHCHO)1.105. Given the paucity of data on the gas−ice equilibrium, the solubility of HCHO and the diffusion coefficient (DHCHO) in ice were measured by exposing large single ice crystals to low PHCHO. Our recommended value for DHCHO over the temperature range 243−266 K is DHCHO = 6 × 10−12 cm2 s−1. The solubility of HCHO in ice follows the relationship XHCHO,ice = 9.898 × 10−13 e(4072/T)(PHCHO)0.803. Extrapolation of these data yields the PHCHO versus 1/T phase diagram for the H2O−HCHO system. The comparison of our results to existing data on the partitioning of HCHO between the snow and the atmosphere in the high arctic highlights the interplay between thermodynamic equilibrium and kinetics processes in natural systems

Acetaldehyde in the Alaskan subarctic snowpack

International audienceAcetaldehyde is a reactive intermediate in hydrocarbon oxidation. It is both emitted and taken up by snowpacks and photochemical and physical processes are probably involved. Understanding the reactivity of acetaldehyde in snow and its processes of physical and chemical exchanges requires the knowledge of its incorporation mechanism in snow crystals. We have performed a season-long study of the evolution of acetaldehyde concentrations in the subarctic snowpack near Fairbanks (65° N), central Alaska, which is subjected to a vigorous metamorphism due to persistent elevated temperature gradients in the snowpack, between 20 and 200° C m−1. The snowpack therefore almost entirely transforms into depth hoar. We have also analyzed acetaldehyde in a manipulated snowpack where temperature gradients were suppressed. Snow crystals there transformed much more slowly and their original shapes remained recognizable for months. The specific surface area of snow layers in both types of snowpacks was also measured. We deduce that acetaldehyde is not adsorbed onto the surface of snow crystals and that most of the acetaldehyde is probably not dissolved in the ice lattice of the snow crystals. We propose that most of the acetaldehyde measured is either trapped or dissolved within organic aerosol particles trapped in snow, or that acetaldehyde is formed by the hydrolysis of organic precursors contained in organic aerosols trapped in the snow, when the snow is melted for analysis. These precursors are probably aldehyde polymers formed within the aerosol particles by acid catalysis, but might also be biological molecules. In a laboratory experiment, acetaldehyde-di-n-hexyl acetal, representing a potential acetaldehyde precursor, was subjected to our analytical procedure and reacted to form acetaldehyde. This confirms our suggestion that acetaldehyde detected in snow could be produced during the melting of snow for analysis

Application of a data-processing model to determine the optimal sampling conditions for liquid phase trapping of atmospheric carbonyl compounds

International audienceThe reactivity of two fluorescent derivatization reagents, 2-diphenyl-1,3-indandione-1-hydrazone (DIH) and 2-aminooxy-N-[3-(5-dimethylamino-naphtalene-1-sulfonamino)-propyl]-acetamide (dansylacetamidooxyamine, DNSAOA), was studied towards selected atmospheric carbonyl compounds. The results were compared to those obtained using the 2,4-dinitrophenylhydrazine (2,4-DNPH) UV–vis reagent, a standard well-established technique used to detect atmospheric carbonyl compounds. The experimental rate constant were integrated into a data-processing model developed in the laboratory to simulate the trapping efficiencies of a mist chamber device as a function of temperature, reagent and solvent type among others. The results showed that in an aqueous solution, DNSAOA exhibits a higher reactivity towards carbonyl compounds without the addition of an acidic catalyst than 2,4-DNPH. It was observed that DNSAOA can trap efficiently water-soluble gaseous compounds (for example formaldehyde). However, because of a high initial contamination of the reagent caused by the synthesis procedure used in this work, DNSAOA cannot be used in high concentrations. As a result, very low trapping efficiencies of less reactive water-insoluble gaseous compounds (acetone) using DNSAOA are observed. However, the use of an organic solvent such as acetonitrile improved the trapping efficiencies of the carbonyl compounds. In this case, using DIH as the derivatization reagent (DNSAOA is not soluble in acetonitrile), trapping efficiencies greater than 95% were obtained, similar to 2,4-DNPH. Moreover, fluorescence associated with DIH derivatives (detection limits 3.33 × 10−8 M and 1.72 × 10−8 M for formaldehyde and acetone, respectively) is further advantage of this method for the determination of carbonyl compounds in complex matrix compared to the classical UV–vis detection method (detection limits 3.20 × 10−8 M and 2.9 × 10−8 M for formaldehyde and acetone, respectively)

Sensitive determination of glyoxal, methylglyoxal and hydroxyacetaldehyde in environmental water samples by using dansylacetamidooxyamine derivatization and liquid chromatography/fluorescence

International audienceIn this study we improved the dansylacetamidooxyamine (DNSAOA)-LC-fluorescence method for the determination of aqueous-phase glyoxal (GL), methylglyoxal (MG) and hydroxyacetaldehyde (HA). As derivatization of dicarbonyls can potentially lead to complex mixtures, a thorough study of the reaction patterns of GL and MG with DNSAOA was carried out. Derivatization of GL and MG was shown to follow the kinetics of successive reactions, yielding predominantly doubly derivatized compounds. We verified that the bis-DNSAOA structure of these adducts exerted only minor influence on their fluorescence properties. Contrary to observations made with formaldehyde, derivatization of GL, MG and, to a lesser extent of HA, was shown to be faster in acidic (H 2 SO 4) medium with a maximum of efficiency for acid concentrations of ca. 2.5 mM. Concomitant separation of GL, MG, HA and of single carbonyls was achieved within 20 min by using C 18 chromatography and a gradient of CH 3 CN in water. Detection limits of 0.27, 0.17 and 0.12 nM were determined for GL, MG and HA, respectively. Consequently, low sample volumes are sufficient and, unlike numerous published methods, neither preconcentration nor large injection volumes are necessary to monitor trace-level samples. The method shows relative measurement uncertainties better than ±15% at the 95% level of confidence and good dynamic ranges (R 2 > 0.99) from 0.01 to 1.5 M for all carbonyls. GL, MG and HA were identified for the first time in polar snow samples, but also in saline frost flowers for which unexpected levels of 0.1-0.6 M were measured. Concentrations in the 0.02-2.3 M range were also measured in cloud water. In most samples, a predominance of HA over GL and MG was observed

Formaldehyde in the Alaskan Arctic snowpack: Partitioning and physical processes involved in air-snow exchanges

International audienceThe snowpack is a photochemically active medium which produces numerous key reactive species involved in the atmospheric chemistry of polar regions. Formaldehyde (HCHO) is one such reactive species produced in the snow, and which can be released to the atmospheric boundary layer. Based on atmospheric and snow measurements, this study investigates the physical processes involved in the HCHO air-snow exchanges observed during the OASIS 2009 field campaign at Barrow, Alaska. HCHO concentration changes in a fresh diamond dust layer are quantitatively explained by the equilibration of a solid solution of HCHO in ice, through solid-state diffusion of HCHO within snow crystals. Because diffusion of HCHO in ice is slow, the size of snow crystals is a major variable in the kinetics of exchange and the knowledge of the snow specific surface area is therefore crucial. Air-snow exchanges of HCHO can thus be explained without having to consider processes taking place in the quasi-liquid layer present at the surface of ice crystals. A flux of HCHO to the atmosphere was observed simultaneously with an increase of HCHO concentration in snow, indicating photochemical production in surface snow. This study also suggests that the difference in bromine chemistry between Alert (Canadian Arctic) and Barrow leads to different snow composition and post-deposition evolutions. The highly active bromine chemistry at Barrow probably leads to low HCHO concentrations at the altitude where diamond dust formed. Precipitated diamond dust was subsequently undersaturated with respect to thermodynamic equilibrium, which contrasts to what was observed elsewhere in previous studies

Formaldehyde in the Alaskan Arctic snowpack: Partitioning and physical processes involved in air-snow exchanges

International audienceThe snowpack is a photochemically active medium which produces numerous key reactive species involved in the atmospheric chemistry of polar regions. Formaldehyde (HCHO) is one such reactive species produced in the snow, and which can be released to the atmospheric boundary layer. Based on atmospheric and snow measurements, this study investigates the physical processes involved in the HCHO air-snow exchanges observed during the OASIS 2009 field campaign at Barrow, Alaska. HCHO concentration changes in a fresh diamond dust layer are quantitatively explained by the equilibration of a solid solution of HCHO in ice, through solid-state diffusion of HCHO within snow crystals. Because diffusion of HCHO in ice is slow, the size of snow crystals is a major variable in the kinetics of exchange and the knowledge of the snow specific surface area is therefore crucial. Air-snow exchanges of HCHO can thus be explained without having to consider processes taking place in the quasi-liquid layer present at the surface of ice crystals. A flux of HCHO to the atmosphere was observed simultaneously with an increase of HCHO concentration in snow, indicating photochemical production in surface snow. This study also suggests that the difference in bromine chemistry between Alert (Canadian Arctic) and Barrow leads to different snow composition and post-deposition evolutions. The highly active bromine chemistry at Barrow probably leads to low HCHO concentrations at the altitude where diamond dust formed. Precipitated diamond dust was subsequently undersaturated with respect to thermodynamic equilibrium, which contrasts to what was observed elsewhere in previous studies

Soluble, light-absorbing species in snow at Barrow, Alaska

International audienceAs part of the international multidisciplinary Ocean - Atmosphere - Sea Ice - Snowpack (OASIS) program we analyzed more than 500 terrestrial (melted) snow samples near Barrow, AK between February and April 2009 for light absorption, as well as H2O2 and inorganic anion concentrations. For light absorption in the photochemically active region (300-450 nm) of surface snows, H2O2 and NO3− make minor contributions (combined < 9% typically), while HUmic LIke Substances (HULIS) and unknown chromophores each account for approximately half of the total absorption. We have identified four main sources for our residual chromophores (i.e., species other than H2O2 or NO3−): (1) vegetation and organic debris impact mostly the lowest 20 cm of the snowpack, (2) marine inputs, which are identified by high Cl− and SO42− contents, (3) deposition of diamond dust to surface snow, and (4) gas-phase exchange between the atmosphere and surface snow layers. The snow surfaces, and accompanying chromophore concentrations, are strongly modulated by winds and snowfall at Barrow. However, even with these physical controls on light absorption, we see an overall decline of light absorption in near-surface snow during the 7 weeks of our campaign, likely due to photo-bleaching of chromophores. While HULIS and unknown chromophores dominate light absorption by soluble species in Barrow snow, we know little about the photochemistry of these species, and thus we as a community are probably overlooking many snowpack photochemical reactions