Gradients, measurement absorbance

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. 

A method for determining the alteration of the refractive index of a medium as a result of the temperature rise in the path of a beam of coherent light absorbed by the medium. Thermal lensing can also occur with pigmented proteins, and this phenomenon can influence the accuracy of concentration gradient measurements in small aperture flow cuvettes as well as in ultracentrifugation. 

Figure 5. Size analysis of Inhibitors I and 11 specific mRNA from levels of 9- and 18-h singly wounded tomato plants and 18-h doubly wounded plants. Poly(A ) RNA was applied to 15-30% linear sucrose gradients and was spun at 25,000 rpm. Twenty-five fractions were collected, the absorbency was measured, and the mRNA was precipitated by cold ethanol. In vitro translations were performed with each fraction in a rabbit reticulocyte system, and isolation of the preinhibitors with preformed antibody precipitates located the position of the two inhibitors. The gradients were calibrated by centrifugation of tomato leaf polyfA)" RNA on an identical gradient. The locations of translatable mRNAs for Inhibitors I and II were identical with RNA obtained from 9- and 18-h singly wounded or 18-h doubly...

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... 

Most polymers and FRPs absorb moisture and are therefore hygroscopic in nature. In general, the moisture absorption process in a polymer has been modeled using Pick s law. Pick s law states that the rate of transfer of a diffusing substance through unit area of a section is proportional to the concentration gradient measured normal to the section, that is. 

If the diffusion coefficient and 5t of the absorbed liquid are known, the echo experiment can provide information on the grain and pore characteristics. The backgroimd field gradient calculated from the observed local magnetic field distribution and the known grain dimensions is compsired with the effective gradient measured by the spin echo experiment (asstuning the self-diffusion coefficient of the liquid is that of the bulk liquid) in table 2. 

Fig. 2. Sedimentation analysis of RNA extracted from immature erythrocytes of an anemic duck after in vitro labeling with uiidine- H. Cells were incubated with tritiated uridine. Sedimentation was carried out in 5-20% (w/v) sucrose gradients in acetate buffer, 0-0.1 M, pH 5, at 25,000 rpm and 0 C for 9.5 hours. Ultraviolet absorbancy was measured, TCA-precipitable material was collected on Whatman GF/B glass fiber disks, and radioactivity was counted as described, (a-d) 30, 60, 90, and 270 minutes incubation, respectively, (e) 30 minutes labeled followed by 30 minutes in presence of actinomycin at 20 /tg/ml (curve x) 60 minutes preincubation with actinomycin followed by 30 minutes labeling (curve y). (f) Specific activity of total RNA (x) control, (y) actinomycin added at 30 minutes. From Scherrer et al. (1966).

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.

ESR spectroscopy can be transformed into an imaging method, ESRI, for samples containing unpaired electron spins, if the spectra are measured in the presence of magnetic field gradients. In an ESRI experiment the microwave power is absorbed by the unpaired electrons located at point x when the resonance condition, Equation (10), is fulfilled. 

Nafion absorbs MeOH more selectively than water, and the MeOH diffusion flow is higher than the osmotic water flow in Nafion membranes. Diffusion coefficients of Nafion 117 determined by different techniques have been reported. Ren et al. measured MeOH diffusion coefficients in Nafion 117 membranes exposed to 1.0 M MeOH solutions using pulsed field gradient (PPG) NMR techniques. The MeOH self-diffusion coefficient was 6 x 10 cm S and roughly independent of concentration over the range of 0.5-8.0 M at 30°C. A similar diffusion coefficient was obtained for Nafion 117 at 22°C by Hietala, Maunu, and Sundholm with the same technique. Kauranen and Skou determined the MeOH diffusion coefficient of 4.9 x 10 cm for Nafion... 

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