What are Water Isotope Probes?

Water Isotope Probes (WIPs) are used for direct, non-destructive in situ measurement of the stable water isotopes d18O and d2H. They work according to the "Diffusion Dillution Sampling" method (DDS, Volkmann and Weiler 2014) based on the equilibrium between gas and liquid phase (Direct Vapor Equilibrium method DVE).

In the DVE-DDS method, no absolute pressure gradient is established, but the equilibrium is set by diffusion, using the different water vapor partial pressure in the gas mixture in the filter cartridge and the surrounding medium (soil/ snow/ xylem/ air). This has the advantage that the WIPs can also be used under saturated conditions. However, the water inlet pressure of the filter cartridge used must not be exceeded, for example, due to a water overflow.

The probes were optimized by us on the basis of the well-founded scientific findings of Volkmann and Weiler (2014) (patent number DE102013013969B3) and are manufactured and distributed under exclusive license.

Structure and function of the WIPs

The WIPs consist of three parts: 1) the filter cartridge, 2) the shaft with mixing chamber, and 3) the protective tube that guides three gas transport capillaries in a defined geometry into the insertion shaft and into the filter cartridge.

The dilution capillary delivers dry air or N2 directly into the mixing chamber, allowing controlled dilution of the water content in the air, while the water outside the probe and the air in the filter cartridge can continue to exchange under equilibrium conditions.

The diluted air is constantly fed from the mixing chamber to the water isotope analyzer via the sampling capillary.

The flow capillary extends to the tip of the filter cartridge. It supplies additional dry air or N2 into the system and helps to compensate for negative pressure due to dilution rates less than the sampling rate of the water isotope analyzer. The flow-through capillary thus ensures that a partial pressure gradient is created rather than an absolute pressure gradient.

Optimum measuring success with our WIP system

You can also purchase the WIP probes individually. So far, we have only tested their optimal function in combination with our WIP system. To set up our WIP system, you will need, in addition to the WIPs:

• a WIP-Master with special software
• a Picarro water isotope analyzer with monitor and external pump
• a dry gas source
• if necessary, a distribution box (WIP hub) with connecting line

For the setup of a WIP system in our EcoLab flex we offer the WIP setup for EcoLabs.

Flyer WIPs