GLC determination of guaiacol glyceryl ether in blood.

it was difficult to obtain directly in a single experiment films of exactly 0.1-mm. thickness, several films were selected so that the thickness of each film might be distributed in a range from 0.05 to 0.4 mm. and the respective water vapor permeability was measured at various humidity conditions. Plotting the relationship between permeation resistance (l/Q) and film thickness (I) gave a straight line. Thus, the permeability (Q) of the film of a given thickness (I) in various conditions could be obtained. Figure 1 suggests some noteworthy points. According to Eq. 2, the relationship between Q (=q/A) and Ap (=PI-p2) should be linear and proportional. As shown in Fig. 1, however, most of the obtained curves do not agree with Eq. 2. In particular, the value of Q for PVA does not increase after the maximum point, even when the value of Ap increases. The cause of this apparently controversial phenomenon may be that the permeability, Q, depends not only on the pressure difference between the higher vapor pressure side and the lower side, but also on the mean humidity condition to which the test film is subjected. This feature may be called the water vapor pressure dependency of permeability. The permeability coefficient (P) for a hydrophobic film is constant, because water vapor does not interact with the film, and the experimental data correspond to m. 1 or 2. On the other hand, for hydrophilic films such as coating films, the value of P changes according to the humidity condition, because water vapor interacts with the film; thus Eq. 1 or 2 does not apply to the hydrophilic film. The relationship between Pand Ap was obtained from Eq. 2 by using the data of Fig. 1. Figure 2 shows the results obtained. The value of P changed sharply, especially for the PVA film. Figure 3 illustrates the relationship between Q and Ap for the double-layer film, which has the remarkable two-sided feature of permeation. For comparison, this figure also shows the curves obtained with each single-component film. The permeability Q of the single films and of the double-layer film is expressed on the basis of 0.1-mm. thickness. It was found (Fig. 3) that twwsided features, classified as Group (Y and Group 6 (l), occurred over different humidity ranges. These features will, of course, change according to the sort of double-layer film or the combination of single films used therein. SUMMARY …