A frequently asked question is “how much sample is required for a surface area analysis?” The simple answer is that it depends: it depends on the type of instrument being used for the measurement, and its accepted measurement tolerance; it depends on the type of sample tube being used for the measurement, which affects the accepted measurement tolerance; it depends on the specific surface are of the sample, since this is the surface area per gram of sample; and it depends on the accuracy tolerance that is acceptable for the measurement, since the total surface under test will be compared to the accepted tolerance of the measurement. A description of these specifications follows.
A frequently asked question is “how much sample is required for a surface area analysis?” The simple answer is that it depends: it depends on the type of instrument being used for the measurement, and its accepted measurement tolerance; it depends on the type of sample tube being used for the measurement, which affects the accepted measurement tolerance; it depends on the specific surface are of the sample, since this is the surface area per gram of sample; and it depends on the accuracy tolerance that is acceptable for the measurement, since the total surface under test will be compared to the accepted tolerance of the measurement.
Generally Micromeritics physisorption analyzers can be grouped into 5 categories. These are ASAP single-port standard-pressure analyzers, with current models ASAP 2020 Plus and ASAP 2060; ASAP multiple-port analyzers and higher-pressure analyzers, with current models ASAP 2420 and ASAP 2460, and ASAP 2050; 3Flex 3500 analyzers; TriStar analyzers, with current models TriStar II 3020 and TriStar II Plus 3030; and Gemini, with current models Gemini VII 2390a, Gemini VI 2390p, and Gemini VII 2390t. Each of these groups of instruments has specified performance for blank tube analyses, when performed using specific sample tubes and analysis conditions. These performance specifications provide the maximum magnitude of the volume of gas adsorbed as a function of relative pressure for analysis of a sample tube containing no sample. For some, filler rods and isothermal jackets are required; and for some they are not. Some provide specifications for nitrogen analysis at 77K and argon at 87K, and some are for krypton analysis at 77K. For some cases, free space is measured; and for some free space is calculated from sample mass and density, and the measured free space of the empty sample tube.
A description of these specifications follows. Again, these are maximum acceptable deviations from zero volume adsorbed. Realize that most instruments operate at a level much greater than these specifications. In order to determine the performance of a particular instrument, perform a blank tube analysis on that instrument. Generally the analysis conditions for a blank tube analysis are loaded when the instrument application software is installed onto the computer controlling the instrument.
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