Layered sorbents

Precoated layers sorbents with wide range of sorption properties for selectivity optimisation (HPTLC)... 

Raisglid and Burke (1997) recently reported on the concept of layering sorbents for effective SPE. One example included layering an amino sorbent... 

A second example is the layering of C-2 over C-18 for sorbing a mixture of hydrophobic and moderately hydrophobic pesticides. The concept is that the most hydrophobic pesticides sorb to the C-2 and are quantitatively eluted. While the more polar pesticides pass through the C-2 and sorb on the C-18. The concept of layering sorbents is an interesting approach that could be exploited for other applications of SPE. 

RGURE 12.18 Drying curves fr>r freeze-drying in layered sorbent—material configurations 1 —sublimation from free material surface 2—two-layer structure of material-sorbent 3—three-layer structure of sorbent—material—sorbent 4—multilayer structure. (From Tutova, 1988.)... 

Theoretically any metal oxide could be used as a thin-layer sorbent, but most have no specific properties that promote a unique separation or selectivity to a thin-layer plate. Infrequently, someone publishes work done on another metal oxide, but only those mentioned above are used frequently and are considered significant. 

Quenching effects of solvents, layer sorbents, and sample constituents are taken into account by modem LSC instmments. Samples with low levels of radioactivity are counted for a longer period and background correction is performed using a blank layer section taken from an area adjacent to the zone of radiolabeled compound. 

The model of TLC layer used in our calculations is shown in Figure 1. The TLC layer (sorbent) consisted of many parallel sublayers whose thickness equaled the mean particle diameter. The total reflectance, R, and transmittance, T, were obtained by summing all transmitted and reflected fractions of all sublayers. 

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