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 10.1 INTRODUCTION 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. 1 The 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 t ook advantage of commercially available PDMS coat- ings or silicone materials as the collect ing phase. PDMS is recommended as a receiving phase i n extraction a nd thermodesorption as it has a number of benefits compared with other sorbents [1].Thepredominant mechanism of analyte extraction into PDMS/silicone phase is absorptive partitioning which has the advantage that displaceme nt 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 r 2007 Elsevier B.V. All rights reserved. 231 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 Substance R S of SR+water in 100 mm LDPE a (mL h À1 ) R S of ST+water in 100 mm LDPE a (mL h À1 ) R S of ST+air in 100 mm LDPE a (mL h À1 ) R S of SR+air in 100 mm LDPE b (mL h À1 ) R S of SR+air in 50 mm LDPE b (mL h À1 ) a-HCH c 0.28 0.18 0.14 0.031 d 0.039 d 1,2,3,4-TCB c not det. e not det. e not det. e 1.47 0.61 Pentachlorobenzene 0.21 0.19 4.30 1.30 2.24 Hexachlorobenzene 0.09 0.06 0.90 0.65 0.87 Naphthalene not det. e not det. e not det. e 0.13 d not det. e Acenaphthylene 0.51 0.73 1.40 0.07 d not det. e Acenaphthene 0.48 0.67 2.23 0.35 not det. e Fluorene 0.75 1.34 1.88 0.49 not det. e Phenanthrene 0.26 0.27 0.93 0.63 0.72 Anthracene 0.13 0.26 0.99 0.40 0.83 Fluoranthene 0.04 0.06 0.12 0.33 0.26 Pyrene 0.03 0.03 0.10 0.26 0.23 PCB 28 c 0.06 0.06 0.92 0.74 0.63 PCB 52 0.03 0.04 0.62 0.66 4.12 f PCB 101 0.004 not det. e not det. e 0.39 not det. e PCB 138 not det. e not det. e not det. e 0.14 0.05 PCB 153 not det. e not det. e not det. e 0.15 0.05 a Determined in a flow-through apparatus with a nominal analyte concentration of 50 ng L –1 at 141C [9]. b Determined in serial batch extraction tests with a nominal analyte concentration of 25 ng L À1 at room temperature [14]. c Substance abbreviations: HCH––hexachlorocyclohexane; TCB—tetrachlorobenzene; PCB—polychlorinated biphenyl. d Distribution constant (K SW ¼ C MESCO( eq.)/C W( eq.)) calculated by assuming that C W( eq.) ¼ 25 ng L À1 . e Not determined. f Potential outlier. A. Paschke et al. 238 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 ) Compound m 0 (pg) CV a (n ¼ 4) (%) m s (pg) CV (n ¼ 3) (%) k e (day –1 )C W (ng L À1 ) HCB 1 13 79 2 0.085 0.14 g-HCH 1.8 1695 27 0.130 182 p,p 0 -DDE o1 132 8 0.069 0.03 PCB 28 1 16 62 7 0.077 0.05 PCB 52 o1 43 6 0.072 0.02 PCB 101 o1 27 12 0.065 0.004 PCB 138 o1 33 5 0.062 0.003 PCB 153 o1 22 9 0.062 0.002 PCB 180 o1 8 10 0.064 0.001 Acenaphthylene 4 45 124 11 0.107 2.16 Acenaphthene 10 10 1172 3 0.102 12.2 Fluorene 18 9 1128 4 0.100 9.76 Anthracene 8 30 1494 9 0.094 7.03 Phenanthrene 62 30 3128 7 0.094 15.4 Fluoranthene 13 30 3135 8 0.079 2.86 Pyrene 13 15 3302 8 0.076 2.16 Benzo[a]anthracene 2 76 1185 3 0.069 0.32 Chrysene 4 42 967 2 0.063 0.10 Benzo[b]fluoranthene o5 450 1 0.071 0.15 Benzo[k]fluoranthene o5 244 3 0.068 0.06 Benzo[a]pyrene o5 455 4 0.067 0.09 Indeno[1,2,3-cd]pyrene o5 121 7 0.087 0.29 Dibenzo[a,h]anthracene o5 46 10 0.084 0.03 Benzo[g,h,i]perylene o5 115 10 0.076 0.20 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. MESCO for monitoring in water 241 Chapter 11 In situ monitoring and dynamic speciation measurements in solution using DGT Kent W. Warnken, Hao Zhang and William Davison 11.1 INTRODUCTION 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, Garmo et al. [9] demo- nstrated the capabilities of DGT to measure 55 elements with a Chelex s 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 r 2007 Elsevier B.V. All rights reserved. 251 . L À1 ) HCB 1 13 79 2 0. 085 0.14 g-HCH 1 .8 1695 27 0.130 182 p,p 0 -DDE o1 132 8 0.069 0.03 PCB 28 1 16 62 7 0.077 0.05 PCB 52 o1 43 6 0.072 0.02 PCB 101 o1 27 12 0.065 0.004 PCB 1 38 o1 33 5 0.062 0.003 PCB. 0.002 PCB 180 o1 8 10 0.064 0.001 Acenaphthylene 4 45 124 11 0.107 2.16 Acenaphthene 10 10 1172 3 0.102 12.2 Fluorene 18 9 11 28 4 0.100 9.76 Anthracene 8 30 1494 9 0.094 7.03 Phenanthrene 62 30 31 28 7. 8 0.079 2 .86 Pyrene 13 15 3302 8 0.076 2.16 Benzo[a]anthracene 2 76 1 185 3 0.069 0.32 Chrysene 4 42 967 2 0.063 0.10 Benzo[b]fluoranthene o5 450 1 0.071 0.15 Benzo[k]fluoranthene o5 244 3 0.068