Impurities synergistic effects

Impurities and Combinations. MSDSs contain information on pure chemicals, known mixtures, and proprietary materials. Unfortunately there are no such sheets for other materials found in the laboratory, including solutions, mixtures of unknown or uncertain composition, and byproducts of reactions, all common in the laboratory. Impurities, synergistic effects, formation of unexpected products and byproducts, insufficiently clean equipment, and the combination of vapors from your experiment with that of your neighbor s can all produce sudden and unanticipated hazards. 

FBAs applied in combination may show a synergistic effect. Synergism is, at present, only of commercial interest with polyester brighteners. This phenomenon is discussed further in section 11.10. Conversely, the presence of a trace impurity in an FBA formulation may greatly reduce its effectiveness. In industrial laboratories much time and effort is expended in developing processes to minimise the content of such impurities or even to eliminate them completely. 

A dual-bed catalyst system has been developed to tackle the key problems in benzene product impurity during heavy aromatics transalkylation processing over metal-supported zeolite catalysts. It was found that by introducing zeolite H-Beta as a complementary component to the conventional single-bed Pt/ZSM-12 catalyst, the cascaded dual-bed catalyst shows synergistic effect not only in catalytic stability but also in adjustments of benzene product purity and product yields and hence should represent a versatile catalyst system for heavy aromatics transalkylation. 

The large group of inhibitors of free radical chain reactions are frequently used in combination with metal salts or organometallic stabilizers. They are amines, sulfur- or phosphorus-containing compounds, phenols, alcohols, or chelates. Aromatic phosphites at about 1 p.p.r. chelate have undesirable metal impurities and inhibit oxidative free radical reactions. Some of the more popular are pentaerythritol, sorbitol, melamine, dicyan-diamide, and benzoguanamine. Their synergistic effect is utilized in vinyl floors where low cost is imperative. 

Impurities in DNOC mixtures did not appear to cause an additive or synergistic effect in mice given intraperitoneal doses of DNOC (Harvey 1953). The intraperitoneal L[>° values for pure DNOC, 80% DNOC, and 33% DNOC were 24.2, 22.9, and 32.5 mg/kg, respectively. The 33% DNOC and 80% DNOC were contaminated with trinitro-o-cresol, which alone had an intraperitoneal LDso of 168 mg/kg. Clinical signs of DNOC toxicity were similar for all treatments. The authors suggested that contamination by trinitro-o-cresol did not lower the effective total toxicity of pure DNOC. 

Another explanation to the observed toxicity in some of the paints could be that the included chemicals exhibit synergistic effects and thereby together are more dangerous than the additive effect of the single chemicals. Impurities of the included chemicals could also be part of an explanation. 

DNNS is another commercially available acidic carrier used in PIM studies, which is normally supplied as a 50% solution in n-heptane. This means that a purification step may be required before use in order to eliminate the n-heptane and other impurities [25]. To the best of our knowledge, no purification step has been used so far prior to its application in the manufacturing of PlMs. It has been shown that the addition of DNNS to PDVts prepared with macrocyclic compounds as carriers (e.g., bis-PNP-lariat ether, p-cyclodextrin) produces a synergistic effect toward the target analyte [26,27]. 

Best quality obtainable by teehnology toughness, no deterioration in serviee, weldabdity. That is limits on alloy elements even more stringent than usual specifications (e.g. ASME) (C < 0.15. 25% for weldability and low transition temperature) low level of impurities taking into aceount possible synergistic effects. 

I. Silica. Silica is one of the secondary impurities, but it has synergistic effects in membrane cells when present along with calcium and aluminum [80]. It is difficult to remove silica from brine. The operator s best defense is prevention. Selection of salt, choice of dissolving conditions in order to reject as much silica as possible, and prevention of contamination by foreign substances are all important toward this end. 

Section 4.8 and its appendix discuss the action of iodine in more detail. It interacts with other elements to form other precipitates in either NaCl or KO service. These precipitates include barium paraperiodate, and so there may be a synergistic effect when both barium and iodine are present in the brine. Table 4.8.8 lists commercial brine specifications for some of the common membranes [202]. The allowable concentrations of barium and iodine may be related to each other or to operating current density. Table 4.8.9 lists the adverse effeets of various brine impurities. There are reports of physically distinct forms of Ba-I precipitates, with some very fine particles that form in regions away from the main current paths through the membrane [203]. These tend to have relatively little effect on membrane performance [204], and Section 4.8.S.3 also discusses the development of membranes with enhanced resistance to the effects of iodine. 

Impurities affecting membranes are generally divided into those affecting voltage (Mg, Ni, Fe) and those affecting current efficiency (Ca, Sr, Ba, Al, Si, I, SO4). Mechanisms can be complex, and synergistic effects are not uncommon. Examples of the... 

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