Respiration Chambers for Gas Flux Measurements & Isotope Labelling

• Chamber size and shape: The chamber should be large enough to provide sufficient headspace for gas exchange, but small enough to fit over the study area. Smaller chamber generally allow for faster detection of changing gas concentration in closed setups. The shape of the respiration chamber should be appropriate for the study system, whether it's a circular, square or rectangular shape for rhizoboxes, pots or vegetation plots in situ. An internal fan may help to homogenise the air within larger sized chamber (consider the limited pump speed of externally connected devices such as IRGAs). 
• Chamber materials: The chamber material should be as inert, non-reactive as possible and often transparent (for plant studies). Acrylic (PMMA) is a commonly used material for chambers. Other suitable materials are glass, polycarbonate or PET/PTFE (for measurements of reactive substances incl. volatiles). Consider the reduction of radiation (PAR) by any transparent material - and the consequences for photosynthetic assimilation. 
• Gas-tight seal: A gas-tight seal in closed chamber approaches is required to prevent loss or gain of gases from the chamber. Sealing can be achieved by the use of O-rings or gaskets and a clamp or screw system to hold the chamber in place. For field use, metal connection plates are often used at the bottom of the closed chambers, inserted a few centimetres into the ground. To avoid the build-up of overpressure, a pressure vent should be considered (this can be a tiny needle or a tube connected to a bottle of water).
• Gas sampling ports: Sampling ports allow the online measurement of gas concentrations within the chamber using common analysers, e.g. IRGA, Picarro, or the collection of gas alliquots in evacuated vials or sorbent tubes. The sampling ports on respiration chambers should be positioned at an appropriate position within the chamber and may be fitted with tubing for syringes, devices for automatic gas collection, or gas analyzers. Appropriate diffusers and spacing, together with internal mixing (particularly in larger chambers), will prevent inflow/outflow loops and inhomogeneous samples. Tubing on the inside of ports allows to position the air inlet and outlets at specific positions within larger chambers.
• Manipulation: Potentially insets of gas-tights gloves and airlocks (to enter tools or remove samples) can be useful to manipulate the chamber content, e.g. plants, while the respiration chamber is remaining closed. This is particular important when using the chambers for long term isotope labeling or to prevent insects (in combined insect-plant experimental cages) to escape. 
• Environment: Environmental variables such as temperature, humidity, pressure and light intensity can greatly affect organisms and thus gas flow measurements. A fully functional respiratory chamber should thus include sensors to monitor these variables, such as a temperature probe, humidity sensor and light sensor. In a closed chamber system operated over longer periods, monitoring of CO2 and O2 is required. Take appropriate measures to control environmental variables by placing chambers in growth rooms / regulate chamber temperature with cooling coils, scrubbing CO2 and/or water (Dryrite, Peltier elements, etc.) or use dedicated Gas Mixing or Control Systems. 

Overall, the construction of a gas flux / respiration chamber requires careful consideration of the materials used and environmental factors relevant in the study. Consultation with Vienna Scientific in cooperation with Qubit Systems can be helpful to ensure that the chamber design meets your specific research objectives.

• Select a chamber design: Different chamber designs are available depending on your research requirements. A typical design is a clear, airtight chamber that can hold a single plant or a group of plants. The chamber should have at least one inlet for introducing the labeled gas or solution and an outlet for removing excess gas. Other connections are beneficial.
• Monitor and control the environment: It is important to maintain or at least monitor the temperature, humidity and CO2 concentration within the chamber. This can be achieved by using sensors and controllers to regulate the environment. Vienna Scientific can assist you in sourcing the appropriate sensors, fans, scrubbers and/or provide a design that allows existing sensors to be installed in the new chamber.
• Build the labeling chamber: We will then construct the chamber using PMMA or polycarbonate. The chamber will be airtight to maintain the labeled environment, contain a positive pressure exhaust and all connectors needed to install sensors inside, water plants etc.
• Develop the gas mixer, tubing: If more than one gas cylinder is used to supply the isotopes, an appropriate mixer must be added before the air reaches the experimental isotope chamber. VSI will assist in the procurement of this chamber, flow meters, etc.

See above concerning further general recommendation for respiration chamber designs. Contact us to discuss possible isotope labeling chamber designs that meet your scientific objectives.