Resolution problems

Fig. 4-8. Diagrams showing two typical resolution problems. If the center of the Lai line of tantalum were at the vertical line near 1.515 A, incipient interference with the niobium lines could not be avoided on the usual analytical spectrogf ph.

The previous chapters are exclusively devoted to the measurements and interpretation of Fe spectra of various iron-containing systems. Iron is, by far, the most extensively explored element in the field of chemistry compared with all other Mdssbauer-active elements because the Mossbauer effect of Fe is very easy to observe and the spectra are, in general, well resolved and they reflect important information about bonding and structural properties. Besides iron, there are a good number of other transition metals suitable for Mossbauer spectroscopy which is, however, less extensively studied because of technical and/or spectral resolution problems. In recent years, many of these difficulties have been overcome, and we shall see in the following sections a good deal of successful Mossbauer spectroscopy that has been performed on compounds of... 

Single-line sources are now available which cut down the number of resonance lines in a spectrum and thereby reduce the resolution problems considerably. Since many laboratories have access to electron and ion accelerators to produce the parent nuclides Co and Cu, the major experimental obstacles to Ni spectroscopy have been overcome and a good deal of successful work has been performed in recent years. Moreover, the development of synchrotron radiation instead of conventional Mossbauer sources is of additional advantage for future Mossbauer applications (see below). 

Hirst You are suggesting that there is a resolution problem. I don t think this is a resolution problem we simply don t see STOCs in the absence of a stimulation. 

P.J. Gemperline and E. Cash, Advantages of soft versus hard constraints in self-modeling curve resolution problems. Alternating Least squares with penalty functions. Anal. Chem., 75, 4236 (2003). 

The work of Mosko [116] is important in that he is one of the few workers who have given serious consideration to the determination of nitrite in water. His paper is concerned with the determination of chloride, sulphate, nitrate, nitrite, orthophosphate, fluoride and bromide in industrial effluents, waste water and cooling water. Two types of analytical columns were evaluated (standard anion and fast run series). Chromatographic conditions, sample pretreatment and the results of interference, sensitivity, linearity, precision, comparative and recovery studies are described. The standard column provided separation capabilities which permitted the determination of all seven anions. The fast run column could not be used for samples containing nitrite or bromide owing to resolution problems. 

Another way of dealing with the resolution problem for powder lineshapes is to use multidimensional NMR techniques to separate powder pattern lineshapes (or magic-angle spinning sideband patterns) according to isotropic chemical shift, as mentioned previously. 

Borgen, O.S., Davidsen, N., Zhu, M.Y., and Oyen, O., The multivariate n-componcnt resolution problem with minimum assumptions, Mikmchim, Acta, 2, 1, 1986. 

Figure 7 shows that in powder XRD an ambiguity in contributions of lattice planes to diffraction peaks occurs and that a resolution problem... 

FIGURE 7-21. Example of use of gradient to solve the general resolution problem. (1) jS-Quinone. (2) 1,4-Naphthaquinone. (3) Anthraquinone. (4) 2-Methyl anthraquinone. (5) 2-Ethyl anthraquinone. (6) 2-Tert-butylanthraquinone. (a) Isocratic separation. Column Bondapak Cig/Corasil, 2.3 mm ID x 122 cm. Mobile phase methanol/water (50/50 v/v). Pressure 1200 psig. (b) First gradient attempt. Column same as in a. Mobile phase 0-100% methanol in water, (c) Successful gradient separation. Column same as in a. Mobile phase 30-70% methanol in water. 

The 70F method has the advantage that diffraction data can be collected to higher values of sin 6/X than with the monochromatic beam method. However, with larger unit cells there is a resolution problem at short wavelengths, where the powder lines may form a continuum [230, 231]. 

Analysis schemes developed for identifying clay minerals in the TEM based on EDS spectra (e.g., Murdoch et al.100) are inappropriate for colloidal samples dispersed on polycarbonate filters due to complications associated with the various sample-beam-substrate interactions that differ dramatically from that of ideal samples or standards with smooth polished surfaces.94 96 101 102 Correction procedures that account for the influence of particle size and morphology on x-ray spectra have been widely available for some time,101102 but these techniques have not been applied to the analysis of environmental particulates. To overcome the limitation of quantitative elemental analysis, some research groups have compared the x-ray spectra for sample colloids to the spectra for various minerals of similar size and composition under the same instrumental and sample preparation conditions to calibrate instrumental response.7 24 93 Noting the resolution problems associated with SEM analysis of submicron colloids, several research groups have chosen TEM as the primary discrete particle analysis technique,21 52 103 104 or have combined TEM analysis techniques, such as electron diffraction and x-ray microanalysis, to confirm conclusions drawn from SEM surveys.7,93 105... 

The marked dependence of 7( P—M— P) on stereochemistry for complexes of the platinum group metals has been used in NMR spectroscopy for several years 109,115). For methyl or tert-h xty tertiary phosphines, when the two phosphines are mutually trans then a triplet pattern results, but if the two phosphines are mutually cis, then a doublet pattern results as a consequence of the spectrum being of the AA X X type and the dependence of V( P—M— P) on stereochemistry. Exactly the same behavior is found in NMR spectroscopy with the advantage that the technique is far more versatile and is not normally troubled by resolution problems. Thus for cr-[RhCl3(CO)(PBu"2Ph)2] triplet patterns have been observed for six of the eight different carbon atoms in the tertiary phosphine ligand 164). When —M—is... 

Purely mathematical approaches using the PSF of the system and/or a priori object information rarely exceeded a factor of two [17,22,23] and were prone to producing artifacts. They can be augmented through additional a priori constraints, such as the objects featuring different absorption or emission spectra [24]. In this case, the resolution problem can become almost trivial, because objects with different spectra can be separated with suitable spectral filters. However, because of the difficulty to mark all features in a sample with different labels, reducing the resolution problem to a color separation... 

The 2 -resolution of any standard far-held light microscope is at least three times poorer than that in the focal plane which is particularly limited in 3D-imaging transparent objects such as cells. Therefore, in the quest for nanoscale resolution in far-held optical microscopy, it was most natural to start out with the axial resolution problem. 

Figure 2.20 Three possibilities to improve resolution. Problem separation of acetophenone (first peak) and veratrole. Original conditions column, 5 cm x 2 mm i.d. stationary phase, YMC-Pack ODS-AQ, 3gm mobile phase, 0.3 ml min water-acetonitrile (80 20) UV detector 254 nm. Arwas increased by using water-acetonitrile (85 15), all other conditions being unaltered, a was increased by using water-methanol (70 30). Afwas increased by using a column of 15 cm length under original conditions.

---