tube to prevent dust particles from traveling to the analyzers. use small amounts of cotton, say around 0.005 g, just enough to keep the dust out of the tubing. large amounts of cotton will block air flow when/if it gets damp. pour the drierite into the tube with a funnel, tap the tube on the bench to pack the grains tightly (to increase surface area – air + water rushes through loose drierite, requiring frequent changes of scrubbers), and cap off with a small amount of cotton. to remove carbon dioxide] before and after the animal chamber, ascarite ii is used (ascarite ii is a registered trademark of the arthur h. thomas co.). ascarite ii contains naoh, which is caustic (so don't get any on your skin and keep away from water). a scrubbing tube is prepared by placing a small amount of cotton into the tube end, filling one-third of the way with 10–20 mesh drierite, adding a small amount of cotton, then an additional third of the tube with the ascarite ii, another layer of cotton, followed by more drierite and capping the tube off with another small amount of cotton. tap the tube on the bench as each layer is added to pack the grains. note: driereite can be used over and over again (after heating in an oven), although indicating drierite will lose color with repeated drying; ascarite ii is used once and will be considered a hazardous waste. analyzers carbon dioxide analyzer: co2 analyzers typically use infrared-based detection methods to take advantage of the fact that co2 will absorb infra-red light and re-emit light at slightly longer wavelengths. the panel meter on the analyzer displays over the entire 0.01 – 10% co2 range and a voltage output proportional to co2 concentration is also generated for data recording. oxygen analyzer: oxygen analyzers suitable for respirometry use a variety of oxygen sensors, including galvanic ("ambient temperature"), paramagnetic, polarographic (clark-type electrodes), and zirconium ("high temperature") sensors. galvanic o2 analyzers use a fuel cell containing an acidic electrolyte, a heavy-metal anode and a thin gas-permeable membrane. since the partial pressure of o2 near the anode is zero, o2 is driven by diffusion to the anode via the membrane at a rate proportional to ambient o2 partial pressure. the fuel cell produces a voltage linearly proportional to the o2 partial pressure at the membrane. as long as cabinet temperature is stable, and provided that air flow across the fuel cell is stable and within range, the response will be 0.01% or better depending on supporting electronics, software, and other considerations. finally, a computer data acquisition and control system would be a typical addition to complete the system. instead of a chart recorder, continuous records of oxygen consumption and or carbon dioxide production are made with the assistance of an analog-to-digital converter coupled to a computer. software captures, filters, converts, and displays the signal as appropriate to the experimenter's needs. a variety of companies and individuals service the respirometry community (e.g., sable systems, qubit systems, see also warthog systems). mitochondrial metabolic rates inside the body oxygen is delivered to cells and in the cells to mitochondria, where it is consumed in the process generating most of the energy required by the organism. mitochondrial respirometry measures the consumption of oxygen by the mitochondria without involving an entire living animal and is the main tool to study mitochondrial function. three different types of samples may be subjected to such respirometric studies: isolated mitochondria (from cell cultures, animals or plants); permeabilized cells (from cell cultures); and permeabilized fibers or tissues (from animals). in the latter two cases the cellular membrane is made permeable by the addition of chemicals leaving selectively the mitochondrial membrane intact. therefore, chemicals that usually would not be able to cross the cell membrane can directly influence the mitochondria. by the permeabilization of the cellular membrane, the cell stops to exist as a living, defined organism, leaving only the mitochondria as still functional structures. unlike whole-animal respirometry, mitochondrial respirometry takes place in solution, i.e. the sample is suspended in a medium. today mitochondrial respirometry is mainly performed with a closed-chamber approach. closed-chamber system the sample suspended in a suitable medium is placed in a hermetically closed metabolic chamber. the mitochondria are brought into defined “states” by the sequential addition of substrates or inhibitors. since the mitochondria consume oxygen, the oxygen concentration drops. this change of oxygen concentration is recorded by an oxygen sensor in the chamber. from the rate of the oxygen decline (taking into account correction for oxygen diffusion) the respiratory rate of the mitochondria can be computed. basic research the functioning of mitochondria is studied in the field of bioenergetics. functional differences between mitochondria from different species are studied by respirometry as an aspect of comparative physiology. applied research mitochondrial respirometry is used to study mitochondrial functionality in mitochondrial diseases or diseases with a (suspected) strong link to mitochondria, e.g. diabetes mellitus type 2, obesity and cancer. other fields of application are e.g. sports science and the connection between mitochondrial function and aging. equipment the usual equipment includes a seal-able metabolic chamber, an oxygen sensor, and devices for data recording, stirring, thermostatisation and a way to introduce chemicals into the chamber. as described above for whole-animal respirometry the choice of materials is very important. plastic materials are not suitable for the chamber because of their oxygen storage capacity. when plastic materials are unavoidable (e.g. for o-rings, coatings of stirrers, or stoppers) polymers with a very low oxygen permeability (like pvdf as opposed to e.g. ptfe) may be used. remaining oxygen diffusion into or out of the chamber materials can be handled by correcting the measured oxygen fluxes for the instrumental oxygen background flux. the entire instrument comprising the mentioned components is often called an oxygraph. the companies providing equipment for whole-animal rspirometry mentioned above are usually not involved in mitochondrial respiromety. the community is serviced at widely varying levels of price and sophistication by companies like oroboros instruments, hansatech, respirometer systems & applications, ysi life sciences or strathkelvin instruments .