Impurities artifacts

Sample ores were surface collected from copper deposits throughout the eastern U.S. These samples represent small copper nuggets weighing approximately 200 mg and contained no matrix material or crystalline impurities. Artifact samples were removed from the sides and back of the artifact. In artifacts manufactured from multiple sheets, portions of each sheet were included in the sample. 

Crabtree RH (2012) Resolving heterogeneity problems and impurity artifacts in opoationally homogeneous transition metal catalysts. Chem Rev 112 1536-1554... 

Sample collection and work-up artifacts (D) exist, as do impurities and problems with the workers (experience, motivation, turnover, deadlines, and suboptimal training), all of which impact the quality of the obtained results. 

When JUNGLE2.dat and JUNGLE3.dat are analyzed with program CORREL, a plausible pattern turns up Impurities A, B, and C and the pH are mutually correlated impurity D is correlated with Titr and HPLC. The artifacts in JUNGLE3.dat cause a reduction in the strengths of correlation in four bins (three of them over two to four classes), and an increase in three bins over one class each. 

In some cases a principal components analysis of a spectroscopic- chromatographic data-set detects only one significant PC. This indicates that only one chemical species is present and that the chromatographic peak is pure. However, by the presence of noise and artifacts, such as a drifting baseline or a nonlinear response, conclusions on peak purity may be wrong. Because the peak purity assessment is the first step in the detection and identification of an impurity by factor analysis, we give some attention to this subject in this chapter. 

The weighted residuals plots in Fig. 3.4 are the results of the analyses, where the shape of the reference spectra are matched to those of acceptor and donor spectra by least-squares refinement. Poor shape-analysis leads to high weighted residuals, which can reveal impurities, decomposition, or other artifacts. In the present cases, no difficulties were encountered. 

The kinetic results reported by Jameson and Blackburn (11,12) for the copper catalyzed autoxidation of ascorbic acid are substantially different from those of Taqui Khan and Martell (6). The former could not reproduce the spontaneous oxidation in the absence of added catalysts when they used extremely pure reagents. These results imply that ascorbic acid is inert toward oxidation by dioxygen and earlier reports on spontaneous oxidation are artifacts due to catalytic impurities. In support of these considerations, it is worthwhile noting that trace amounts of transition metal ions, in particular Cu(II), may cause irreproducibilities in experimental work with ascorbic acid (13). While this problem can be eliminated by masking the metal ion(s), the masking agent needs to be selected carefully since it could become involved in side reactions in a given system. 

The apparent reduction in GCH ) at the higher irradiation temperature used in this work is believed to be an artifact due to a reduction in the hyrocarbon impurities in the samples used in this study compared with the work of Brown and O Donnell (1,2). 

Developing an isolation approach is an activity that is frequently overlooked or addressed as an afterthought. However, solubility and stability data may dictate the development of a chromatographic method that requires the elaboration of the isolation, that is, it is more complicated than a simple evaporation of the mobile phase. The development of the chromatographic process should be linked to and interactively codeveloped with the isolation. Ideally, the isolated impurity sample should not contain other compounds or artifacts, such as solvents, mobile-phase additives or particulate matter from the preparative chromatography, as they may interfere with the structure elucidation effort or adversely affect the stability of the impurity during the isolation process. Therefore, it is preferable to avoid or minimize the use of mobile-phase additives. However, should this prove to be impossible, the additive used should be easy to remove. The judicious choice of mobile phase in the HPLC process increases the ability to recover the compound of interest without or with minimum degradation. The most common... 

In addition to the precautions already mentioned, the time of column equilibration between each run should be about the same. Ideally the profile of one of the two peptides (native or synthetic) should give a symmetrical absorbance as well as show the presence of a small amount of an impurity. Under such circumstances, the coelution run should show a symmetrical absorbance of the size of that of the synthetic and native molecules. In addition, the absorbance of the impurity should now be half the size of that seen in the chromatogram of the contaminated peptide. All other absorbances such as injection artifacts should be identical in all runs 2-6. CAUTION Two peptides that show the same retention times after being run separately under the same conditions cannot be said to have coeluted ... 

Archaeomagnetism can be considered a branch of Paleomagnetism specifically devoted to the dating of archaeological materials from the measurement of the remanent magnetization achieved by the iron oxide impurities present in clay after cooling of the ceramic artifact. This recording mechanism primarily provides information on the direction of the Earth s field at the time the artifact was fired or the kiln was last used. 

During the long burial period, extended redistribution of material has taken place. While metal went outwards, ions like chloride and impurities from the environment diffused inwards, resulting in a mass of corrosion products that occupies a volume approximately double the initial size. As a consequence, part of the artifact remains... 

Batch solvent extraction methods (e.g., by separatory funnel) for the preparation of extracts for biological analysis have a number of major problems. A large volume of solvent must be evaporated after the extraction step in order to obtain a sample sufficiently concentrated to be useful for biological testing. Artifacts can occur from solvent impurities, and reactions can occur during the evaporation process. 

An even better way to determine absolute rate constants is to use pre - steady state kinetics to measure the rate constants for the formation or decay of enzyme-bound intermediates (Chapter 4). The rate constants for first-order exponential time courses are independent of enzyme concentration and so are unaffected by the presence of denatured enzyme. The impurity just lowers the amplitude of the trace. Pre-steady state kinetics are also less prone to artifacts, discussed next, that are caused by the presence of small amounts of contaminants that have a much higher activity than the mutant being analyzed. The steady state kinetics of a weakly active mutant could be dominated by a fraction of a percent of wild type. In pre-steady state kinetics, however, that contaminant would contribute only a fraction of a percent of the amplitude of the trace. This would be either lost in the noise or observed as a minor fast phase. 

One of the main values of fluorescence as a technique for probing protein conformation is that it is highly sensitive and very economical of material. This means, however, that small traces of fluorescent impurities in the solvent or on the cell are readily detected and, if care is not taken, can lead to misinterpretation of the spectra. The essential aim in using this technique, therefore, must be to obtain a fluorescence emission spectrum for a protein that is guaranteed free from all too easily generated artifacts. 

There have been reports of significant concentrations of isomeric artifacts in the commercial coenzyme standards (83-87). Because the coenzymes are the predominant vitamers in most foods, failure to account for these impurities during quantitation of the coenzymes could result in significant analytical errors. Several methods have been suggested to compensate for the lack of purity in the commercial coenzyme preparations (83-85,88,89). 

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