Sample Measurement System is Setup and Ready for Analysis

Our research lab is equipped with a custom measurement system, specifically designed for the measurement of dissolved inorganic carbon (DIC) content in aqueous solution. The instrument was originally developed by Phil Bresnahan, working with Dr. Todd Martz at Scripps Institution of Oceanography in San Diego. The device takes in an aqueous sample and the mixes it with a select acid (in this case H3PO4) to push the pH in the reaction vessel to 4. This push the mole fraction of CO2 to one so that there is no longer any carbonate or bicarbonate ions left in solution. If the mole fraction of CO2 is one the partial pressure of CO2 in solution drastically increases and effectively all of the CO2 will degas out of solution. An inert carrier gas is ran into the reaction vessel carrying the now gaseous CO2 through a series of drying tubes to remove any moisture before the fluid enter a Li-COR 7000. The Li-COR 7000 is a multifunctional instrument, but as setup in this system it measure the partial pressure of CO2 and the ppm of CO2 in the gaseous sample. The ppm measure of CO2 is the converted back in to a micro-molarity and used for comparison to other samples.

(1) Sample volume to be injected into reaction chamber via mechanical syringe. (2) Sample is acidified with H3PO4, converting the dissolved carbonate and bicarbonate ions back into CO2. (3) Carrier gas, N2, moves CO2 (g) generated from sample through a semipermeable drying tubing to remove moisture. (4) Sample is then ran through a LI-COR-7000 and CO2 concentration is measured via non-dispersive infrared gas analysis. (5) The LabVIEW environment developed for this instrument system converts DIC values (ppm) to 𝜇mol/L.

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