Pressurized detection, or static read, is a technique used for concentrating the CO2 produced by the oxidation of the sample. The technique can be used for both qualitative and quantitative analysis. In this section the basics of the pressurization technique will be described.
Using the traditional use of NDIR technology, these measurements are performed by oxidation of the specific carbon component by UV/Persulfate oxidation to create CO2, which is swept through an NDIR detector. In this technique, the adsorption of the infrared light is measured over time as the CO2 is swept through the detector. The resulting measurement correlates to a peak, which can be integrated and correlated to a concentration.
The use of a pressurized detection scheme, or static read, allows for the specific carbon component to be oxidized and the resultant carbon dioxide swept into the detector using a non-interfering, inert gas, which is metered by a mass flow controller. A valve located at the outlet of the detector prevents the escape of any of the CO2 from the detector. A single measurement can be made to determine the amount of CO2 in the detector cell. The reading correlates directly to the concentration of the carbon contribution from the sample.
An inherent advantage of this technique is that all of the CO2 is in the cell at the same time for the detector measurement. With all of the CO2 in the cell, the sensitivity of the analysis is significantly increased.
Another advantage of this application is that there is one measurement made that represents the concentration of CO2 in the cell versus multiple measurements made in flow-through designs over time that result in a peak. Since this technique is a static read, it eliminates the inherent error that is associated with time delays between measurements with traditional flow-through technology. These time delays add error to the integration of the CO2 peak. The elimination of this error allows for lower detection limits and increased precision.
The static read of the detector is accomplished by pressurizing the detector cell with carrier gas, which contains the CO2 from the oxidized sample. The pressure required for static read is generally between 30-60psig. Tekmar’s recommended pressurization setting is 50psig.