Absorbance gradient

FIGURE 7 The absorbance gradient trace used to measure the system dwell volume of a Waters Alliance system. Inset shows the intersection point marking the gradient onset. 

For heterogeneous samples this gradient does not become obvious in the imaging data. This is demonstrated in Figure 9.10, which shows a separahon of the water and oil phases in an oil-in-water emulsion. Here, the absorbance gradient cannot be detected due to the large heterogeneity of the component distribution. 

Figure 9.9 ATR FT-IR images of the distribution of a release coat (PVSC) on the PP-backing of an adhesive tape. Sample 1 ( bad ) has a heterogeneous (a) and sample 2 ( good ) a homogeneous (d) distribution of the release coat. The absorbance gradient observed for the original PP-backing is demonstrated in panels (b), (c), (e) and (f). Reproduced with permission from Ref [38] 2006, Society for Applied Spectroscopy.

Usually, the absorbance measurements are taken in the maximum of the spectrum (peak for example) due to several reasons. On one hand, the maximum sensitivity (greater slope in the calibration curve) is obtained at this wavelength. On the other hand, the centre of the maximum is where the absorbance gradient is minimum vs. the wavelength, which means lower probability of deviations from the Beer-Lambert law due to the polychromatism of the selected radiation. Finally, it will be a lesser variation of the method sensitivity due to the imprecision in positioning the wavelength. Measurements are sometimes performed not at the maximum, but in other places (shoulder, for... 

Calcium is absorbed from the intestine by facilitated diffusion and active transport. In the former, Ca " moves from the mucosal to the serosal compartments along a concentration gradient. The active transport system requires a cation pump. In both processes, a calcium-binding protein (CaBP) is thought to be required for the transport. Synthesis of CaBP is activated by 1,25-DHCC. In the active transport, release of Ca " from the mucosal cell into... 

Outside air entering the space through openings near the ground spreads over the floor and absorbs energy from the floor surface. The resulting air temperature increase leads to buoyancy and forces the air up into the upper hall zone. This results in a temperature stratification in the hall. Due to this vertical temperature gradient, the air in the occupied zone does not reach the exhaust air temperature (see Fig. 11.37). 

Figure 3 Reversed-phase chromatography of products after alkaline hydrolysis of /3-poly(L-malate), Discrete polymer products are formed, which differ in length by several units of L-malate. The absorbance at 220-nm wavelength was measured, (a) /3-Poly(L-malate) before hydrolysis, (b) After 10-min incubation in 20 mM NaOH at 37°C. (c) After 15 h in 20 mM NaOH at 37°C. (d) After I h in 500 mM NaOH at 100°C. High pressure chromatography (HPLC) on Waters reversed-phase Ci8- i-Bondapak. The methanol gradient (in water-trifluoro acetic acid, pH 3.0) was programmed as follows 0-40 min 0.3-23%, 40-47 min 23-40%, 47-49 min 40%, 49-54 min 40-0%. (d) Inset size exclusion chromatography after 3-min alkaline hydrolysis at pH 10.2. BioSil SEC 250 column of 300 mm x 7.8 mm size, 0.2 M potassium phosphate buffer pH 7.0.

A solar pond does not concentrate solar radiation, hut collects solar energy in the pond s water by absorbing both the direct and diffuse components of sunlight. Solar ponds contain salt in high concentrations near the bottom, with decreasing concentrations closer to the surface. This variation in concentration, known as a salt-density gradient, suppresses the natural tendency of hot water to rise, thus... 

In connection with the thermodynamic state of water in SAH, it is appropriate to consider one more question, i.e., their ability to accumulate water vapor contained in the atmosphere and in the space of soil pores. It is clear that this possibility is determined by the chemical potential balance of water in the gel and in the gaseous phase. In particular, in the case of saturated water vapor, the equilibrium swelling degree of SAH in contact with vapor should be the same as that of the gel immersed in water. However, even at a relative humidity of 99%, which corresponds to pF 4.13, SAH practically do not swell (w 3-3.5 g g1). In any case, the absorbed water will be unavailable for plants. Therefore, the only real possibility for SAH to absorb water is its preliminary condensation which can be attained through the presence of temperature gradients. 

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