Saturation capacities typical values

The importance of a large dynamic range becomes obvious when taking into account measurements with strong background absorption as well as simultaneous measurements over a wide spectral region. From this point of view, CCD arrays are the most favored CS AAS detectors and were selected for the research spectrometers. Typical values for the saturation capacity between 600 000 and 800 000 electrons per pixel and a read-out noise of 5 to 30 electrons result in a shot-noise limited dynamic range of 600 to 800, which is quite sufficient for AAS applications. 

A selection of adsorption isotherms types (according to the lUPAC classification of physisorption isotherms) are schematically shown in Figure 1, where the adsorbed amount n is plotted against the relative pressure p/po of the adsorptive gas. Type I isotherms are typical for microporous materials, where the total pore volume of the adsorbent determines the saturation value. Reversible isotherms of type II are obtained for nonporous or macroporous materials, whereas type IV isotherms showing a hysteresis loop are characteristic of mesoporous materials, such as many practical catalytic materials. If the knee at point B of isotherm types II and IV is sufficiently sharp, the uptake at point B can be considered as the monolayer capacity of the material and its specific surface area can then be calculated assuming the formation of a close-packed monolayer of the test gas, provided its molecular area is known. For N2 the standard molecular area is 0.162 nm2. 

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