Solvent impurities

Hydrochloric Rubber-lined steel Low tolerance for organic solvent impurities temperature limited... 

Figure 12.7 Cliromatograms of a polycarbonate sample (a) microcolumn SEC ti ace (b) capillary GC ti ace of inti oduced fractions. SEC conditions fused-silica (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at aElow rate of 2.0ml/min injection size, 200 NL UV detection at 254 nm x represents the polymer additive fraction ti ansfeired to EC system (ca. 6 p-L). GC conditions DB-1 column (15m X 0.25 mm i.d., 0.25 pm film thickness) deactivated fused-silica uncoated inlet (5 m X 0.32 mm i.d.) temperature program, 100 °C for 8 min, rising to 350 °C at a rate of 12°C/min flame ionization detection. Peak identification is as follows 1, 2,4-rert-butylphenol 2, nonylphenol isomers 3, di(4-tert-butylphenyl) carbonate 4, Tinuvin 329 5, solvent impurity 6, Ii gaphos 168 (oxidized). Reprinted with permission from Ref. (14).

No solvent-stripping or recovery process is required, and product contamination by solvent or solvent impurities is avoided. The chemical reaction may take place in the melt... 

GL18 Impurities Residual Solvents Impurities residual solvents in new veterinary medicinal products, active substances and excipients... 

Fortunately, this backgronnd is often less of a problem than might be anticipated from the above. The majority of ionization techniques employed in LC-MS are soft ionization techniqnes which provide primarily molecular ions that occur at relatively high values of mass-to-charge ratio (m/z), rather than fragment ions which occur at relatively low m/z values. In the majority of cases, the molecular weight of the analyte is higher than those of the solvent impurities and the effect of these may therefore be minimized. 

Sewage/water Auxiliaries (Isolation) Solvents Impurities Catalysts... 

Consider the case of the production of peroxy esters (e.g. tert-buty] peroxy 2-ethyl hexanoate), based on the reaction between the corresponding acid chloride and the hydroperoxide in the presence of NaOH or KOH. These are highly temperature sensitive and violently unstable, and solvent impurities are detrimental in their applications for polymerization. Batch operations to produce even 1000 tpa will be unsafe. A continuous reactor can overcome most of the problems and claims have been made for producing purer chemicals at lower capital and operation cost the use of solvent can be avoided. Continuous reactors can produce seven to ten times more material per unit volume than batch processes. Since the amount of hazardous product present in the unit at any given time is small, protective barrier walls may be unneccessary (Kohn, 1978). 

Solvent Extraction Aqueous sample is partitioned with an immiscible organic solvent. Extraction efficiency depends on the affinity of the solute for the organic solvent. All sample types Samples with a high affinity for water are not extracted. Extractions can be performed by a simple single equilibration or by multiple equilibrations with fresh solvent. Solvent impurities concentrated along with sample. 

Solubilizing all or part of a sample matrix by contacting with liquids is one of the most widely used sample preparation techniques for gases, vapors, liquids or solids. Additional selectivity is possible by distributing the sample between pairs of immiscible liquids in which the analyte and its matrix have different solubilities. Equipment requirements are generally very simple for solvent extraction techniques. Table 8.2 [4,10], and solutions are easy to manipulate, convenient to inject into chromatographic instruments, and even small volumes of liquids can be measured accurately. Solids can be recovered from volatile solvents by evaporation. Since relatively large solvent volumes are used in most extraction procedures, solvent impurities, contaminants, etc., are always a common cause for concern [65,66]. 

Extraction or dissolution almost invariably will cause low-MW material in a polymer to be present to some extent in the solution to be chromatographed. Solvent peaks interfere especially in trace analysis solvent impurities also may interfere. For identification or determination of residual solvents in polymers it is mandatory to use solventless methods of analysis so as not to confuse solvents in which the sample is dissolved for analysis with residual solvents in the sample. Gas chromatographic methods for the analysis of some low-boiling substances in the manufacture of polyester polymers have been reviewed [129]. The contents of residual solvents (CH2C12, CgHsCI) and monomers (bisphenol A, dichlorodiphenyl sulfone) in commercial polycarbonates and polysulfones were determined. Also residual monomers in PVAc latices were analysed by GC methods [130]. GC was also... 

A BLM can even be prepared from phospholipid monolayers at the water-air interface (Fig. 6.10B) and often does not then contain unfavourable organic solvent impurities. An asymmetric BLM can even be prepared containing different phospholipids on the two sides of the membrane. A method used for preparation of tiny segments of biological membranes (patch-clamp) is also applied to BLM preparation (Fig. 6.10C). 

Fig. 19 The proton NMR spectrum of [Fe(HC(pz)3)2](BF4)2 obtained at 223 K, a, where the stars indicate solvent impurities, and at various temperatures, b. In b the vertical scales of the spectra have been expanded driving the diamagnetic resonances off scale. Plots obtained from [46]... 

Generally, y depends on the purification methods and is a function of the monomer concentration ideally it should be reproducible and not greater than 10% of [Int]0. On a plot of k1 against [Int]0 the intercept on the [Int]0 axis (the impurity intercept ) due to solvent impurities is usually the major part of y, the contribution from impurities of... 

Solutions in a conductance cell are often stirred to hasten salt dissolution, to promote solution mixing, or to prevent temperature gradients. Some workers observe an upward drift in measured resistances of unstirred solutions 12-17) while others report a downward drift unless the unstirred solution is mixed by shaking of the cell immediately before the measurement9-18-26>. The magnitude of this change is often 0.1 % or more. The effect has not been observed in other cases 8>10). The source of this problem has been variously attributed to temperature variations, electrode adsorption effects and solvent impurities, although the problem has not been analyzed in detail. In all but one of the above cases 12> the resistance of the stirred solution was taken as the true value. 

Toxic pollutants found in the wastewater streams are normally related to solvents and solvent impurities, product additives, and cooling water treatment chemicals. Table 7 presents a listing of the potential wastewater sources and the associated contaminants for this industry. 

For these reasons, an understanding of the purification conditions and materials used is useful. For example, on using one solvent, impurities could crystallize under the same conditions as the compound of interest, but on using another solvent, the impurities may be left in the solution. Use of a relatively nonvolatile solvent may lead to residual amounts, which are difficult to eliminate. If the drug substance is dissolved in a solvent, filtration is an effective method of removing particulate matter. 

Impurities, in contrast to degradation products, might or might not have any relation to the drug molecule. In the simplest case, residual quantities of a solvent used at some step in the process chemistry can become an impurity in the drug product. A recent, very extensive publication to which the interested reader is referred, listed the proton and carbon NMR chemical shifts of a large number of potential solvent impurities in a number of commonly employed NMR solvents [22]. There have also been several reviews on the topic of residual solvents in pharmaceuticals [23, 24]. 

Various transfer agents (denoted by S or XA as in Chap. 3), present as solvent, impurity, or deliberately added to the reaction system, can terminate the growing polymer chain by... 

Tetrahydrofuran (THF, UV grade) was used as the mobile phase throughout this work since the extent of fractionation could be demonstrated by direct analysis of the preparative fractions without the need for concentration. When samples are to be recovered by removal of solvent, other mobile phases (methylene chloride, etc.) may be preferred to avoid concentrating solvent impurities which are formed in THF on exposure to air unless additional precautions are taken. 

Solvent impurities in cephalosporin analysed by sampling of the head space above a heated DEG solution of the drug. Separation was carried out on column (10 feet x 1/8 in i.d.) packed with Porapak Q. Reproduced with permission from J. Chromatology (see Reference 8). 

For difficult separations, multiple extractions are frequently carried out, although in many cases the background is also coextracted. Using multiple extractions, polar interferences may sometimes be transferred from the aqueous into organic solvents that can dissolve minute amounts of water. This problem cannot be eliminated by simple presaturation of the extraction solvent but only by washing the extract with small amounts of water (58). Another relevant issue to be considered in trace residue analysis concerns the purity of the organic solvents, since they can introduce solvent impurities into the sample extract. Therefore, the need for high solvent purification should not be overlooked in some applications. 

With aromatic hydrocarbons, the potential of this step is usually 0.5 V more negative than the first step. The dianions Q2 are more protophilic (basic) than Q and are easily converted to QH2 (or QH ), withdrawing protons from the solvent or solvent impurities (possibly water), although Q2 with delocalized charges can remain somewhat stable. With compounds like 9,10-diphenylanthracene and in protophobic solvents like AN, the formation of dications has been confirmed in the second oxidation step (Section 8.3.2) ... 

For the Fc+/Fc and BCr+/BCr couples, the electrode reactions are reversible or nearly reversible in most non-aqueous solvents and the half-wave potentials are not much influenced by solvent impurities such as water. Thus, the half-wave potentials will not vary widely even when they are measured by different persons or at different laboratories. Moreover, the potentials of the Fc+/Fc and BCr+/BCr couples are considered almost solvent-independent. This justifies the comparison of potential data in different solvents, as far as they are based on this proposal. The data in Table 6.4 are useful in determining the mutual relations between the potentials of the Ag+/Ag and Hg2+/Hg electrodes and the Fc+/Fc and BCr+/BCr cou-... 

In previous chapters, we dealt with various electrochemical processes in non-aque-ous solutions, by paying attention to solvent effects on them. Many electrochemical reactions that are not possible in aqueous solutions become possible by use of suitable non-aqueous or mixed solvents. However, in order for the solvents to display their advantages, they must be sufficiently pure. Impurities in the solvents often have a negative influence. Usually commercially available solvents are classified into several grades of purity. Some of the highest-grade solvents are pure enough for immediate use, but all others need purification before use. In this chapter, the effects of solvent impurities on electrochemical measurements are briefly reviewed in Section 10.1, popular methods used in solvent purification and tests of impurities are outlined in Sections 10.2 and 10.3, respectively, and, finally, practical purification procedures are described for 25 electrochemically important solvents in Section 10.4. 

A value for the equivalent conductance at infinite dilution for lithium bromide in acetone was first calculated in 1905 by Dutoit and Levier (13) for 18°C 166 12 1 cm2 eq-1. A graphical method involving Ostwald s dilution law (A-1 = Ao-1 + cA/KdAq2), applied to their data in 1913 by Kraus and Bray (14), produced values of 5.7 X 10 4 for Kd and 165 12 1 cm2 eq-1 for Aq. Deviations from the mass action law (nonlinearity in the graph) become appreciable at concentrations of ca. 10 3N. Both groups pointed out that measurements in acetone are liable to error from several sources, including the presence of solvent impurities and exposure to light. A solvent correction of 21% was applied to their most dilute solution. 

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