Oxyanion flux characterization using passive flux meters: Development and field testing of surfactant-modified granular activated carbon

Abstract We report here on the extension of Passive Flux Meter (PFM) applications for measuring fluxes of oxyanions in groundwater, and present results for laboratory and field studies. Granular activated carbon, with and without impregnated silver (GAC and SI-GAC, respectively), was modified with a cationic surfactant, hexadecyltrimethylammonium (HDTMA), to enhance the anion exchange capacity (AEC). Langmuir isotherm sorption maxima for oxyanions measured in batch experiments were in the following order: perchlorate NN chromate N selenate, consistent with their selectivity. Linear sorption isotherms for several alcohols suggest that surfactant modification of GAC and SI-GAC reduced (∼ 30-45%) sorption of alcohols by GAC. Water and oxyanion fluxes (perchlorate and chromate) measured by deploying PFMs packed with surfactant-modified GAC (SM-GAC) or surfactant-modified, silver-impregnated GAC (SM-SI-GAC) in laboratory flow chambers were in close agreement with the imposed fluxes. The use of SM-SI-GAC as a PFM sorbent was evaluated at a field site with perchlorate contamination of a shallow unconfined aquifer. PFMs packed with SM-SI-GAC were deployed in three existing monitoring wells with a perchlorate concentration range of ∼ 2.5 to 190 mg/L. PFM-measured, depth-averaged, groundwater fluxes ranged from 1.8 to 7.6 cm/day, while depth-averaged perchlorate fluxes varied from 0.22 to 1.7 g/m 2 /day. Groundwater and perchlorate flux distributions measured in two PFM deployments closely matched each other. Depth-averaged Darcy fluxes measured with PFMs were in line with an estimate from a borehole dilution test, but much smaller than those based on hydraulic conductivity and head gradients; this is likely due to flow divergence caused by well-screen clogging. Flux-averaged perchlorate concentrations measured with PFM deployments matched concentrations in groundwater samples taken from one well, but not in two Journal of Contaminant Hydrology 92 (2007) other wells, pointing to the need for additional field testing. Use of the surfactant-modified GACs for measuring fluxes of other anions of environmental interest is discussed

Controlling the structure of sequence-defined poly ( phosphodiester)s for optimal MS/MS reading of digital information

International audienc

From:E to Z and back again: Reversible photoisomerisation of an isolated charge-tagged azobenzene

Substituted azobenzenes serve as chromophores and actuators in a wide range of molecular photoswitches. Here, tandem ion mobility spectrometry coupled with laser excitation is used to investigate the photoisomerisation of selected E and Z isomers of the charge-tagged azobenzene, methyl orange. Both isomers display a weak S1(nπ∗) photoisomerisation response in the blue part of the spectrum peaking at 440 nm and a more intense S2(ππ∗) photoisomerisation response in the near-UV with maxima at 370 and 310 nm for the E and Z isomers, respectively. The 60 nm separation between the S2(ππ∗) photo-response maxima for the two isomers allows them to be separately addressed in the gas phase and to be reversibly photoisomerised using different colours of light. This is an essential characteristic of an ideal photoswitch. The study demonstrates that a sequence of light pulses at different stages in an ion mobility spectrometer can be deployed to generate and probe isomers that cannot be electrosprayed directly from solution or produced through collisions in the ion source

Minority energy assessment report

The purpose of this research is to project household energy consumption, energy expenditure, and energy expenditure as share of income for five population groups from 1991 to 2009. The approach uses the Minority Energy Assessment Model (MEAM), developed by Argonne National Laboratory for the US Department of Energy's Office of Minority Economic Impact. The MEAM provides a framework that can be used to forecast regional energy consumption and energy expenditure for majority, black, Hispanic, poor, and nonpoor households. The forecasts of key macroeconomic and energy variables used as exogenous variables in the MEAM were obtained from the Data Resources, Inc., Macromodel and Energy Model. Generally, the projections of household energy consumption, expenditure, and energy expenditure as share of income vary across population groups and census regions