When searching for an indicating gas purifier, you will find there are many filters containing a variety of moisture indicators on the market. It is important that you pick the right indicator for your specific application to get optimal performance. The moisture indicators change color at various water vapor concentrations. To decide which type of indicator you need, first determine the highest amount of water vapor your system can handle. Once determined, you can pick the right moisture indicator based on the water vapor concentration the indicators begin to change colors at.
Below are the main types of indicators you will find in the industry:
High Sensitivity Moisture Indicator: The most sensitive moisture indicator on the market. A unique manganese-based moisture indicator that changes color from blue to brown at moisture exposure of 1 ppm. It is Cobalt free and should be used with all of your critical analyses.
CuCl2/Silica Gel Indicator: A PH-sensitive dye on silica gel that contains no Cobalt. The indicators are able to show moisture from gross leaks in systems that introduce large amounts of water. The color change is yellow to blue-green, and will begin to change color with exposure to 4-6% Relative Humidity.
Gel Silica Indicators: Another Cobalt free, gel silica indicator that changes color from yellow to clear when exposed to high levels of water vapor. We have seen a lot of variation of these type of indicators, from 5% relative humidity to no effective color change at any humidity.
Indicating Drierite: This indicator contains Cobalt, which is listed as a “Substance of High Concern” in Europe. Many organizations are choosing to move toward a Cobalt Free Indicator like the CuCl2/Silica Gel Indicator instead of the Indicating Drierite in order to stay in compliance in the EU. The indicating Drierite will change color from blue to pink with exposure to 5% Relative Humidity.
Guidance on Cobalt Use: A good reference to the requirements for cobalt use under REACH in the EU can be found at this link: Cobalt Reach Consortium . However, the question as to whether the use of cobalt dichloride as an indicator has been definitively banned has been the subject of some argument in the industry, with some stakeholders arguing that alternative materials are not required. At a high level, it appears that guidance from the ECHA (European Chemicals Agency) has been (1) the CoCl2 is a substance of high concern, and (2) substitutes should be pursued where possible. A good background document related to this guidance can be found at ECHA Background document for cobalt dichloride .
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