How does the PAT700 avoid measurement interference from TIC?
The PAT700 measures both TIC and TC using a single sensor, thus avoiding interference from TIC.
Most modern water systems use reverse osmosis (RO) as part of their water generation system. RO systems tend to concentrate the levels of CO2 present in the water loop as they RO membranes are permeable to CO2, but a percentage of the water is rejected. Thus the same amount of CO2 is present, but the quantity of water is reduced, hence increasing the concentration of CO2 in the water. In pharmaceutical quality water systems, the TIC is largely made up from dissolved CO2 present in the water. This increase in CO2 concentration typically leads to TIC levels in the ppm range, whereas TOC levels in a modern water system are frequently in the low ppb range. Hence TC is also in the ppm range too as TC = TIC + TC. If the TOC analyzer uses two separate sensors to measure TIC and TC, then slight drift between the two sensors can mean that the TOC analyzer will either over-report the TOC level, under-report the TOC level, or even report negative TOC levels. By using just one sensor to measure both TIC and then oxidizes the TOC to measure TC using the same sensor, the PAT700 avoids interference in the measurement from TIC.