Impurity in solvent

This of course applies especially to work done with very low c0 or with poorly purified solvents and reagents. Few investigations contain a plot of a rate or a rate-constant against cQ, from which C can be determined as the intercept on the c0 axis (the impurity intercept). A kinetic method of determining the concentrations of the impurities in solvent and monomer has been described (Holdcroft and Plesch, 1984). 

Small amounts of impurities in solvents usually do not have serious effects on the physical properties of solvents (Section 2.5). However, they often have drastic effects on the chemical properties of solvents, changing the reaction mechanisms or making electrochemical measurements impossible. The extent of the effect of an impurity differs considerably, depending on the properties of the impurity and those of the solvent in which it exists. Impurities that have significant effects on chemical reactions or on electrochemical measurements are called reactive impurities. 

This method is important in detecting and determining organic impurities in solvents. Today, gas chromatography-mass spectrometry (GC-MS) is also used to identify impurities. Water is sometimes determined by GC, with a column packed, for example, with Porapak Q. The lower limit of the water determination is 2 ppm. 

As water is a possible impurity in solvent NMA, it is somewhat reassuring that values for Aq for some of the hydrated and anhydrous alkaline earth salts agree so well. This also suggests that the ions in question are probably solvated moderately well in dilute solution by NMA molecules in competition with water molecules. 

The facile base-(amine-) mediated cleavage of the Fmoc group, as expected, raises problems regarding the amine impurities in solvents such as DMF, DMA, or which have to be... 

Solvent or impurities in solvent are not present in relevant concentrations in the tar matrix... 

The current allowable airborne exposure level for benzene as an impurity in solvent mixtures is 0.1 %. Benzene is also readily absorbed through the skin and those having dermal contact with solvents used for cleaning that contain 0.1% benzene contamination (the current allowable level) can be subjected to significant benzene absorption. In a study of workers who cleaned their hands with such solvents, the risk for leukemia was increased by 42%J161 This example points out the need for a more stringent regulation for the allowable concentration of benzene in solvent mixtures. The authors of the study cited recommend that the allowable level be reduced from 0.1 % to 0.01%. Other studies have made similar recommendations. 1171... 

Impurities are described in many texts on solvents [4, 5]. Many organic impurities can be identified by GC or GC/MS techniques for instance, MIBK can be found to contain mesityl oxide, the precursor to the manufacture of MIBK (Figure 4.6) [20]. Common impurities in solvents include H20, DMF [21], and AcOFl (in EtOAc and other solvents). Some solvents are inhibited with trace amounts of antioxidants, e.g., CH2C12 (stabilized with amylene or cyclohexane) andTFIF and 2-Me-THF (stabilized with BHT, butylated hydroxytoluene ). These impurities can influence the desired chemistry positively [22] and negatively, so and they should be considered. 

However, specificity is essentially a question of probabilities, and more use could be made of quantitative approaches to its evaluation (B27, B32, B33a). Even though no exact magnitude can be assigned to the concept of specificity, valid preferences can be established by the careful use of inequalities and known parameters of separation methods. Too many discussions of this topic are woefully inadequate because their authors use inappropriate parameters and functions of them. Some are theoretically sounder but fail to take account of well-known empirical problems such as the dangers of impurities in solvents and reagents. Finally, it should be obvious that the specificity claimed for a method of measurement is critically dependent upon the nature and source of the sample. 

The protonation state of the enzyme may be affected by acidic or basic reactants (starting materials or products). These species could act as described by either of the two sets of equilibria just presented. Acidic or basic impurities in solvents could also be significant here. 

Particularly in the analysis of trace amounts of alkaloids, e.g., in studies of metabolism, such minor impurities in solvents may have great influence. 

As we discussed above, the doping of polythiophene/IP composite is somehow inevitable, because (i) the ionization potential is only around 5 eV (ii) the material can only be prepared from solution, and during solvent evaporation the residual impurity in solvent is concentrated and (iii) the intrinsic defect in polymer chain or undefined end groups might act as dopant Certainly, the unintentional doping can be controlled in a low level. Therefore, let us consider the enhanced mobili-ty/conductivity from the role of carrier-dopant interactions. 

Sodium ions are a common impurity in solvents used for ESI. Analyte samples (especially proteins) are often contaminated by sodium ions in the production process, while sample solution storage in glass vessels also contributes to the sodium contamination. The extensive evaporation of solvent in the ESI process promotes solution ion-pairing reactions. When the analyte is a protein, ion-pairing reactions will involve Na and the ionized acid residues of the protein, see Eq. (1.16a). Similarly, impurity anions such as Cl will ion pair with ionized basic residues of the protein (see Eq. (1.16b)). 

M. Nagele, E. Pretsch, New method for determining the concentration of ionic impurities in solvent polymeric membranes, Microchim Acta, 121,269-279,1995. 

In the above definitions, C,yis the moiar concentration of i in the initial uniform mixture. For the desalination ratio, i is usually 2, corresponding to salt, which concentrates in region 2, whereas water concentrates in region 1 (ice in example II, Figure 1.1.2 purified water in example I, Figure 1.1.3). For the decontamination factor used with radioactive or surfactant impurities in solvents (or particles in air filtration), i is the impurity and j is the region for the purified solvent. These definitions need not be restricted to salt or a radioactive or surfactant impurity. They are... 

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