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Environ Sci Technol

Title:		Estimation of membrane diffusion coefficients and equilibration times for low-density polyethylene passive diffusion samplers
Author(s):		Divine CE; McCray JE;
Address:		"Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado 80401, USA. cdivine@mines.edu"
Journal Title:		Environ Sci Technol
Year:		2004
Volume:		38
Issue:		6
Page Number:		1849 - 1857
DOI:		10.1021/es034695q
ISSN/ISBN:		0013-936X (Print) 0013-936X (Linking)
Abstract:		"Passive diffusion (PD) samplers offer several potential technical and cost-related advantages, particularly for measuring dissolved gases and volatile organic compounds (VOCs) in groundwater at contaminated sites. Sampler equilibration is a diffusion-type process; therefore, equilibration time is dependent on sampler dimensions, membrane thickness, and the temperature-dependent membrane diffusion coefficient (Dm) for the analyte of interest. Diffusion coefficients for low-density polyethylene membranes were measured for He, Ne, H2, O2, and N2 in laboratory experiments and ranged from 1.1 to 1.9 x 10(-7) cm2 sec(-1) (21 degrees C). Additionally, Dm values for several commonly occurring VOCs were estimated from empirical experimental data previously presented by others (Vroblesky, D. A.; Campbell, T. R. Adv. Environ. Res. 2001, 5(1), 1.), and estimated values ranged from 1.7 to 4.4 x 10(-7) cm2 sec(-1) (21 degrees C). On the basis of these Dm ranges, PD sampler equilibration time is predicted for various sampler dimensions, including dimensions consistent with simple constructed samplers used in this study and commercially available samplers. Additionally, a numerical model is presented that can be used to evaluate PD sampler concentration 'lag time' for conditions in which in situ concentrations are temporally variable. The model adequately predicted lag time for laboratory experiments and is used to show that data obtained from appropriately designed PD samplers represent near-instantaneous measurement of in situ concentrations for most field conditions"
Keywords:		"Diffusion Environmental Monitoring/*instrumentation/methods Forecasting Membranes, Artificial *Models, Theoretical Polyethylene Trace Elements/*analysis Water Pollutants, Chemical/*analysis;"
Notes:		"MedlineDivine, Craig E McCray, John E eng 2004/04/13 Environ Sci Technol. 2004 Mar 15; 38(6):1849-57. doi: 10.1021/es034695q"