Optical density traces

Figure 6. Schematic of toner deposits and optical density traces, obtained using a slit aperture, of large particles (left), and small particles (right).

J. D. Ellis, K. L. Scott, R. K. Wharton, and A. G. Sykes, Inorg. Chem. 11, 2565 (1972), who observe optical density changes when 1 M acid solutions are mixed with water in a Durrum-Gibson stopped-flow apparatus. Such traces could be incorrectly assigned to chemical reactions. 

Measured extinction spectra for aqueous suspensions of polystyrene spheres—the light scatterer s old friend—are shown in Fig. 11.19. Water is transparent only between about 0.2 and 1.3 jam, which limits measurements to this interval. These curves were obtained with a Cary 14R spectrophotometer, a commonly available double-beam instrument which automatically adjusts for changing light intensity during a wavelength scan and plots a continuous, high-resolution curve of optical density. To reproduce the fine structure faithfully, the curves were traced exactly as they were plotted by the instru-... 

Recently, a similar technique has been used (40) to demonstrate the conversion of the neutral H atoms (G 0.5) to e aq. Figure 3 shows an oscilloscope trace obtained with 2.4 X 10 2 M OH at 5780 A., optical path = 80 cm. (no H2). (See (45) for details about the technique.) The initial small increase in optical density is caused by the Reaction 7. This increase is very small, because Gh — 0.2 Ge. The results agree with those obtained with 0.1 M H2, but we did not make any quantitative analysis. 

It has proven feasible to take the electrical output from photocells or phototubes and either with or without amplification record the magnitude and duration of the output. The recording may be made either in the form of a line tracing on a moving chart or may be converted to numerical values and printed by a read-out device. Further refinements can be supplied in which the instrument converts optical densities (or transmittance units) to concentration values. More intricate recording colorimeters or spectrophotometers are also available for continuous scanning and recording of complete spectra from ultraviolet to infrared. No further discussion of these will be attempted since they do not serve a normal function in routine clinical chemistry laboratories. 

Figure 37.4 Replicate Pseudo-nitzschia multiseries cultures were grown under 24 h light (100 tmol photons s ) at 15 °C for 4 days as an auxostat (chemostat with growth limited by pump rate) with Si-limited f/2 media. On day -4, the pumps were turned off, forcing the cultures into Si-limitation. On days 0, 4 Si-spikes (10 pM) were added. On day 5, trace-metals (f/2 stock) was added, with no apparent response. Optical density (cell abundance) and variable fluorescence were determined from a PAM fluorometer and are plotted versus time (dashed vertical lines indicate additions of unenriched seawater dashed horizontal line indicates maximal Fv/Fm values in healthy cells). A rapid decline and recovery of variable fluorescence indicates impaired photosynthetic performance, and functionally mimics the response of Fe-limitation, with recovery times dependent on the length of time spent in Si-deprived conditions.

A typical oscilloscope trace is shown in Figure 5. (The decay rate did not change when the argon pressure was varied from 58 to 95 atm., or when the benzene pressure was changed from 2 to 8 cm.). The absorption did not decay to zero, but seemed to reach a plateau of about half of the maximum optical density. Because of noise and the difficulty of establishing the plateau, first and second order tests on such decay... 

Figure 4. Oscilloscope traces, plotted on O.D. paper, taken at pH = 13, in hydrogen peroxide solutions containing 0.05 atmospheres N20. The solid line in (a) represents the average change of the measured optical density with time.

Besides the phenolic fraction, Myers and Singleton (1979) and Voyatzis (1984) identified a non-phenolic fraction in aU types of wines. It consists mainly of polysaccharides and protein compounds, but also contains tyrosol and traces of catechins. The non-phenolic fraction represents 50% of the nltraviolet absorption of dry white wines and, therefore, affects the optical density at 280 nm so that this valne cannot be considered to express the phenolic composition alone. In sweet white wines, this fraction has a high concentration of nitrogen componnds and represents more than 50% of absorption at 280 nm. 

Fig. 4. Representative stopped-flow traces comparing the time course for the formation of the enzyme-NADH binary complex measured at 365 nm (trace A) with the time course for the uptake of hydrogen ions as measured by the Thymol Blue spectral changes at 650 nm (trace B). Trace C measures the optical density at 330 nm, the isobestic point for the two NADH species enzyme bound and free in solution, see insert to this figure. Traces A and C were measured in 0.5 mM sodium pyrophosphate bufier (pH 8.80 0.1). In trace B, 0.65 mM Thymol Blue, pH 8.8 0.1, is the dominate buffer ion present in solution. Conditions E, 10.6 yuN NAD+ 23.9 /iM NADH, 94.1 yuM Thymol Blue, 0.384 mM pH 8.8 0.1 and 25.0 ...

The kinetic method involves readings V(), such as titer, optical density, optical rotation, volume of a gas, areas under vapor-phase chromatograph traces, etc., taken during the course of a reaction and at times zero ( q) and infinity (v ), respectively. This leads, when the reaction is of first order, to equation (23) (written for practical purposes in two forms, 23a and 23b), in which k is the specific reaction rate... 

Hefendahl [30] discovered that there is a linear relationship between the extinction area of a spot on the densiometric trace of a chromatogram and the weight of material in the spot. To make the chromoplate translucent he sprayed the adsorbent with an ethereal solution of paraffin and then measured the optical density of the chromatogram as a function of the distance from the origin (Figure 5.4). The area under the peak, measured... 

Fig. 15. Parallel increase in the relative amounts of L protein(s) and chlorophyll synthesis during greening of y-1 cells. The amount of L protein(s) is represented as the ratio of optical density of the corresponding peak to peak 7, which does not change during the greening, as calculated from densitometer tracings of electrophoretograms of membrane proteins. (O----O), L proteins in light (A---A), chlorophyll in light ( --- ), L proteins in dark (A---A), chlorophyll in dark. (For experimental details, see ref. 70.)...

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

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