Passive Sampling Techniques Episode 8 pdf

Chapter 10Membrane-enclosed sorptive coating for the monitoring of organic compounds in water Albrecht Paschke, Branislav Vrana, Peter Popp, Luise Wennrich, Heidrun Paschke and Gerrit Sc

Chapter 10

Membrane-enclosed sorptive coating for the monitoring of organic

compounds in water

Albrecht Paschke, Branislav Vrana, Peter Popp,

Luise Wennrich, Heidrun Paschke and Gerrit Schu¨u¨rmann

Membrane-enclosed sorptive coating (MESCO) denotes the recently developed miniaturised passive sampling devices consisting of a mem-brane which encloses polydimethylsiloxane (PDMS) coatings or coarse silicone material (embedded in a fluid) as the collecting phase for organic compounds.1The general advantages of the MESCO samplers are (i) the simple and loss-free separation of the collector phase; (ii) its processing without further clean-up steps by direct thermal desorption

or solvent microextraction; (iii) the possibility to spike the collecting phase before deployment with so-called performance reference com-pounds (PRCs) and (iv) that, in addition to chemical target or non-target analysis, the collecting phase can also be subject to biological effect screening (after digestion using an appropriate solvent)

In our work we took advantage of commercially available PDMS coat-ings or silicone materials as the collecting phase PDMS is recommended

as a receiving phase in extraction and thermodesorption as it has a number of benefits compared with other sorbents [1] The predominant mechanism of analyte extraction into PDMS/silicone phase is absorptive partitioning which has the advantage that displacement effects of the analytes (competitive enrichment), characteristic for adsorbents, play no role

1

When neat silicone material is used as collecting phase instead of a sorptive coating, one can take the abbreviation MESCO also for membrane-enclosed silicone collector.

Comprehensive Analytical Chemistry 48

R Greenwood, G Mills and B Vrana (Editors)

Volume 48 ISSN: 0166-526X DOI: 10.1016/S0166-526X(06)48010-7

TABLE 10.2

Sampling rates (R S ) of different MESCO II configurations (SR—silicone rod; ST––silicone tube) for selected priority pollutants determined in various laboratory experiments

SR+water in

100 mm LDPEa (mL h
1)

RSof ST+water in

100 mm LDPEa (mL h
1)

RSof ST+air in

100 mm LDPEa (mL h
1)

RSof SR+air in

100 mm LDPEb (mL h
1)

RSof SR+air in

50 mm LDPEb (mL h
1)

a Determined in a flow-through apparatus with a nominal analyte concentration of 50 ng L–1at 141C [9]

b Determined in serial batch extraction tests with a nominal analyte concentration of 25 ng L
1at room temperature [14]

c Substance abbreviations: HCH––hexachlorocyclohexane; TCB—tetrachlorobenzene; PCB—polychlorinated biphenyl.

d Distribution constant (KSW¼ CMESCO(eq.)/CW(eq.)) calculated by assuming that CW(eq.) ¼ 25 ng L
1

e Not determined.

f Potential outlier.

TABLE 10.3

Average mass of pollutants (in pg per Twister bar) determined in the control MESCOs (m 0 ) and in the field-exposed MESCOs (m S ; n ¼ 3), and in situ aqueous concentrations of organic analytes estimated from MESCO (C W )

The samplers were exposed 28 days in August 2002 at a site in the river Weisse Elster in Saxony-Anhalt, Germany.

a CV, coefficient of variation or relative standard deviation of multiple samples.

Chapter 11

In situ monitoring and dynamic

speciation measurements in solution using DGT

Kent W Warnken, Hao Zhang and William Davison

Diffusive gradients in thin-films (DGT) was first used in the mid-1990s

as an in situ technique for dynamic trace metal speciation measure-ments[1,2] It has since been developed as a general monitoring tool for

a wide range of analytes in addition to the transition and heavy metals originally measured, including the major cations, Ca and Mg[3], stable isotopes of Cs and Sr[4], radionuclides of Cs[5]and Tc [6], phosphate [7]and sulphide[8] In a comprehensive study, Garmoet al.[9] demo-nstrated the capabilities of DGT to measure 55 elements with a Chelexs 100-based resin-gel

As its name implies, DGT relies on the quantitative diffusive trans-port of solutes across a well-defined gradient in concentration, typically established within a layer of hydrogel and outer filter membrane The filter membrane is exposed directly to the deployment solution and acts

as a protective layer for the diffusive gel Once diffusing through these outer layers, solutes are irreversibly removed or chelated at the back side of the diffusive gel by a selective binding agent, typically Chelex

100, which is immobilized in a second layer of hydrogel The hydrogels used in DGT are typically made of polyacrylamide, which can be fab-ricated with a range of properties, including almost unimpeded diffu-sion due to the gel having a water content as high as 95%[10]

The pre-filter, diffusive gel and binding-gel layers are assembled into

an all plastic sampling device comprised of a base and cap (Fig 11.1) The cap is push-fit onto the base to provide a water-tight seal and has an opening or ‘viewing window’ that exposes a known area of the filter

to the deployment solution The theoretical basis for the use of DGT Comprehensive Analytical Chemistry 48

R Greenwood, G Mills and B Vrana (Editors)

Volume 48 ISSN: 0166-526X DOI: 10.1016/S0166-526X(06)48011-9