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HARDWARE INFORMATION

Total Organic Carbon Analyzer (TOCA)
Hardware Type
Processing Equipment, Water

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Description

The Total Organic Carbon Analyzer (TOCA) provides capabilities to measure total organic carbon, total inorganic carbon, total carbon, pH and conductivity in water. Samples are inserted into a sample access door using a water sample syringe. The analysis takes place automatically within the analyzer with the push of a button on the instrument's front panel.  

After a sample syringe is inserted, the sample inlet system pumps water into the analyzer for analysis. Conductivity and pH are first measured using flow-through sensors with automatic temperature compensation. Phosphoric acid (6M solution) is added to the sample to convert inorganic carbon to carbon dioxide (CO²) gas. The acidified sample enters a transfer module where CO² gas passes through a selective membrane into a deionized water stream. The conductivity of the deionized water is then measured and converted to a value for total inorganic carbon.

After total inorganic carbon measurement, the sample stream is either routed through or around the inorganic carbon removal (ICR) module. This module is used to remove high levels of total inorganic carbon from water samples. If a sample contains much higher levels of total inorganic carbon than total organic carbon, accuracy can be improved by removing the total inorganic carbon prior to measurement of total organic carbon. Ammonium persulfate (15% weight by volume) is added to the sample downstream of the ICR module. The sample then enters the oxidation reactor where ultraviolet light converts organic carbon to CO² gas. The stream flows from the reactor into a second transfer module where the CO² gas passes through a membrane into the deionized water stream. The conductivity of the deionized water is subsequently measured and converted to either total carbon (with ICR module bypassed) or total organic carbon (when ICR module is used).

Sample waste is collected in the waste collection system. The waste bag contains sodium bicarbonate to instantly neutralize the waste stream as it enters the bag. The total weight of the flight unit is 23.6 kg.

Versions of this Hardware
+ As Configured for the NASA-Mir Missions
+ As Configured for the STS-71, Mir 18, Mir 19 and Mir 20 Missions
+ Version Used During the International Space Station (ISS) Experiments
+ Version Used During Ground-based Experiments