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The diffusive gradients in thin films (DGT) technique is an environmental chemistry technique for the detection of elements and compounds in aqueous environments, including natural waters,^[1] sediments^[2] and soils.^[3] It is well suited to in situ detection of bioavailable toxic trace metal contaminants.^[4]^[5]^[6] The technique involves using a specially-designed passive sampler that houses a binding gel, diffusive gel and membrane filter. The element or compound passes through the membrane filter and diffusive gel and is assimilated by the binding gel in a rate-controlled manner. Post-deployment analysis of the binding gel can be used to determine the time-weighted-average bulk solution concentration of the element or compound via a simple equation.

History

The DGT technique was developed in 1994 by Hao Zhang and William Davison at the Lancaster Environment Centre of Lancaster University in the United Kingdom. The technique was first used to detect metal cations in marine environments using Chelex 100 as the binding agent. Further characterisation of DGT, including the results of field deployments in the Menai Strait and the North Atlantic Ocean, was published in 1995.^[7] The technique was first tested in soils in 1998, with results demonstrating that kinetics of dissociation of labile species in the porewater (soil solution) could be determined via DGT.^[8] Since then, the DGT technique has been modified and expanded to include a significant number of elements and compounds, including cationic metals,^[7] nitrate,^[9] phosphate and other oxyanions (V, Cr^VI, As, Se, Mo, Sb, W),^[2]^[10]^[11]^[12]^[13]^[14] antibiotics,^[15] bisphenols,^[16] and nanoparticles,^[17] and has even been modified for the geochemical exploration of gold.^[18] DGT has also been developed and calibrated for the measure of radionuclides, including for the analysis of actinides such as U, Pu, Am and Cm, both in the environment^[19] and even in cooling pools for spent nuclear fuel rods.^[20]

DGT Research Ltd. was established in July 1997 by the original developers of the technique, Profs. Davison and Zhang, and sells ready-made DGT® devices for water, soil and sediment deployments to measure different analytes, as well as the component parts for self-assembly. The company holds the original patents for the device and DGT® is a trademark which is registered throughout the world. In 2014 a rival company "EasySensor" was set up by Prof. Shiming Ding and supplies devices that the company claims are analogous to the original DGT® products.^[21]

The DGT device

The most commonly used DGT device is a plastic "piston-type" probe, and comprises a cylindrical polycarbonate base and a tight-fitting, circular cap with an opening (DGT window). A binding gel, diffusive gel (typically a polyacrylamide hydrogel) and filter membrane are stacked onto the base, and the cap is used to seal the gel and filter layers inside^[4]^: 4.2.3 Dimensions of the gel layers vary depending on features of the environment, such as the flow rate of water being sampled;^[4]^: 4.2.1 an example is an approximately 2 cm device diameter containing a 1mm gel layer.^[22] Other commonly used probe configurations include those for deploying in sediments (to measure solute mobilisation with depth)^[23] and in planar form for measuring solute dynamics in the plant rhizosphere.^[24]

Principles of operation

Deployment

DGT devices can be directly deployed in aqueous environmental media, including natural waters, sediments, and soils.^[1] In fast-flowing waters, the DGT device's face should be perpendicular to the direction of flow, in order to ensure the diffusive boundary layer (DBL) is not affected by laminar flow. In slow-flowing or stagnant waters such as in ponds or groundwater, deployment of DGT devices with different thicknesses of diffusive gel can allow for the determination of the DBL and a more accurate determination of bulk concentration.^[4]^: 4.2.1^[25]^[9] Modifications to the diffusive gel (e.g. increasing or decreasing the thickness) can also be undertaken to ensure low detection limits.^[26]

Analysis of binding gels and chemical imaging

After the DGT devices/probes have been retrieved, the binding gels can be eluted using methods that depend on the target analyte and the DGT binding gel (for example, nitric acid can be used to elute most metal cations from Chelex-100 gels).^[4]^: 4.2.1 NaOH can be used to elute most oxyanions from Zr-Oxide(Ding et al., 2010, 2011,2016; Sun et al.,2014).The eluent can then be quantitatively analysed via a range of analytical techniques, including but not limited to: ICP-MS, GFAAS^[4]^: 4.2.1 ICP-OES, AAS,^[22] UV-Vis spectroscopy or computer imaging densitometry.^[27] For chemical imaging and to obtain two-dimensional (2D) sub-mm high resolution distribution of analytes in heterogenous environments, such as sediments and the rhizosphere, the retrieved gel strips can be analyzed by PIXE or LA-ICP-MS after gel drying.^[12]^[28]^[29]^[30]^[31]

The DGT equation

DGT is based on the application of Fick's law.^[22] Once the mass of an analyte has been determined, the time-averaged concentration of the analyte in the bulk, $C_{DGT}$ , can be determined by application of the following equation:

C_{DGT}={\frac {M\Delta g}{DtA}}\

where $M$ is the mass of the analyte on the resin, $\Delta g$ is the combined thickness of the hydrogel layer and filter membrane (i.e. the "diffusion layer"). The previously determined diffusion coefficient of the analyte in the type of diffusion layer used and at the ambient temperature is represented by $D$ ^[32], $t$ is the deployment time, and $A$ is the area of the DGT window.^[4]^: Eq.2 More elaborate analysis techniques may be required in cases where the ionic strength of the water is low and where significant organic matter is present.^[33]

References

^ ^a ^b Chaudhary M, Quanz M, Williams J, Maltby E, Oakes K, Spooner I, Walker TR (September 2020). "Assessment of metal(loid) concentrations using Diffusive Gradient Thin (DGT) films in marine, freshwater and wetland aquatic ecosystems impacted by industrial effluents". Case Studies in Chemical and Environmental Engineering. 2: 100041. doi:10.1016/j.cscee.2020.100041.
^ ^a ^b Zhang H, Davison W, Gadi R, Kobayashi T (August 1998). "In situ measurement of dissolved phosphorus in natural waters using DGT". Analytica Chimica Acta. 370 (1): 29–38. doi:10.1016/S0003-2670(98)00250-5.
^ Wilkins CL (October 1983). "Hyphenated techniques for analysis of complex organic mixtures". Science. 222 (4621): 291–6. Bibcode:1983Sci...222..291W. doi:10.1126/science.6353577. PMID 6353577.
^ ^a ^b ^c ^d ^e ^f ^g "Diffusive Gradients in Thin-films (DGT): A Technique for Determining Bioavailable Metal Concentrations" (PDF). International Network for Acid Prevention. March 2002. Archived from the original (PDF) on 28 February 2015. Retrieved 23 April 2015.
^ Strivens J, Hayman N, Johnston R, Rosen G (May 2019). "Effects of Dissolved Organic Carbon on Copper Toxicity to Embryos of Mytilus galloprovincialis as Measured by Diffusive Gradient in Thin Films". Environmental Toxicology and Chemistry. 38 (5): 1029–1034. doi:10.1002/etc.4404. PMID 30840314. S2CID 73466599.
^ Strivens J, Hayman N, Rosen G, Myers-Pigg A (April 2020). "Toward Validation of Toxicological Interpretation of Diffusive Gradients in Thin Films in Marine Waters Impacted by Copper". Environmental Toxicology and Chemistry. 39 (4): 873–881. doi:10.1002/etc.4673. PMID 32004383.
^ ^a ^b Zhang H, Davison W (October 1995). "Performance Characteristics of Diffusion Gradients in Thin Films for the in Situ Measurement of Trace Metals in Aqueous Solution". Analytical Chemistry. 67 (19): 3391–3400. doi:10.1021/ac00115a005.
^ Harper MP, Davison W, Zhang H, Tych W (August 1998). "Kinetics of metal exchange between solids and solutions in sediments and soils interpreted from DGT measured fluxes". Geochimica et Cosmochimica Acta. 62 (16): 2757–2770. Bibcode:1998GeCoA..62.2757H. doi:10.1016/S0016-7037(98)00186-0.
^ ^a ^b Corbett, Thomas D. W.; Dougherty, Hannah; Maxwell, Bryan; Hartland, Adam; Henderson, William; Rys, Gerald J.; Schipper, Louis A. (2020-05-20). "Utility of 'Diffusive Gradients in Thin-Films' for the measurement of nitrate removal performance of denitrifying bioreactors". Science of the Total Environment. 718: 135267. doi:10.1016/j.scitotenv.2019.135267. ISSN 0048-9697. PMID 31859060. S2CID 209425982.
^ Santner J, Prohaska T, Luo J, Zhang H (September 2010). "Ferrihydrite containing gel for chemical imaging of labile phosphate species in sediments and soils using diffusive gradients in thin films". Analytical Chemistry. 82 (18): 7668–74. doi:10.1021/ac101450j. PMC 3432420. PMID 20735010.
^ Luo J, Zhang H, Santner J, Davison W (November 2010). "Performance characteristics of diffusive gradients in thin films equipped with a binding gel layer containing precipitated ferrihydrite for measuring arsenic(V), selenium(VI), vanadium(V), and antimony(V)". Analytical Chemistry. 82 (21): 8903–9. doi:10.1021/ac101676w. PMID 20936784.
^ ^a ^b Guan DX, Williams PN, Luo J, Zheng JL, Xu HC, Cai C, Ma LQ (March 2015). "Novel precipitated zirconia-based DGT technique for high-resolution imaging of oxyanions in waters and sediments". Environmental Science & Technology. 49 (6): 3653–61. Bibcode:2015EnST...49.3653G. doi:10.1021/es505424m. PMID 25655234.
^ Stockdale A, Davison W, Zhang H (April 2010). "2D simultaneous measurement of the oxyanions of P, V, As, Mo, Sb, W and U" (PDF). Journal of Environmental Monitoring. 12 (4): 981–4. doi:10.1039/b925627j. PMID 20383381.
^ Pan Y, Guan DX, Zhao D, Luo J, Zhang H, Davison W, Ma LQ (December 2015). "Novel Speciation Method Based on Diffusive Gradients in Thin-Films for in Situ Measurement of Cr(VI) in Aquatic Systems". Environmental Science & Technology. 49 (24): 14267–73. Bibcode:2015EnST...4914267P. doi:10.1021/acs.est.5b03742. PMID 26535488.
^ Chen CE, Zhang H, Jones KC (May 2012). "A novel passive water sampler for in situ sampling of antibiotics". Journal of Environmental Monitoring. 14 (6): 1523–30. doi:10.1039/c2em30091e. PMID 22538362.
^ Zheng JL, Guan DX, Luo J, Zhang H, Davison W, Cui XY, et al. (January 2015). "Activated charcoal based diffusive gradients in thin films for in situ monitoring of bisphenols in waters". Analytical Chemistry. 87 (1): 801–7. doi:10.1021/ac503814j. PMID 25412473.
^ Pouran HM, Martin FL, Zhang H (June 2014). "Measurement of ZnO nanoparticles using diffusive gradients in thin films: binding and diffusional characteristics". Analytical Chemistry. 86 (12): 5906–13. doi:10.1021/ac500730s. hdl:2436/621804. PMID 24831848.
^ Lucas A, Rate A, Zhang H, Salmon SU, Radford N (August 2012). "Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters". Analytical Chemistry. 84 (16): 6994–7000. doi:10.1021/ac301003g. PMID 22812590.
^ Chaplin J, Warwick P, Cundy A, Bochud F, Froidevaux P (25 August 2021). "Novel DGT Configurations for the Assessment of Bioavailable Plutonium, Americium, and Uranium in Marine and Freshwater Environments". Analytical Chemistry. 93 (35): 11937–11945. doi:10.1021/acs.analchem.1c01342. PMID 34432435. S2CID 237307309.
^ Chaplin J, Christl M, Straub M, Bochud F, Froidevaux P (2 June 2022). "Passive Sampling Tool for Actinides in Spent Nuclear Fuel Pools". ACS Omega. 7 (23): 20053−20058. doi:10.1021/acsomega.2c01884. hdl:20.500.11850/554631. PMC 9202248. PMID 35722008. S2CID 249333570.
^ "global-easysensor.com". Archived from the original on 2020-08-08.
^ ^a ^b ^c Thomas P (1 July 2009). "Metals pollution tracing in the sewerage network using the diffusive gradients in thin films technique". Water Science and Technology. 60 (1): 65–70. doi:10.2166/wst.2009.287. PMID 19587403.
^ Zhang H, Davison W, Miller S, Tych W (1995-10-01). "In situ high resolution measurements of fluxes of Ni, Cu, Fe, and Mn and concentrations of Zn and Cd in porewaters by DGT". Geochimica et Cosmochimica Acta. 59 (20): 4181–4192. Bibcode:1995GeCoA..59.4181Z. doi:10.1016/0016-7037(95)00293-9. ISSN 0016-7037.
^ Williams PN, Santner J, Larsen M, Lehto NJ, Oburger E, Wenzel W, et al. (2014-08-05). "Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice". Environmental Science & Technology. 48 (15): 8498–506. Bibcode:2014EnST...48.8498W. doi:10.1021/es501127k. PMC 4124062. PMID 24967508.
^ Warnken KW, Zhang H, Davison W (June 2006). "Accuracy of the diffusive gradients in thin-films technique: diffusive boundary layer and effective sampling area considerations". Analytical Chemistry. 78 (11): 3780–7. doi:10.1021/ac060139d. PMID 16737237.
^ Lucas AR, Reid N, Salmon SU, Rate AW (October 2014). "Quantitative assessment of the distribution of dissolved Au, As and Sb in groundwater using the diffusive gradients in thin films technique". Environmental Science & Technology. 48 (20): 12141–9. Bibcode:2014EnST...4812141L. doi:10.1021/es502468d. PMID 25252140.
^ McGifford RW, Seen AJ, Haddad PR (March 2010). "Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films". Analytica Chimica Acta. 662 (1): 44–50. doi:10.1016/j.aca.2009.12.041. PMID 20152264.
^ Davison W, Fones GR, Grime GW (June 1997). "Dissolved metals in surface sediment and a microbial mat at 100-μm resolution". Nature. 387 (6636): 885–888. Bibcode:1997Natur.387..885D. doi:10.1038/43147. S2CID 4261454.
^ Warnken KW, Zhang H, Davison W (October 2004). "Analysis of polyacrylamide gels for trace metals using diffusive gradients in thin films and laser ablation inductively coupled plasma mass spectrometry". Analytical Chemistry. 76 (20): 6077–84. doi:10.1021/ac0400358. PMID 15481956.
^ Williams PN, Santner J, Larsen M, Lehto NJ, Oburger E, Wenzel W, et al. (5 August 2014). "Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice". Environmental Science & Technology. 48 (15): 8498–506. Bibcode:2014EnST...48.8498W. doi:10.1021/es501127k. PMC 4124062. PMID 24967508.
^ Hoefer C, Santner J, Puschenreiter M, Wenzel WW (April 2015). "Localized metal solubilization in the rhizosphere of Salix smithiana upon sulfur application". Environmental Science & Technology. 49 (7): 4522–9. Bibcode:2015EnST...49.4522H. doi:10.1021/es505758j. PMC 4394708. PMID 25782052.
^ Davison W, Zhang H. Diffusion Layer Properties. In: Davison W, ed. Diffusive Gradients in Thin-Films for Environmental Measurements. Cambridge Environmental Chemistry Series. Cambridge University Press; 2016:32-65.
^ Yabuki LN, Colaço CD, Menegário AA, Domingos RN, Kiang CH, Pascoaloto D (February 2014). "Evaluation of diffusive gradients in thin films technique (DGT) for measuring Al, Cd, Co, Cu, Mn, Ni, and Zn in Amazonian rivers". Environmental Monitoring and Assessment. 186 (2): 961–9. doi:10.1007/s10661-013-3430-x. PMID 24052239. S2CID 9781883.

External links

[Chaudhary_et_al_2020-1] Chaudhary M, Quanz M, Williams J, Maltby E, Oakes K, Spooner I, Walker TR (September 2020). "Assessment of metal(loid) concentrations using Diffusive Gradient Thin (DGT) films in marine, freshwater and wetland aquatic ecosystems impacted by industrial effluents". Case Studies in Chemical and Environmental Engineering. 2: 100041. doi:10.1016/j.cscee.2020.100041.

[Zhang_et_al_1998-2] Zhang H, Davison W, Gadi R, Kobayashi T (August 1998). "In situ measurement of dissolved phosphorus in natural waters using DGT". Analytica Chimica Acta. 370 (1): 29–38. doi:10.1016/S0003-2670(98)00250-5.

[pmid6353577-3] Wilkins CL (October 1983). "Hyphenated techniques for analysis of complex organic mixtures". Science. 222 (4621): 291–6. Bibcode:1983Sci...222..291W. doi:10.1126/science.6353577. PMID 6353577.

[inap-4] ^ ^a ^b ^c ^d ^e ^f ^g "Diffusive Gradients in Thin-films (DGT): A Technique for Determining Bioavailable Metal Concentrations" (PDF). International Network for Acid Prevention. March 2002. Archived from the original (PDF) on 28 February 2015. Retrieved 23 April 2015.

[5] Strivens J, Hayman N, Johnston R, Rosen G (May 2019). "Effects of Dissolved Organic Carbon on Copper Toxicity to Embryos of Mytilus galloprovincialis as Measured by Diffusive Gradient in Thin Films". Environmental Toxicology and Chemistry. 38 (5): 1029–1034. doi:10.1002/etc.4404. PMID 30840314. S2CID 73466599.

[6] Strivens J, Hayman N, Rosen G, Myers-Pigg A (April 2020). "Toward Validation of Toxicological Interpretation of Diffusive Gradients in Thin Films in Marine Waters Impacted by Copper". Environmental Toxicology and Chemistry. 39 (4): 873–881. doi:10.1002/etc.4673. PMID 32004383.

[Zhang_&_Davison_1995-7] Zhang H, Davison W (October 1995). "Performance Characteristics of Diffusion Gradients in Thin Films for the in Situ Measurement of Trace Metals in Aqueous Solution". Analytical Chemistry. 67 (19): 3391–3400. doi:10.1021/ac00115a005.

[8] Harper MP, Davison W, Zhang H, Tych W (August 1998). "Kinetics of metal exchange between solids and solutions in sediments and soils interpreted from DGT measured fluxes". Geochimica et Cosmochimica Acta. 62 (16): 2757–2770. Bibcode:1998GeCoA..62.2757H. doi:10.1016/S0016-7037(98)00186-0.

[:1-9] Corbett, Thomas D. W.; Dougherty, Hannah; Maxwell, Bryan; Hartland, Adam; Henderson, William; Rys, Gerald J.; Schipper, Louis A. (2020-05-20). "Utility of 'Diffusive Gradients in Thin-Films' for the measurement of nitrate removal performance of denitrifying bioreactors". Science of the Total Environment. 718: 135267. doi:10.1016/j.scitotenv.2019.135267. ISSN 0048-9697. PMID 31859060. S2CID 209425982.

[10] Santner J, Prohaska T, Luo J, Zhang H (September 2010). "Ferrihydrite containing gel for chemical imaging of labile phosphate species in sediments and soils using diffusive gradients in thin films". Analytical Chemistry. 82 (18): 7668–74. doi:10.1021/ac101450j. PMC 3432420. PMID 20735010.

[11] Luo J, Zhang H, Santner J, Davison W (November 2010). "Performance characteristics of diffusive gradients in thin films equipped with a binding gel layer containing precipitated ferrihydrite for measuring arsenic(V), selenium(VI), vanadium(V), and antimony(V)". Analytical Chemistry. 82 (21): 8903–9. doi:10.1021/ac101676w. PMID 20936784.

[:0-12] Guan DX, Williams PN, Luo J, Zheng JL, Xu HC, Cai C, Ma LQ (March 2015). "Novel precipitated zirconia-based DGT technique for high-resolution imaging of oxyanions in waters and sediments". Environmental Science & Technology. 49 (6): 3653–61. Bibcode:2015EnST...49.3653G. doi:10.1021/es505424m. PMID 25655234.

[13] Stockdale A, Davison W, Zhang H (April 2010). "2D simultaneous measurement of the oxyanions of P, V, As, Mo, Sb, W and U" (PDF). Journal of Environmental Monitoring. 12 (4): 981–4. doi:10.1039/b925627j. PMID 20383381.

[14] Pan Y, Guan DX, Zhao D, Luo J, Zhang H, Davison W, Ma LQ (December 2015). "Novel Speciation Method Based on Diffusive Gradients in Thin-Films for in Situ Measurement of Cr(VI) in Aquatic Systems". Environmental Science & Technology. 49 (24): 14267–73. Bibcode:2015EnST...4914267P. doi:10.1021/acs.est.5b03742. PMID 26535488.

[15] Chen CE, Zhang H, Jones KC (May 2012). "A novel passive water sampler for in situ sampling of antibiotics". Journal of Environmental Monitoring. 14 (6): 1523–30. doi:10.1039/c2em30091e. PMID 22538362.

[16] Zheng JL, Guan DX, Luo J, Zhang H, Davison W, Cui XY, et al. (January 2015). "Activated charcoal based diffusive gradients in thin films for in situ monitoring of bisphenols in waters". Analytical Chemistry. 87 (1): 801–7. doi:10.1021/ac503814j. PMID 25412473.

[17] Pouran HM, Martin FL, Zhang H (June 2014). "Measurement of ZnO nanoparticles using diffusive gradients in thin films: binding and diffusional characteristics". Analytical Chemistry. 86 (12): 5906–13. doi:10.1021/ac500730s. hdl:2436/621804. PMID 24831848.

[18] Lucas A, Rate A, Zhang H, Salmon SU, Radford N (August 2012). "Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters". Analytical Chemistry. 84 (16): 6994–7000. doi:10.1021/ac301003g. PMID 22812590.

[19] Chaplin J, Warwick P, Cundy A, Bochud F, Froidevaux P (25 August 2021). "Novel DGT Configurations for the Assessment of Bioavailable Plutonium, Americium, and Uranium in Marine and Freshwater Environments". Analytical Chemistry. 93 (35): 11937–11945. doi:10.1021/acs.analchem.1c01342. PMID 34432435. S2CID 237307309.

[20] Chaplin J, Christl M, Straub M, Bochud F, Froidevaux P (2 June 2022). "Passive Sampling Tool for Actinides in Spent Nuclear Fuel Pools". ACS Omega. 7 (23): 20053−20058. doi:10.1021/acsomega.2c01884. hdl:20.500.11850/554631. PMC 9202248. PMID 35722008. S2CID 249333570.

[21] "global-easysensor.com". Archived from the original on 2020-08-08.

[thomas-22] Thomas P (1 July 2009). "Metals pollution tracing in the sewerage network using the diffusive gradients in thin films technique". Water Science and Technology. 60 (1): 65–70. doi:10.2166/wst.2009.287. PMID 19587403.

[23] Zhang H, Davison W, Miller S, Tych W (1995-10-01). "In situ high resolution measurements of fluxes of Ni, Cu, Fe, and Mn and concentrations of Zn and Cd in porewaters by DGT". Geochimica et Cosmochimica Acta. 59 (20): 4181–4192. Bibcode:1995GeCoA..59.4181Z. doi:10.1016/0016-7037(95)00293-9. ISSN 0016-7037.

[24] Williams PN, Santner J, Larsen M, Lehto NJ, Oburger E, Wenzel W, et al. (2014-08-05). "Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice". Environmental Science & Technology. 48 (15): 8498–506. Bibcode:2014EnST...48.8498W. doi:10.1021/es501127k. PMC 4124062. PMID 24967508.

[25] Warnken KW, Zhang H, Davison W (June 2006). "Accuracy of the diffusive gradients in thin-films technique: diffusive boundary layer and effective sampling area considerations". Analytical Chemistry. 78 (11): 3780–7. doi:10.1021/ac060139d. PMID 16737237.

[26] Lucas AR, Reid N, Salmon SU, Rate AW (October 2014). "Quantitative assessment of the distribution of dissolved Au, As and Sb in groundwater using the diffusive gradients in thin films technique". Environmental Science & Technology. 48 (20): 12141–9. Bibcode:2014EnST...4812141L. doi:10.1021/es502468d. PMID 25252140.

[27] McGifford RW, Seen AJ, Haddad PR (March 2010). "Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films". Analytica Chimica Acta. 662 (1): 44–50. doi:10.1016/j.aca.2009.12.041. PMID 20152264.

[28] Davison W, Fones GR, Grime GW (June 1997). "Dissolved metals in surface sediment and a microbial mat at 100-μm resolution". Nature. 387 (6636): 885–888. Bibcode:1997Natur.387..885D. doi:10.1038/43147. S2CID 4261454.

[29] Warnken KW, Zhang H, Davison W (October 2004). "Analysis of polyacrylamide gels for trace metals using diffusive gradients in thin films and laser ablation inductively coupled plasma mass spectrometry". Analytical Chemistry. 76 (20): 6077–84. doi:10.1021/ac0400358. PMID 15481956.

[30] Williams PN, Santner J, Larsen M, Lehto NJ, Oburger E, Wenzel W, et al. (5 August 2014). "Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice". Environmental Science & Technology. 48 (15): 8498–506. Bibcode:2014EnST...48.8498W. doi:10.1021/es501127k. PMC 4124062. PMID 24967508.

[31] Hoefer C, Santner J, Puschenreiter M, Wenzel WW (April 2015). "Localized metal solubilization in the rhizosphere of Salix smithiana upon sulfur application". Environmental Science & Technology. 49 (7): 4522–9. Bibcode:2015EnST...49.4522H. doi:10.1021/es505758j. PMC 4394708. PMID 25782052.

[32] Davison W, Zhang H. Diffusion Layer Properties. In: Davison W, ed. Diffusive Gradients in Thin-Films for Environmental Measurements. Cambridge Environmental Chemistry Series. Cambridge University Press; 2016:32-65.

[33] Yabuki LN, Colaço CD, Menegário AA, Domingos RN, Kiang CH, Pascoaloto D (February 2014). "Evaluation of diffusive gradients in thin films technique (DGT) for measuring Al, Cd, Co, Cu, Mn, Ni, and Zn in Amazonian rivers". Environmental Monitoring and Assessment. 186 (2): 961–9. doi:10.1007/s10661-013-3430-x. PMID 24052239. S2CID 9781883.

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+{{Short description|Environmental chemistry technique}}
-{{User sandbox}}
+'''The diffusive gradients in thin films (DGT) technique''' is an [[environmental chemistry]] technique for the detection of [[Chemical element|elements]] and [[Chemical compound|compound]]s in aqueous [[Ecology#Physical environment|environments]], including [[Hydrosphere|natural waters]],<ref name="Chaudhary et al 2020">{{cite journal | vauthors = Chaudhary M, Quanz M, Williams J, Maltby E, Oakes K, Spooner I, Walker TR |title=Assessment of metal(loid) concentrations using Diffusive Gradient Thin (DGT) films in marine, freshwater and wetland aquatic ecosystems impacted by industrial effluents |journal=Case Studies in Chemical and Environmental Engineering |date=September 2020 |volume=2 |pages=100041 |doi=10.1016/j.cscee.2020.100041 |doi-access=free }}</ref> [[sediment]]s<ref name="Zhang et al 1998">{{cite journal | vauthors = Zhang H, Davison W, Gadi R, Kobayashi T |title=In situ measurement of dissolved phosphorus in natural waters using DGT |journal=Analytica Chimica Acta |date=August 1998 |volume=370 |issue=1 |pages=29–38 |doi=10.1016/S0003-2670(98)00250-5 }}</ref> and [[soils]].<ref name="pmid6353577">{{cite journal | vauthors = Wilkins CL | title = Hyphenated techniques for analysis of complex organic mixtures | journal = Science | volume = 222 | issue = 4621 | pages = 291–6 | date = October 1983 | pmid = 6353577 | doi = 10.1126/science.6353577 | bibcode = 1983Sci...222..291W }}</ref> It is well suited to ''in situ'' detection of [[bioavailable]] toxic [[trace metal]] contaminants.<ref name=inap>{{cite web|title=Diffusive Gradients in Thin-films (DGT): A Technique for Determining Bioavailable Metal Concentrations|url=http://www.inap.com.au/public_downloads/Research_Projects/Diffusive_Gradients_in_Thin-films.pdf|publisher=International Network for Acid Prevention|access-date=23 April 2015|date=March 2002|archive-date=28 February 2015|archive-url=https://web.archive.org/web/20150228234058/http://www.inap.com.au/public_downloads/Research_Projects/Diffusive_Gradients_in_Thin-films.pdf|url-status=dead}}</ref><ref>{{cite journal | vauthors = Strivens J, Hayman N, Johnston R, Rosen G | title = Effects of Dissolved Organic Carbon on Copper Toxicity to Embryos of Mytilus galloprovincialis as Measured by Diffusive Gradient in Thin Films | journal = Environmental Toxicology and Chemistry | volume = 38 | issue = 5 | pages = 1029–1034 | date = May 2019 | pmid = 30840314 | doi = 10.1002/etc.4404 | s2cid = 73466599 }}</ref><ref>{{cite journal | vauthors = Strivens J, Hayman N, Rosen G, Myers-Pigg A | title = Toward Validation of Toxicological Interpretation of Diffusive Gradients in Thin Films in Marine Waters Impacted by Copper | journal = Environmental Toxicology and Chemistry | volume = 39 | issue = 4 | pages = 873–881 | date = April 2020 | pmid = 32004383 | doi = 10.1002/etc.4673 | doi-access =  }}</ref> The technique involves using a specially-designed [[Environmental monitoring#Passive sampling|passive sampler]] that houses a binding [[gel]], [[Diffusion|diffusive]] gel and [[Membrane technology|membrane filter]]. The element or compound passes through the membrane filter and diffusive gel and is assimilated by the binding gel in a rate-controlled manner. Post-deployment analysis of the binding gel can be used to determine the time-weighted-average bulk solution [[concentration]] of the element or compound via a simple equation.
-<!-- EDIT BELOW THIS LINE -->
+[[File:DGT theory.png|thumb|right|300 px|According to DGT theory, the concentration of an analyte, [C],  tends toward 0 (μg/L, ng/L, etc.) as the analyte approaches the binding layer, passing through the diffusive boundary layer (DBL, ẟ) and the DGT device's diffusive gel (thickness of Δg). No reverse diffusion of the analyte back into the solution is assumed to occur.]]
-'''The diffusive gradients in thin films (DGT) technique''' is an [[analytical chemistry]] technique for the detection of [[elements]] and [[compounds]] in aqueous [[Environment|environments]], including [[Hydrosphere|natural waters]], [[Sediment|sediments]] and [[soils]].<ref name="pmid6353577">{{cite journal |doi=10.1038/367546a0| |title=In situ speciation measurements of trace components in natural waters using thin-film gels |year=1994 |last1=Zhang |first1=H. |last2=Davison|first2=D.|journal=Nature |volume=367 |issue=6463 |pages=546-8 }}</ref> The technique involves using a specially-designed [[Environmental_monitoring#Passive_sampling|passive sampler]] that houses a binding [[gel]], [[Diffusion|diffusive]] gel and [[Membrane technology|membrane filter]]. The element or compound passes through the membrane filter and diffusive gel and is assimilated by the binding gel in a rate-controlled manner. Post-deployment analysis of the binding gel can be used to determine the bulk solution [[concentration]] of the element or compound via a simple equation.
-[[File:DGT_Schematic.pdf|thumb|right|300 px|A schematic of the diffusive gradients in thin films sampler, showing the piston, binding gel, membrane filter and cap (outer sleeve).]]
-=History=
+==History==
+The DGT technique was developed in 1994 by Hao Zhang and William Davison at the [[Lancaster Environment Centre]] of [[Lancaster University]] in the [[United Kingdom]]. The technique was first used to detect [[Metals|metal]] [[cations]] in [[Ocean|marine]] environments using [[Chelex 100]] as the binding agent. Further characterisation of DGT, including the results of field deployments in the [[Menai Strait]] and the North [[Atlantic Ocean]], was published in 1995.<ref name="Zhang & Davison 1995">{{cite journal | vauthors = Zhang H, Davison W |title=Performance Characteristics of Diffusion Gradients in Thin Films for the in Situ Measurement of Trace Metals in Aqueous Solution |journal=Analytical Chemistry |date=October 1995 |volume=67 |issue=19 |pages=3391–3400 |doi=10.1021/ac00115a005 }}</ref> The technique was first tested in soils in 1998, with results demonstrating that kinetics of dissociation of labile species in the porewater (soil solution) could be determined via DGT.<ref>{{cite journal | vauthors = Harper MP, Davison W, Zhang H, Tych W |title=Kinetics of metal exchange between solids and solutions in sediments and soils interpreted from DGT measured fluxes |journal=Geochimica et Cosmochimica Acta |date=August 1998 |volume=62 |issue=16 |pages=2757–2770 |doi=10.1016/S0016-7037(98)00186-0 |bibcode=1998GeCoA..62.2757H }}</ref> Since then, the DGT technique has been modified and expanded to include a significant number of elements and compounds, including cationic metals,<ref name="Zhang & Davison 1995"/> nitrate,<ref name=":1">{{Cite journal|last1=Corbett|first1=Thomas D. W.|last2=Dougherty|first2=Hannah|last3=Maxwell|first3=Bryan|last4=Hartland|first4=Adam|last5=Henderson|first5=William|last6=Rys|first6=Gerald J.|last7=Schipper|first7=Louis A.|date=2020-05-20|title=Utility of 'Diffusive Gradients in Thin-Films' for the measurement of nitrate removal performance of denitrifying bioreactors|url=https://www.sciencedirect.com/science/article/pii/S0048969719352593|journal=Science of the Total Environment|language=en|volume=718|pages=135267|doi=10.1016/j.scitotenv.2019.135267|pmid=31859060 |s2cid=209425982 |issn=0048-9697}}</ref> [[phosphate]] and other [[oxyanion]]s ([[Vanadium|V]], [[Chromate and dichromate|Cr<sup>VI</sup>]], [[Arsenic|As]], [[Selenium|Se]], [[Molybdenum|Mo]], [[Antimony|Sb]], [[Tungsten|W]]),<ref name="Zhang et al 1998"/><ref>{{cite journal | vauthors = Santner J, Prohaska T, Luo J, Zhang H | title = Ferrihydrite containing gel for chemical imaging of labile phosphate species in sediments and soils using diffusive gradients in thin films | journal = Analytical Chemistry | volume = 82 | issue = 18 | pages = 7668–74 | date = September 2010 | pmid = 20735010 | pmc = 3432420 | doi = 10.1021/ac101450j }}</ref><ref>{{cite journal | vauthors = Luo J, Zhang H, Santner J, Davison W | title = Performance characteristics of diffusive gradients in thin films equipped with a binding gel layer containing precipitated ferrihydrite for measuring arsenic(V), selenium(VI), vanadium(V), and antimony(V) | journal = Analytical Chemistry | volume = 82 | issue = 21 | pages = 8903–9 | date = November 2010 | pmid = 20936784 | doi = 10.1021/ac101676w }}</ref><ref name=":0">{{cite journal | vauthors = Guan DX, Williams PN, Luo J, Zheng JL, Xu HC, Cai C, Ma LQ | title = Novel precipitated zirconia-based DGT technique for high-resolution imaging of oxyanions in waters and sediments | journal = Environmental Science & Technology | volume = 49 | issue = 6 | pages = 3653–61 | date = March 2015 | pmid = 25655234 | doi = 10.1021/es505424m | bibcode = 2015EnST...49.3653G }}</ref><ref>{{cite journal | vauthors = Stockdale A, Davison W, Zhang H | title = 2D simultaneous measurement of the oxyanions of P, V, As, Mo, Sb, W and U | journal = Journal of Environmental Monitoring | volume = 12 | issue = 4 | pages = 981–4 | date = April 2010 | pmid = 20383381 | doi = 10.1039/b925627j | url = https://eprints.lancs.ac.uk/id/eprint/31772/1/Stockdale_et_al_JEM_2010.pdf }}</ref><ref>{{cite journal | vauthors = Pan Y, Guan DX, Zhao D, Luo J, Zhang H, Davison W, Ma LQ | title = Novel Speciation Method Based on Diffusive Gradients in Thin-Films for in Situ Measurement of Cr(VI) in Aquatic Systems | journal = Environmental Science & Technology | volume = 49 | issue = 24 | pages = 14267–73 | date = December 2015 | pmid = 26535488 | doi = 10.1021/acs.est.5b03742 | bibcode = 2015EnST...4914267P }}</ref> [[antibiotics]],<ref>{{cite journal | vauthors = Chen CE, Zhang H, Jones KC | title = A novel passive water sampler for in situ sampling of antibiotics | journal = Journal of Environmental Monitoring | volume = 14 | issue = 6 | pages = 1523–30 | date = May 2012 | pmid = 22538362 | doi = 10.1039/c2em30091e }}</ref> [[bisphenol]]s,<ref>{{cite journal | vauthors = Zheng JL, Guan DX, Luo J, Zhang H, Davison W, Cui XY, Wang LH, Ma LQ | display-authors = 6 | title = Activated charcoal based diffusive gradients in thin films for in situ monitoring of bisphenols in waters | journal = Analytical Chemistry | volume = 87 | issue = 1 | pages = 801–7 | date = January 2015 | pmid = 25412473 | doi = 10.1021/ac503814j }}</ref> and [[nanoparticles]],<ref>{{cite journal | vauthors = Pouran HM, Martin FL, Zhang H | title = Measurement of ZnO nanoparticles using diffusive gradients in thin films: binding and diffusional characteristics | journal = Analytical Chemistry | volume = 86 | issue = 12 | pages = 5906–13 | date = June 2014 | pmid = 24831848 | doi = 10.1021/ac500730s | hdl = 2436/621804 | hdl-access = free }}</ref> and has even been modified for the [[Geochemistry|geochemical]] exploration of [[gold]].<ref>{{cite journal | vauthors = Lucas A, Rate A, Zhang H, Salmon SU, Radford N | title = Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters | journal = Analytical Chemistry | volume = 84 | issue = 16 | pages = 6994–7000 | date = August 2012 | pmid = 22812590 | doi = 10.1021/ac301003g }}</ref> DGT has also been developed and calibrated for the measure of [[radionuclides]], including for the analysis of [[actinides]] such as [[Uranium|U]], [[Plutonium|Pu]], [[Americium|Am]] and [[Curium|Cm]], both in the environment<ref>{{cite journal |vauthors = Chaplin J, Warwick P, Cundy A, Bochud F, Froidevaux P |title=Novel DGT Configurations for the Assessment of Bioavailable Plutonium, Americium, and Uranium in Marine and Freshwater Environments |journal=Analytical Chemistry |date=25 August 2021 |volume=93 |issue=35 |pages=11937–11945 |doi=10.1021/acs.analchem.1c01342 |pmid=34432435 |s2cid=237307309 |doi-access=free }}</ref> and even in cooling pools for spent nuclear fuel rods.<ref>{{cite journal |vauthors = Chaplin J, Christl M, Straub M, Bochud F, Froidevaux P |title=Passive Sampling Tool for Actinides in Spent Nuclear Fuel Pools |journal=ACS Omega |date=2 June 2022 |volume=7 |issue=23 |pages=20053−20058 |doi=10.1021/acsomega.2c01884 |pmid=35722008 |pmc=9202248 |hdl=20.500.11850/554631 |s2cid=249333570 |url=https://doi.org/10.1021/acsomega.2c01884|hdl-access=free }}</ref>
-The DGT technique was developed in 1994 by Hao Zhang and William Davison at [[Lancaster University]] in the [[United Kingdom]]. The technique was first used to detect [[Metals|metal]] [[cations]] in [[marine]] environments using [[Chelex 100]] as the binding agent. Further characterisation of DGT, including the results of field deployments in the [[Menai Strait]] and the North [[Atlantic Ocean]], was published in 1995.<ref>{{cite journal|doi=10.1021/ac00115a005|last=Zhang|first=H.|last2=Davison|first2=D.|title=Performance characteristics of diffusion gradients in thin films for the in situ measurement of trace metals in aqueous solution|journal=Analytical Chemistry|year=1995|volume=67|issue=19|pages=3391-3400}}</ref> The technique was first tested in soils in 1998, with results demonstrating that kinetics of dissociation of labile species in the porewater (soil solution) could be determined via DGT.<ref>{{cite journal|doi=10.1016/S0016-7037(98)00186-0| last1=Harper|first=M.|last2=Davison|first2=D.|last3=Zhang|first3=H.|last4=Wlodek|first4=W.|title=Kinetics of metal exchange between solids and solutions in sediments and soils interpreted from DGT measured fluxes|journal=Geochimica et Cosmochimica Acta|year=1998|volume=62|issue=16|pages=2757-2770}}</ref> Since then, the DGT technique has been modified and expanded to include a significant number of elements and compounds, including [[Phosphate|phosphorous]], [[antibiotics]], and [[nanoparticles]], and has even been modified for the [[Geochemistry|geochemical]] exploration of [[gold]].<ref>{{cite journal|doi=10.1021/ac301003g|last1=Lucas|first1=A.|last2=Rate|first2=A.|last3=Zhang|first3=H.|last4=Salmon|first4=U.|last5=Radford|first5=N.|title=Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters|journal=Analytical Chemistry|year=2012|volume=84|pages=6994-7000}}</ref>
+[https://www.dgtresearch.com/ DGT Research Ltd.] was established in July 1997 by the original developers of the technique, Profs. Davison and Zhang, and sells ready-made DGT® devices for water, soil and sediment deployments to measure different analytes, as well as the component parts for self-assembly. The company holds the original patents for the device and DGT® is a trademark which is registered throughout the world. In 2014 a rival company "[https://global-easysensor.com/product-category/diffusive-gradients-in-thin-film/ EasySensor]" was set up by Prof. Shiming Ding and supplies devices that the company claims are analogous to the original DGT® products.<ref>{{Cite web |date=|title=global-easysensor.com|url=https://global-easysensor.com/about/|url-status=live|archive-url=https://web.archive.org/web/20200808093526/http://global-easysensor.com:80/about/ |archive-date=2020-08-08 |access-date=|website=}}</ref>
-=The DGT device=
+==The DGT device==
-[[File:DGT_device.jpg|thumb|right|200 px|A photo of a disassembled DGT device, showing piston and cap. The device in this picture has been fitted with [[activated carbon]] for assimilating gold and/or [[Bisphenol|bisphenols]].]]
-The DGT device is made of plastic, and comprises a piston and a tight-fitting, circular cap with an opening (DGT window). A binding gel, diffusive gel and filter membrane (usually pre-cut into discs that are between 0.13-0.80 mm thick, although this can be varied) are stacked onto the piston, and the cap is placed over the assembly. The dimensions of the device normally ensure that the two gels and filter membrane are well-sealed when the cap is put on.
+[[File:DGT device.jpg|thumb|right|200 px|A photo of a disassembled DGT device, showing piston and cap. The device in this picture has been fitted with [[activated carbon]] for assimilating gold and/or [[bisphenol]]s.]]
+The most commonly used DGT device is a plastic "piston-type" probe, and comprises a cylindrical polycarbonate base and a tight-fitting, circular cap with an opening (DGT window). A binding gel, diffusive gel (typically a polyacrylamide hydrogel) and filter membrane are stacked onto the base, and the cap is used to seal the gel and filter layers inside<ref name="inap" />{{rp|4.2.3}} Dimensions of the gel layers vary depending on features of the environment, such as the flow rate of water being sampled;<ref name="inap" />{{rp|4.2.1}} an example is an approximately 2&nbsp;cm device diameter containing a 1mm gel layer.<ref name="thomas">{{cite journal | vauthors = Thomas P | title = Metals pollution tracing in the sewerage network using the diffusive gradients in thin films technique | journal = Water Science and Technology | volume = 60 | issue = 1 | pages = 65–70 | date = 1 July 2009 | pmid = 19587403 | doi = 10.2166/wst.2009.287 }}</ref> Other commonly used probe configurations include those for deploying in sediments (to measure solute mobilisation with depth)<ref>{{Cite journal| vauthors = Zhang H, Davison W, Miller S, Tych W |date=1995-10-01|title=In situ high resolution measurements of fluxes of Ni, Cu, Fe, and Mn and concentrations of Zn and Cd in porewaters by DGT |journal=Geochimica et Cosmochimica Acta|language=en|volume=59|issue=20|pages=4181–4192|doi=10.1016/0016-7037(95)00293-9|bibcode=1995GeCoA..59.4181Z|issn=0016-7037}}</ref> and in planar form for measuring solute dynamics in the plant rhizosphere.<ref>{{cite journal | vauthors = Williams PN, Santner J, Larsen M, Lehto NJ, Oburger E, Wenzel W, Glud RN, Davison W, Zhang H | display-authors = 6 | title = Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice | journal = Environmental Science & Technology | volume = 48 | issue = 15 | pages = 8498–506 | date = 2014-08-05 | pmid = 24967508 | pmc = 4124062 | doi = 10.1021/es501127k | bibcode = 2014EnST...48.8498W }}</ref>
 ==Principles of operation==
 ===Deployment===
-[[File:DGT_deployed_borehole.jpg|thumb|right|200 px|DGT devices being deployed into [[groundwater]] in the [[Tanami desert]], Australia.]]
+[[File:DGT deployed borehole.jpg|thumb|right|200 px|DGT devices being deployed into [[groundwater]] in the [[Tanami Desert]], Australia.]]
-DGT devices can be directly deployed in aqueous environmental media, including natural waters, sediments, and soils. In fast-flowing waters, the DGT face should be perpendicular to the direction of flow, in order to ensure the [[Boundary layer|diffusive boundary layer]] (DBL) is not increased by [[laminar flow]]. In slow-flowing or stagnant waters such as in ponds or [[groundwater]], deployment of DGT devices with different thicknesses of diffusive gel can allow for the determination of the DBL and a more accurate determination of bulk concentration.<ref>{{cite journal|doi=10.1021/ac060139d|last1=Warnken|first1=K.|last2=Zhang|first2=H.|last3=Davison|first3=W.|title=Accuracy of the diffusive gradients in thin-films technique:  diffusive boundary layer and effective sampling area considerations|journal=Analytical Chemistry|year=2006|volume=78|issue=11|pages=3780-3787}}</ref> Modifications to the diffusive gel (e.g. increasing or decreasing the thickness) can also be undertaken to ensure low detection limits.<ref>{{cite journal|doi=10.1021/es502468d|last1=Lucas|first1=A.|last4=Rate|first4=A.|last2=Reid|first2=N.|last3=Salmon|first3=U.|title=Quantitative Assessment of the Distribution of Dissolved Au, As and Sb in Groundwater Using the Diffusive Gradients in Thin Films Technique|journal=Environmental Science & Technology|year=2014|volume=48|issue=20|pages=12141-12149}}</ref>
+DGT devices can be directly deployed in aqueous environmental media, including natural waters, sediments, and soils.<ref name="Chaudhary et al 2020"/> In fast-flowing waters, the DGT device's face should be perpendicular to the direction of flow, in order to ensure the [[Boundary layer|diffusive boundary layer]] (DBL) is not affected by [[laminar flow]]. In slow-flowing or stagnant waters such as in ponds or [[groundwater]], deployment of DGT devices with different thicknesses of diffusive gel can allow for the determination of the DBL and a more accurate determination of bulk concentration.<ref name="inap" />{{rp|4.2.1}}<ref>{{cite journal | vauthors = Warnken KW, Zhang H, Davison W | title = Accuracy of the diffusive gradients in thin-films technique: diffusive boundary layer and effective sampling area considerations | journal = Analytical Chemistry | volume = 78 | issue = 11 | pages = 3780–7 | date = June 2006 | pmid = 16737237 | doi = 10.1021/ac060139d }}</ref><ref name=":1" /> Modifications to the diffusive gel (e.g. increasing or decreasing the thickness) can also be undertaken to ensure low detection limits.<ref>{{cite journal | vauthors = Lucas AR, Reid N, Salmon SU, Rate AW | title = Quantitative assessment of the distribution of dissolved Au, As and Sb in groundwater using the diffusive gradients in thin films technique | journal = Environmental Science & Technology | volume = 48 | issue = 20 | pages = 12141–9 | date = October 2014 | pmid = 25252140 | doi = 10.1021/es502468d | bibcode = 2014EnST...4812141L }}</ref>
-===Analysis of binding gels===
+===Analysis of binding gels and chemical imaging===
+After the DGT devices/probes have been retrieved, the binding gels can be eluted using methods that depend on the target analyte and the DGT binding gel (for example, [[nitric acid]] can be used to elute most metal cations from Chelex-100 gels).<ref name="inap" />{{rp|4.2.1}} NaOH can be used to elute most oxyanions from Zr-Oxide(Ding et al., 2010, 2011,2016; Sun et al.,2014).The eluent can then be quantitatively analysed via a range of analytical techniques, including but not limited to: [[ICP-MS]], [[Graphite furnace atomic absorption|GFAAS]]<ref name="inap" />{{rp|4.2.1}} [[ICP-OES]], [[Atomic absorption spectroscopy|AAS]],<ref name="thomas" /> [[Ultraviolet-visible spectroscopy|UV-Vis spectroscopy]] or computer imaging [[densitometry]].<ref>{{cite journal | vauthors = McGifford RW, Seen AJ, Haddad PR | title = Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films | journal = Analytica Chimica Acta | volume = 662 | issue = 1 | pages = 44–50 | date = March 2010 | pmid = 20152264 | doi = 10.1016/j.aca.2009.12.041 }}</ref> For chemical imaging and to obtain two-dimensional (2D) sub-mm high resolution distribution of analytes in heterogenous environments, such as [[sediment]]s and the [[rhizosphere]], the retrieved gel strips can be analyzed by [[Particle-induced X-ray emission|PIXE]] or LA-ICP-MS after gel drying.<ref name=":0"/><ref>{{cite journal | vauthors = Davison W, Fones GR, Grime GW |title=Dissolved metals in surface sediment and a microbial mat at 100-μm resolution |journal=Nature |date=June 1997 |volume=387 |issue=6636 |pages=885–888 |doi=10.1038/43147 |bibcode=1997Natur.387..885D |s2cid=4261454 |doi-access=free }}</ref><ref>{{cite journal | vauthors = Warnken KW, Zhang H, Davison W | title = Analysis of polyacrylamide gels for trace metals using diffusive gradients in thin films and laser ablation inductively coupled plasma mass spectrometry | journal = Analytical Chemistry | volume = 76 | issue = 20 | pages = 6077–84 | date = October 2004 | pmid = 15481956 | doi = 10.1021/ac0400358 }}</ref><ref>{{cite journal | vauthors = Williams PN, Santner J, Larsen M, Lehto NJ, Oburger E, Wenzel W, Glud RN, Davison W, Zhang H | display-authors = 6 | title = Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice | journal = Environmental Science & Technology | volume = 48 | issue = 15 | pages = 8498–506 | date = 5 August 2014 | pmid = 24967508 | pmc = 4124062 | doi = 10.1021/es501127k | bibcode = 2014EnST...48.8498W }}</ref><ref>{{cite journal | vauthors = Hoefer C, Santner J, Puschenreiter M, Wenzel WW | title = Localized metal solubilization in the rhizosphere of Salix smithiana upon sulfur application | journal = Environmental Science & Technology | volume = 49 | issue = 7 | pages = 4522–9 | date = April 2015 | pmid = 25782052 | pmc = 4394708 | doi = 10.1021/es505758j | bibcode = 2015EnST...49.4522H }}</ref>
-After the DGT devices have been retrieved, the binding gels can be eluted using methods that depend on the target analyte and the DGT binding gel (for example, 1 mol/L [[nitric acid]] can be used to elute most metal cations from Chelex-100 gels). The eluent can then be quantitatively analysed via a range of analytical techniques, including but not limited to: [[ICP-MS]], [[ICP-OES]], [[Atomic absorption spectroscopy|AAS]] or [[Ultraviolet-visible spectroscopy|UV-Vis spectroscopy]].
 ==The DGT equation==
-Once the mass of an analyte has been determined, the time-averaged concentration of the analyte, <math>C_{DGT}</math>, can be determined by application of the the following equation:
+DGT is based on the application of [[Fick's law]].<ref name="thomas" /> Once the mass of an analyte has been determined, the time-averaged concentration of the analyte in the bulk, <math>C_{DGT}</math>, can be determined by application of the following equation:
 :<math>C_{DGT} = \frac {M \Delta g}{DtA}\ </math>
+where <math>M</math> is the mass of the analyte on the resin, <math>\Delta g</math> is the combined thickness of the hydrogel layer and filter membrane (''i.e.'' the "diffusion layer"). The previously determined diffusion coefficient of the analyte ''in the type of diffusion layer used'' and at the ambient temperature is represented by ''<math>D</math>'' <ref>Davison W, Zhang H. Diffusion Layer Properties. In: Davison W, ed. ''Diffusive Gradients in Thin-Films for Environmental Measurements''. Cambridge Environmental Chemistry Series. Cambridge University Press; 2016:32-65.</ref>, <math>t</math> is the deployment time, and <math>A</math> is the area of the DGT window.<ref name="inap" />{{rp|Eq.2}} More elaborate analysis techniques may be required in cases where the [[ionic strength]] of the water is low and where significant [[Organic matter#Organic matter in water|organic matter]] is present.<ref>{{cite journal | vauthors = Yabuki LN, Colaço CD, Menegário AA, Domingos RN, Kiang CH, Pascoaloto D | title = Evaluation of diffusive gradients in thin films technique (DGT) for measuring Al, Cd, Co, Cu, Mn, Ni, and Zn in Amazonian rivers | journal = Environmental Monitoring and Assessment | volume = 186 | issue = 2 | pages = 961–9 | date = February 2014 | pmid = 24052239 | doi = 10.1007/s10661-013-3430-x | s2cid = 9781883 }}</ref>
-where <math>M</math> is the concentration of the analyte, <math>\Delta g</math> is the thickness of the diffusive layer and filter membrane together, <math>D</math> is the diffusion coefficient of the analyte, <math>t</math> is the deployment time, and <math>A</math> is the area of the DGT window.
-=See also=
+== See also ==
-{{Portal|Analytical chemistry}}
 * [[List of chemical analysis methods]]
 * [[Environmental monitoring]]
@@ Line 39: / Line 39: @@
 * [[Microanalysis]]
-=References=
+== References ==
-{{Reflist|1}}
+{{Reflist}}
-=External links=
+== External links ==
-http://www.dgtresearch.com
+* {{cite web |title=DGT Research |url=https://www.dgtresearch.com/ }}
+*[http://www.global-easysensor.com/ Global-EasySensor.com]
+[[Category:Environmental monitoring]]
-{{AFC submission|||ts=20141209072955|u=NZEnvScientist|ns=2}}