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Welcome to AEL/LEA New Caledonia

Thoe old

Automatic sampler using passive DGT®
devices for water analysis : technical features

THOË® is a patented automatic and autonomous sampler using DGT® devices for the analysis of both dissolved metals and organic compounds in seawaters and freshwaters. Fully programmable, THOË® makes it possible to provide on a monitoring site concentrations time series recorded over several months.


  • 30 metals including
    Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn;
  • Phosphorus and oxyanions including
    As, Mo, Sb, Se, U, V, W;
  • Phosphates and more than 40 metals including
    Al, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Sb, Se, U, V, W, Zn;
  • Hg and As (III);
  • Cr(VI);
  • Polar organic compounds including antibiotics;
  • Polar organic compounds including pesticides
    and certain pharmaceutical products.
DGT® is a simple commercially available device for measuring inorganic/organic pollutants, nutrients and other dissolved components in water.


  • Possibility of exposing 12 DGT® sequentially;
  • Programming time sequences from few hours to several weeks;
  • Built-in temperature sensor for accurate concentration calculation;
  • Titanium rotation axis to direct the DGT® towards the current;
  • Maximum immersion depth of 1000 m;
  • Structure, carrousel and seals in chemically inert components (PEEK, PETP, PTFE and Silicon);
  • Autonomy in immersion mode of more than one year;
  • Multiple deployment options available.

Automatic sampler using passive DGT® devices for water analysis: analytical performance

A new analytical methodology for water emerges with the development of DGT® technology coupled with the THOË® automatic sampler developed by AEL/LEA and built by TECHNICAP.

For example, for many years environmental monitoring of the marine environment has been conducted on the basis of spot sampling of water. This type of strategy generates significant logistical costs and makes the acceptance of high frequency sampling difficult.

The performances of this new methodology have been compared to the spot sampling of waters for dissolved metal pollutants. In the example of monitoring the port of Nouméa (New Caledonia), the results underline the remarkable similarity of the concentrations between the three different methodologies, but with the advantage for THOË to obtain time series without the typical logistical constraints.

Example for seawater: 3 methods for the analysis of dissolved metals

Passive sampling with DGT® devices coupled with an automatic sampler THOË® and ICP-MS analysis
Spot sampling, off-line preconcentration and ICP-OES analysis (Moreton, et al, 2009)
Spot sampling, on-line preconcentration and ICP-MS analysis
Sampling protocol
Triplicate DGT® devices sequentially exposed for 3 days each over a 9 day period
9 spot samples collected in triplicate over a 9 day period
9 spot samples collected in triplicate over a 9 day period
Sample treatment
Chelex® binding layer (iminodiacetate) Elution in 4 mL of 1M HNO3 solution
250 x preconcentration using Dionex® OnGuard II M 1cc (iminodiacetate) cartridges and elution with 2M HNO3 solution
10 x preconcentration on Chelex® (iminodiacetate) column and elution with 1M HNO3 solution
Analytical instrumentation
Perkin Elmer
NexION® 350 ICP-MS
Varian® 730 ICP-OES
Perkin Elmer
NexION® 350 ICP-MS + seaFAST®

Results for dissolved Ni etPb

The similarities are particularly high for Ni and in good agreement for Pb. Concentration variations observed with spot sampling over time are generated by the daily influence tidal movements, whereas concentrations determined by DGT® correspond to average concentrations calculated over the exposure period (3 days).

Today, THOË® automatic samplers are deployed routinely to determine dissolved metal concentrations in marine and continental environments.

Automatic sampler using passive DGT® devices for water analysis: field applications

THOË® is a versatile sampler that can operate in both marine and freshwater environments for a wide range of monitoring/studies applications. Indeed, the use of the DGT® technology combined with sequential automatic sampling makes it possible to acquire time series of mean concentrations over several months.

Application areas:

  • Baseline surveys, impact studies, risk assessment of aquatic environments;
  • Regulatory monitoring, including the marine environment, ports, estuaries, rivers and lakes or reservoirs;
  • Scientific programs in the field of the transfer of chemicals in waters…

Dissolved Copper concentrations from a marina (above):
Each DGT® was exposed during three days over a one month deployment period. Concentration variations observed over time result of the influence tidal cycles.

Dissolved nickel concentrations determined for two monitoring sites at increasing distances from a marine outfall of mining effluents (left):
Each DGT® was exposed for a week during a two month deployment period. The temporal variations reflect the pollutant load changes at 30 and 1000 m distance.

THOË® is designed to be submerged up
to a depth of 1000 m.. It can be fixed on a
mooring line, placed on the bottom using feet
attachments (optional legs) or deployed
on the surface of the water (optional float).