Absorption bases

Figure 8-60 presents actual total heats of absorption based on experimental studies [32]. As long as the hydrocarbon absorption is in the range of 80-120°F, the values read from the graph should apply. 

Experiments with rats given oral doses of tritiated food-grade mineral oil provide supporting evidence that the absorption of hydrocarbons in mineral oils is limited. Five hours after dosing with 0.66 mL/kg of tritiated mineral oil ("liquid petrolatum U.S.P."), -75% of the administered radioactivity remained in the alimentary tract, and only 3% of the administered radioactivity was accounted for by radioactivity in other parts of the rat carcass (Ebert et al. 1966). About 80% of the administered radioactivity was recovered in feces during the first 2 days after treatment, and over 90% of the radioactivity in the feces was in the form of mineral oil. These data are consistent with the hypothesis that ingested mineral oil was poorly absorbed. Neither biliary excretion nor enterohepatic circulation of mineral oils was measured in this study, and thus, any quantitative estimates of the extent of absorption based on these data should be viewed as tentative. 

Creams are semisolid emulsion systems having a creamy appearance as the result of reflection of light from their emulsified phases. This contrasts them with simple ointments, which are translucent. Little agreement exists among professionals as to what constitutes a cream, and thus the term has been applied both to absorption bases containing emulsified water (w/o emulsions) and to semisolid o/w systems, which are physicochemically totally different, strictly because of their similar creamy appearances. Logically, classification of these systems should be based on their physical natures, in which case absorption bases would be ointments and the term cream could be reserved exclusively for semisolid o/w systems, which in all instances derive their structures from their emulsifiers and internal phases. 

Kaiampokis, A., Argyrakis, P., Macheras, P., A heterogeneous tube model of intestinal drug absorption based on probabilistic concepts, Pharm. Res. 1999, 16, 1764-1769. 

Fig. 19.7. Correlation between predicted oral absorption based on polar surface area (PSA) and in vivo oral bioavailability for a series of beta-blockers. The nonlinearity is related to the different levels of P-gp efflux and differences in CYP3A4 metabolism of these compounds [25],...

Baldini / Scheggi 1992 absorption-based fiber sensor (cobalt dye)... 

Figure 3. A typical configuration for absorption-based optical sensing.

Figure 4. A planar, evanescent-wave absorption-based sensor platform.

The absorption-based platforms described previously employed evanescent wave interrogation of a thin sensing layer coated onto a planar waveguide. A sensitivity enhancement strategy for optical absorption-based sensors based on planar, multimode waveguides was developed recently by us18. The objective was to apply this theory to the development of low-cost, robust and potentially mass-producible sensor platforms and the following section outlines the assumptions and predictions of this theoretical model. 

Figure 6 illustrates the platform under consideration in this analysis. The principle of sensor operation is as described previously for absorption-based optical sensors employing evanescent wave interrogation of the sensing layer. 

Figure 6. Optical absorption-based sensor platform under consideration for enhancement strategy.

While planar optical sensors exist in various forms, the focus of this chapter has been on planar waveguide-based platforms that employ evanescent wave effects as the basis for sensing. The advantages of evanescent wave interrogation of thin film optical sensors have been discussed for both optical absorption and fluorescence-based sensors. These include the ability to increase device sensitivity without adversely affecting response time in the case of absorption-based platforms and the surface-specific excitation of fluorescence for optical biosensors, the latter being made possible by the tuneable nature of the evanescent field penetration depth. 

Polerecky L., Burke C.S., MacCraith B.D., Optimization of absorption-based optical chemical sensors that employ a single-reflection configuration, Appl. Opt. 2002 41 2879-2887. 

Optical absorption-based correlation spectroscopy is a means of selectively detecting, or "fingerprinting", gases, in this work, of industrial importance. Optical correlation spectroscopy methods of gas detection are... 

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