Christos Kaltsonoudis

Analysis of carbendazim and thiabendazole in lemons by CE-DAD

SummaryA capillary electrophoretic method for the determination of two benzimidazole fungicides, carbendazim and thiabendazole, in lemons has been developed. The two fungicides were separated in a law-pH phosphate buffer containing acetonitrile. Reproducibility tests measuring both migration times and peak areas gave low relative standard-deviation values. Calibration graphs were linear and the detection limits, defined as a signal-to-noise ratio of 3:1, were 2.3 and 2.0 μg mL−1 for thiabendazole and carbendazim, respectively. Analysis of carbendazim and thiabendazole residues in lemons was performed after lemon homogenization, extraction with ethyl acetate and purification through a series of separatory-funnel, acid-base partitions. This lemon clean-up procedure ensured no interference in the capillary electrophoretic analysis from lemon endogenous ingredients.

A new sample clean-up procedure, based on ion-pairing on RP-SPE cartridges, for the determination of ionizable pesticides

Residues of ionizable pesticides in lemon extracts were isolated by a new solid-phase extraction method on reverse-phase cartridges. Cartridges were preconditioned with zwittergents such as cetyltrimethylammonium bromide for anionic pesticides and sodium dodecyl sulphate for cationic pesticides. Zwittergents and opposite charged analytes produce ion pairs that are stronger retained on the cartridge bed than the native analytes. Following washings of the cartridge, with an eluent of suitable concentration in organic solvent, resulted in interference removal. Finally, pesticides were eluted with acetonitrile. Based on the aforementioned procedure, two analytical methods were developed for the determination of acidic (2,4,5-trichlorophenoxyacetic acid, dichlorprop, and dinoseb) and basic (carbendazim and thiabendazole) pesticide residues in lemons. The analytes were separated on a reverse-phase C18 HPLC column and detected by UV.

Spatial Variability of Sources and Mixing State of Atmospheric Particles in a Metropolitan Area

Characterizing intracity variations of atmospheric particulate matter has mostly relied on fixed-site monitoring and quantifying variability in terms of different bulk aerosol species. In this study, we performed ground-based mobile measurements using a single-particle mass spectrometer to study spatial patterns of source-specific particles and the evolution of particle mixing state in 21 areas in the metropolitan area of Pittsburgh, PA. We selected sampling areas based on traffic density and restaurant density with each area ranging from 0.2 to 2 km2. Organics dominate particle composition in all of the areas we sampled while the sources of organics differ. The contribution of particles from traffic and restaurant cooking varies greatly on the neighborhood scale. We also investigate how primary and aged components in particles mix across the urban scale. Lastly we quantify and map the particle mixing state for all areas we sampled and discuss the overall pattern of mixing state evolution and its implications. We find that in the upwind and downwind of the urban areas, particles are more internally mixed while in the city center, particle mixing state shows large spatial heterogeneity that is mostly driven by emissions. This study is to our knowledge, the first study to perform fine spatial scale mapping of particle mixing state using ground-based mobile measurement and single-particle mass spectrometry.

Estimation of the volatility distribution of organic aerosol combining thermodenuder and isothermal dilution measurements

10 A method is developed following the work of Grieshop et al. (2009) for the determination of the organic aerosol (OA) volatility distribution combining thermodenuder and isothermal dilution measurements. The approach was tested in experiments that were conducted in a smog chamber using organic aerosol (OA) produced during meat charbroiling. A thermodenuder (TD) was operated at temperatures ranging from 25 to 250 o C with a 14 s 15 centerline residence time coupled to a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Scanning Mobility Particle Sizer (SMPS). In parallel, a dilution chamber filled with clean air was used to dilute isothermally the aerosol of the larger chamber by approximately a factor of 10. The OA mass fraction remaining was measured as a function of temperature in the TD and as a function of time in the isothermal dilution 20 chamber. These two sets of measurements were used together to estimate the volatility distribution of the OA and its effective vaporization enthalpy and accommodation coefficient. In the isothermal dilution experiments approximately 20% of the OA evaporated within 15 min. Almost all the OA evaporated in the TD at approximately 200 o C. The resulting volatility distributions suggested that around 60-75% of the cooking OA (COA) at concentrations 25 around 500 μg m -3 consisted of low volatility organic compounds (LVOCs), 20-30% of semivolatile organic compounds (SVOCs) and around 10% of intermediate volatility organic compounds (IVOCs). The estimated effective vaporization enthalpy of COA was 100 ± 20 kJ mol -1 and the effective accommodation coefficient was 0.06-0.07. Addition of the dilution measurements to the TD data results in a lower uncertainty of the estimated vaporization 30 enthalpy as well as the SVOC content of the OA.