Concentration intensity ratio

Previous experience in arc and spark emission spectroscopy has revealed numerous spectral overlap problems. Wavelength tables exist that tabulate spectral emission lines and relative intensities for the purpose of facilitating wavelength selection. Although the spectral interference information available from arc and spark spectroscopy is extremely useful, the information is not sufficient to avoid all ICP spectral interferences. ICP spectra differ from arc and spark emission spectra because the line intensities are not directly comparable. As of yet, there is no atlas of ICP emission line intensity data, that would facilitate line selection based upon element concentrations, intensity ratios and spectral band pass. This is indeed unfortunate because the ICP instrumentation is now capable of precise and easily duplicated intensity measurements. 

Figure C2.3.18. Vibronic peak fluorescence intensity ratio (III/I) as a function of SDS concentration for 0.1 % PEO solutions o, —35 000 Daltons —600 000 Daltons). Open symbols are for aqueous solution without added salt, and filled symbols are for 100 mM aqueous NaCl. Reproduced with pennission from figure 2 of [111].

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

Quantification at surfaces is more difficult, because the Raman intensities depend not only on the surface concentration but also on the orientation of the Raman scat-terers and the, usually unknown, refractive index of the surface layer. If noticeable changes of orientation and refractive index can be excluded, the Raman intensities are roughly proportional to the surface concentration, and intensity ratios with a reference substance at the surface give quite accurate concentration data. 

Metals Dispersion from LEISS. Since He scattering Is very selective to Che outermost surface layer, one should anticipate that LEISS would be a valuable Cool for studies of metals dispersion for supported catalysts. For low oietal concentrations on high area supports, the (oietal/support) LEISS Intensity ratio should be directly proportional to metals dispersion. Recent stiidles In our laboratory have confirmed that expectation. 

Great progress has been made, however, in our later study using in situ SXS [Stamenkovic et ak, 2007a], where, by simultaneously fitting the intensity ratio between two different sets of crystal truncation rod (CTR) data that constrain the fit to the full CTR data [Robinson, 1986 Warren, 1990], it was possible to reveal the elemental concentration profile at the surface (Fig. 8.13c). Based on the in situ SXS results depicted in Fig. 8.13a, the topmost surface layer is confirmed to be 100 at%... 

When the fluorescence spectra of the probe shifts on protonation, two emission wavelengths with opposite proton-sensitive response are chosen to give a pH-dependent emission intensity ratio. In this ratio method a number of ion-independent factors that affect the signal intensity like photobleaching, variations in probe concentration, and illumination instability are eliminated. 

When the relation between then nonradiative decay processes and the concentration or value of the parameter of interest k A[Parameter]) is not linear (e.g., Eqs. (9.13 and 9.14), the intensity ratio of Eq. (9.31) introduces the well-observed problem of curvature in the Stem-Volmer plot (see Fig. 9.3). 

In the ratiometric method, the fluorescence intensity of the liposomes containing pyranine (F) and in the presence of the quencher DPX was determined at 520 nm upon excitation at two wavelengths 460 nm (of the charged unprotonated pyranine) and 415 nm (of the pH-independent isosbestic wavelength that describe the total pyranine concentration). The ratio of is described as F. The ratiometric measurement is used to determine the intraliposome aqueous phase pH (18,22). Then nigericin (or nonactine) at final concentration of 5pM was added to disrupt the pH and/or ammonium ion gradient that induce complete gradient collapse and the measurement at the above two excitations was repeated, and indeed it demonstrated a shift of the intraliposome aqueous pH to be identical to the extraliposome medium pH (10). 

Figure 25, Emission intensity from F atoms X = 703.7 nm) and Ar atoms (A,X = 750 nm) in a CF4/H2 plasma as a function 0/H2 concentration. The ratio ( ) of F/Ar emissions is also shown. (Reproduced with permission from Ref 115.)...

When the peak intensity ratio Ij/lj is measured for each of all the elements observed (carbon, oxygen, chromium and nickel), the surface atomic concentration ratio nj/nj of the elements can be given by the following equation, if surface contamination is negligible ... 

G. Pruckmayr, Du Pont, Delaweure The concentration of dormant ion is low. We can estimate the concentration of macro-cyclic plus lineeu dormant ions from the intensity ratio of the different Ct-methylene groups. The total is quite small in homopolymerizations, particularly at short reaction times. 

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