Solvent purity

Isocratic HPLC systems utilise a single mobile phase and are often preferred on the basis of cost, convenience and improved detector responses. This is especially true for refractive index or electrochemical detectors where the use of gradient systems is usually precluded. Additionally, isocratic elutions do not require column re-equilibration after each run, providing savings both in time and solvent. 

The main advantages of gradient over isocratic systems are provided in the analysis of unknown or multicomponent samples where a range of solvent strengths may be required both to ensure that aU the components loaded are eluted and also that the retention times of later eluting peaks are minimised. Gradient systems may be subdivided into two classes those where solvents are mixed prior to the pump (low pressure systems) and those where solvents are mixed after the pump (high pressure systems). 

In low pressure systems the gradient is generated prior to the pump and is delivered to the colunm in pulses determined by the dead volume of the pump head. Their main advantage is the relatively low cost. A simple system designed to generate a low pressure gradient has 

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The amount of solvent relative to the amount of total catalyst is usually large, and the amount of solvent relative to the number of active catalyst sites larger still very small amounts of inhibitors or poisons can have, therefore, large adverse influences on the rate of reduction. Solvent purity per se is of little regard in this connection, for gross amounts of innocuous impurities can be present without untoward effect. 

Apart from the above considerations, the distribution of a solute between two immiscible phases is always dependent upon temperature [128-130], solubility [131,132], resistance to degradation [133-135], solvent purity [130], and phase composition [136,137] (several reviews [130,132,138] give full details about the impact of these parameters on log determination). 

Criteria for solvent purity include careful measurement of physical constants such as melting point, refractive index, or conductance, but even these techniques may not detect some trace impurities. In many instances gas-liquid or other sensitive chromatographic methods may be used. 

The effects of concentration, rate of freezing, and solvent purity on the luminescence spectrum of dibenzothiophene have been studied.During slow freezing the molecules of the dissolved compound migrate toward the surface of the solvent crystals and thereby decrease the effective concentration. The effect on the triplet-singlet transition of introducing heavy atoms into the system has also been investigated by absorption measurements in benzene and ethyl iodide. ... 

Using a model system of H-STXOL/PNPCF/ C-methylamine we have found that we can reliably obtain a good yield of the STXOL/amine product if STXOL solubility and solvent purity are carefully controlled. However, the same reaction conditions generally fail to produce a useful [STXOL]n-protein (n<2) preparation. 

In the correct examples, complete sentences were used (achieved by adding the words were purchased from Aldrich ). Also, parentheses were used for solvent purity, making the solvent names easier to read. 

Gradient elution places special demands on solvent purity. Only carefully purified solvents should be used, and, it is recommended that prior to use they be passed over activated alumina or silica (7). The column acts as a collector of impurities which may elute as sharp peaks at a certain eluent composition and can be mistaken for sample components. It is therefore advisable to run the gradient first without injecting the sample in order to recognize the impurity peaks. 

There are three aspects of the question of solvent purity that have to be considered the specification of the purity of the given solvent its further purification, if necessary and the testing of the actual purity of the original or purified solvent. 

The feasibility of measuring p/sfa values in pure DMSO potentio-metrically by means of the glass electrode was first demonstrated by Kolthoff and Reddy (1962). This method was used by Ritchie and Uschold (1967) in evaluating the pK values of organic acids up to ca. 28. As shown by these workers, solvent purity is of paramount importance in attaining success by this method. 

For handling trimethylphosphine, solvent purity grades, and the reaction vessel, see the preparation of [(CH3)3P]2FeCl2 (Sec. A). 

Styrene-containing block copolymers are commercially very important materials. Over a billion pounds of these resins are produced annually. They have found many uses, including reinforcement of plastics and asphalt, adhesives, and compatibilizers for polymer blends, and they are directly fabricated into articles. Most styrene-containing block copolymers are manufactured using anionic polymerization chemistry. However, anionic polymerization is one of the more costly polymerization chemistries because of the stringent requirements for monomer and solvent purity. It would be preferred, from an economic cost perspective, to have the capability to utilize free radical chemistry to make block polymers because it is the lowest cost mode of polymerization. The main reasons for the low cost of FR chemistry are that minimal monomer purification is required and it can be carried out in continuous bulk polymerization processes. 

Low solubility of solvent into the silicon During epitaxial process, atoms of the solvent are incorporated in the Si crystal. Their incorporation can modify the electronic properties of the layer. Actually, many metallic impurities act as recombination centre or as dopant and reduce the lifetime of minority carriers. Solvent purity is also an important parameter to avoid other impurities. 

The written procedure should specify critical process steps and factors (such as extraction time, temperature and solvent purity) and acceptance criteria, as well as the type of validation to be conducted (e.g. retrospective, prospective or concurrent) and the number of process runs. 

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