Absorbance curves

Adaptations of this method have been proposed in order to take into account the band displacement due either to substitution on the aromatic ring, or to chains of different lengths. The variations consist, instead of measuring the absorbance at maximum absorption, of an integration of the absorbance curve over a specified range (Oelert s method, 1971). More exact, this method is used less often mainly because the Brandes method is simpler... 

Molecules such as 3,4 and 5 in Figure 2.6, which have a zero velocity component away from the source, behave uniquely in that they absorb radiation of the same frequency Vj-es whether the radiation is travelling towards or away from R, and this may result in saturation (see Section 2.3.4). If saturation occurs for the set of molecules 3, 4 and 5 while the radiation is travelling towards R, no further absorption takes place as it travels back from R. The result is that a dip in the absorbance curve is observed at Vj-es, as indicated in Figure 2.5. This is known as a Lamb dip, an effect which was predicted by Lamb in 1964. The width of the dip is the natural line width, and observation of the dip results in much greater accuracy of measurement of v es. 

Construct a concentration-absorbance curve with the aid of the standard tin solution. 

Fig. 3. Visible—C/K absorbance curves for the rearrangement of N-nitroso-N-methylaniline in...

Figure 16 Comparison of the in vitro (filled circles) and the individual percent absorbed (curves) following the administration of core I devices to dogs. (From Ref. 24.)... 

Many practical applications of cure characterization involve samples for which the data required to convert isocyanate absorbance to concentration is unavailable. The emphasis is often placed on rapid analysis of many samples rather than an exhaustive characterization of a single sample. It is particularly desirable to develop a procedure which can determine the rate constants describing the cure reaction without converting the infrared absorbance curve to concentration. This has been accomplished by normalizing the data in such a way that the rate constants are determined from the shape of the cure curve. 

The second derivative is both simpler and more complicated to deal with. As we saw, the second derivative is maximum at the wavelength of the peak of the underlying absorbance curve, and we noted previously that the numerator term at that point increases... 

Figure 56-10 The difference between the ordinates of two points equally spaced around pt + a as a function of the spacing. In this figure the underlying absorbance curve has a bandwidth of 20 nm.

Unless standards are prepared in buffered media, positive or negative deviations may result from measurements made at 348 nm or 372 nm respectively Alternatively, measurements can be made at the isosbesticpoint, i.e. where the absorbance curves of each form intersect, and where absorbance is not a function of equilibrium concentrations but only of the overall concentration. Solutions of weak acids and bases should also be measured at their isosbestic points for the same reason. 

Fig. 3.5.18 Absorbance curves (corrected for the absorbance of the quartz) for H2S-exposed CdBe, immersed in CHC13 and subsequently immersed in 2.5 X 10 1 M HgCL for 0, 10, 50, and 110 min (total immersion times). (From Ref. 64.)...

Fig. 25. Sensitized anti-Stokes delayed fluorescence from naphthalene.60 (1, 2) Delayed fluorescence from 10 "s3/ phenanthrene, and from mixture of phenanthrene (10"W) and naphthalene (3 X 10-3M), in ethanol. (3) Normal fluorescence from solutions 1 and 2 at 260 times less sensitivity. (4) Spectral distribution of exciting light for curves 1, 2, and 3, 0.7 X IQ-8 einstein liter"1 sec.-1 absorbed. (5, 6) Normal and delayed fluorescence from 3 X 10 lM naphthalene in ethanol excited by 313 m/i, 2 X 10-4 einstein liter-1 sec.-1 absorbed. Curve (5) at a sensitivity 100 times less than curve (6). Temperature for all curves was — 72° 3°C.

Figure D2.1.1 UV absorbance of sunflower oil samples dissolved in 2,2,4-trimethylpentane. An unoxidized sample (dashed line) and an oxidized sample (solid line) showing the characteristic absorbance peak for conjugated dienes (CDs) at 233 nm as well as peaks at 268 and 278 nm corresponding to conjugated trienes (CTs). The plot in the upper right corner shows an enlarged view of the absorbance curve in this region.

Figure 4- Relation of dose to absorbance curve of various initial cupric ion...

Figure 7. Relation of irradiation time to absorbance curves for fresh preirradiated and stored solutions of standard ferrous-cupric dosimeter...

Figure 4.2 Weights for monochromatic primaries located at 620 nm, 530 nm, and 400 nm for an observer whose response characteristics are described by the absorbance curves of the retinal curves as measured by Dartnall et al. (1983).

A color unit based on the absorbancy curve of a standard, white sugar was proposed by Peters and Phelps.3 This particular sugar had an absorbancy index at 560 mg of 0.00485. It was not intended that the white sugar... 

These results were further elaborated by measuring the silane loss over short leaching times for samples cured in air and under vacuum.35 Dehydrated mesoporous silica gel was modified with APTS or APDMS in dry toluene (1 % v/v silane/toluene). Curing was performed for variable times in air at 383 K or under vacuum at 423 K. For UV tests the modified silica was stirred in a salicylic aldehyde/ethanol solution. At indicated times a Sml sample was taken, centrifuged and the supernatant was measured at 404 nm. The loss curves of APTS for variably cured samples are displayed in figure 9.17. The position and profile of the absorbance curves are indicative for the stability of the coating under study. 

Figure 7. Uncalibrated VCD absorbance curves (upper) and ordinary absorbance (lower) for a-pinene. The signs of the enantiomers and the racemic mixture of a-pinene are indicated. The spectra on the left were take with the lens focusing optics and those on the right with the ellipsoidal mirror focusing optics.

Based on integral color estimated from absorbency curve from 400 to 700 mu determined with a Cary recording spectrophotometer. All liquors were buffered to pH 7 prior to measurement. 

The transmittance and reflectance spectra of an undoped AP-CVD ZnO film and of a doped AP-CVD ZnO Al film are shown in Fig. 6.40. While the transmittance of the undoped film stays over 80% along the whole visible range, the transmittance of the doped film displays a pronounced drop in the near-infrared wavelength range. The drop corresponds to a minimum in the reflectance curve, as well as to a maximum (peak) in the absorbance curve. This occurs close to the so-called plasma frequency. These effects are due to free carrier absorption. When N is increased, the plasma frequency is shifted towards shorter wavelengths, and the drop in optical transmittance becomes more pronounced. This is illustrated for the case of LP-CVD ZnO.B films in... 

A second procedure for obtaining dye concentrations from absorbance data was developed for very complex dye mixtures. In this procedure the absorbance of the spent dyebath was measured at 16 equally-spaced wavelengths from 400 to 700 nm. The dye concentrations were determined from a least-squares fit of the absorbance curve at these 16 wavelengths. A computer program in FORTRAN IV was developed to determine the concentrations of up to six dyes in a mixture by the sixteen-point technique. 

Relative rates of photocoloration ( colorabilities 24) have been determined as slopes of the D(t) - / absorbance curve obtained by measurement of the rate of... 

Dimethyl Sulfoxide Use a pure grade of dimethyl sulfoxide (99.9%, melting point 18°) that has a clear, water-white appearance has an absorbance curve, compared with water, not exceeding 1.0 at 264 nm and shows no extraneous impurity peaks in the wavelength range up to 350 nm. Store in glass-stoppered bottles. 

Figure 1. Optical conversion efficiency for solar energy as a function of threshold wavelength of the absorber. Curve I is a plot of the fraction of incident solar power (percent) available at various threshold wavelengths Curve II is a plot of the thermodynamic conversion efficiencies under optimal rates of energy conversion.

---