Optimum spectra

From the point of view of peak area uncertainty, the optimum spectrum size is 4096-8192 channels, depending upon the gamma-ray energy to be measured. 

It is first necessary to decide on the energy range required and from that the appropriate conversion gain (i.e. spectrum size). In Chapter 4, Section 4.6.8, it was explained that the optimum spectrum size is a balance between sufficient channels within the peaks of interest to aid computer deconvolution of peaks, bnt not so many that the statistical uncertainty on each channel snffers. The relationship in Equation (11.1) was snggested ... 

If the polymeric sample being examined is actually a sufficiently thin film, then it may be introduced directly into the sample compartment with no further preparation and examined by infrared transmission techniques, for example. It must be borne in mind that, with films examined by straight transmission, an interference pattern is often observed superimposed on the actual spectrum of the sample. Just as with low molecular weight organic substances, the variation in the band intensities observed for different functional groups means that, in order to obtain the optimum spectrum, the pathlength may differ significantly from sample to sample. The thickness of the film may need to be adjusted in order to obtain the best spectrum. 

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

Usually, the ultraviolet and visible regions of the spectrum are recorded. Many of the most intense emission lines lie between 200 nm and 400 nm. Some elements (the halogens, B, C, P, S, Se, As, Sn, N, and O) emit strong lines in the vacuum ultraviolet region (170-200 nm), requiring vacuum or purged spectrometers for optimum detection. 

Renilla luciferase. The luciferase of Renilla reniformis has been purified and characterized by Karkhanis and Cormier (1971) and Matthews et al. (1977a). The purified luciferase has a molecular weight of 35,000, and catalyzes the luminescence reaction of coelenterazine. The luciferase-catalyzed luminescence is optimum at pH 7.4, at a temperature of 32°C, and in the presence of 0.5 M salt (such as NaCl or KC1). The luciferase has a specific activity of 1.8 x 1015 photons s"1mg"1, and a turnover number of 111/min. The luminescence spectrum shows a maximum at 480 nm. The absorbance A28O of a 0.1% luciferase solution is 2.1. The luciferase has a tendency to self-aggregate, forming higher molecular weight species of lower luminescence activities. 

Involvement of ATP in the luminescence. Tsuji (1985) found that homogenate of the light organs of W. scintillans emits light when ATP is added in the presence of Mg2+. The luminescence reaction has a sharp pH optimum at 8.8 (Fig. 6.3.3), and the luminescence spectrum shows a peak at 470 nm (Fig. 6.3.4). The luminescence reaction... 

Davenport et al. (1952) were unsuccessful in their attempts to restore the luminescence of the filtered aqueous extract of Luminodesmus. Hastings and Davenport (1957) saw a weak luminescence in their filtered aqueous extracts made from the acetone powder of the millipedes. They found that the luminescence is dependent on pH, with an optimum at about pH 8.9, and that the light intensity could be increased by 10-30% by adding ATP. Hastings and Davenport also measured the luminescence spectrum of live animals, finding an emission peak at 495 nm. 

Selecting the optimum process encompasses a broad spectrum of possibilities (shape, size, material used, quantity, tolerance, time schedule, cost, etc.). There are designs when only one process can be used but there can be applications where different processes can be used. Each process, like each material of construction have their capabil-... 

For thermal reactions a variable temperature probe is necessary since optimum polarized spectra are usually obtained in reactions having a half-life for radical formation in the range 1-5 minutes. Reactant concentrations are usually in the range normally used in n.m.r. spectroscopy, although the enhancement of intensity in the polarized spectrum means that CIDNP can be detected at much lower concentrations. Accumulation of spectra from rapid repetitive scans can sometimes be valuable in detecting weak signals. 

Note The chromatogram zones exhibit a broad spectrum of colors [3, 12] that is very dependent on the duration and temperature of heating. Therefore the optimum reaction conditions must be determined empirically. With a few exceptions (ferulic, 4-amino-benzoic and cumarinic acids) aromatic carboxylic acids do not react [3]. The reagent in 80 ethanolic sulfuric acid is reported to be most sensitive for steroids [25]. 

Fig. 17—XPS spectrum of Si 2p peak for the TiN/Si3N4 nanocomposite coating with the optimum Si content of 10.8 at. % and the maximum hardness of 47.1 GPa.

Optimum values for the probabilities may not be obtained in the case that experimental llnewidths in the spectrum are very different since only a single linewidth is used for the simulated spectra. The calculated probabilities may be stored in the database and hard copy reports may be printed-... 

In uv absorbance detection, it is often useful to be able to detect different peaks in the chromatogram at different wavelengths. This may be because certain solutes have only a small absorptivity at the wavelength selected. At other times, a wavelength change can be used to edit out unwanted peaks. It is also useful to be able to record the spectrum of each component this can tell us the optimum detection... 

CW ENDOR spectrum measurements carried out at 120 K (the optimum temperature for measuring resolved CW ENDOR powder spectra of carotenoid radicals) shows resolved lines from the P-methyl hfc (Piekara-Sady et al. 1991,1995, Wu et al. 1991, Jeevarajan et al. 1993b) (see Figure 9.5). The lines above 19 MHz are due to neutral radicals according to DFT calculations (Gao et al. 2006). 

Fig. 5.9. Wavelength selection by Genetic Algorithm a 15 optimum wavelength selected from 86 of the full spectrum b relative fitness (rf/104) of the rim in dependence of the number of generations, above fitness of the best solution, middle mean, below fitness of the worst solution (Fischbacher et al. [1994/96 1995])... 

To analyze the green contamination on the small cups, the residue was removed using a micropipette and was placed onto a glass slide prior to recording its ATR spectrum, which is shown in Figure 37. The spectrum is shown together with the optimum-quality matches, which comprise materials such as an oil, a wax, and a defoamer. At the absorbance intensity recorded, the ATR spectrum recorded has all features associated with a saturated aliphatic hydrocarbon. 

For ratioed spectra, it is of interest to ascertain the effect of the various noise sources on the ratioed spectrum (i.e., the transmittance or reflectance spectrum as the case may be), on the absorbance spectrum, and also to determine, as was done previously [1, 2, 5], the optimum value for the sample to have that will give the minimum error of the calculated value. 

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