Degradation rapid

Antibiotics. Solvent extraction is an important step in the recovery of many antibiotics (qv) such as penicillin [1406-05-9] streptomycin [57-92-17, novobiocin [303-81-1J, bacitracin [1405-87-4] erythromycin, and the cephalosporins. A good example is in the manufacture of penicillin (242) by a batchwise fermentation. Amyl acetate [628-63-7] or -butyl acetate [123-86-4] is used as the extraction solvent for the filtered fermentation broth. The penicillin is first extracted into the solvent from the broth at pH 2.0 to 2.5 and the extract treated with a buffet solution (pH 6) to obtain a penicillin-rich solution. Then the pH is again lowered and the penicillin is re-extracted into the solvent to yield a pure concentrated solution. Because penicillin degrades rapidly at low pH, it is necessary to perform the initial extraction as rapidly as possible for this reason centrifugal extractors are generally used. [Pg.79]

If either dry powders or inverse emulsions are not properly mixed with water, large lumps of polymer form that do not dissolve. This not only wastes material, but can also cause downstream problems. This is especially tme for paper where visible defects may be formed. Specialized equipment for dissolving both dry polymers and inverse emulsions on a continuous basis is available (22,23). Some care must be taken with regard to water quaUty when dissolving polyacrylamides. Anionic polymers can degrade rapidly in the presence of ferrous ion sometimes present in well water (24). Some cationic polymers can lose charge by hydrolysis at high pH (25). [Pg.33]

Guar gum is a nonionic, branched-chain polysaccharide, a galactomaiman that is usually hydroxypropylated for use in drilling (52). It produces viscous solutions in fresh or salt water at concentrations of ca 3—6 kg/m (1—2 lb /bbl). It is used in soHds-free and low soflds muds and degrades rapidly above 80°C, limiting its use to shallow wells. [Pg.179]

Except for rho alumina, the activated aluminas are quite stable when mixed with water in the pH range from about 4 to 10. Below pH 2 and above pH 12 they degrade rapidly. [Pg.155]

Vinyhdene chloride is hepatotoxic, but does not appear to be a carcinogen (13—18). Pharmacokinetic studies indicate that the behavior of vinyl chloride and vinyhdene chloride in rats and mice is substantially different (19). No unusual health problems have been observed in workers exposed to vinyhdene chloride monomer over varying periods (20). Because vinyhdene chloride degrades rapidly in the atmosphere, air pollution is not likely to be a problem (21). Worker exposure is the main concern. Sampling techniques for monitoring worker exposure to vinyhdene chloride vapor are being developed (22). [Pg.428]

The limited thermal stability of the polymer, the polymer degrading rapidly above 195°C. [Pg.885]

In general, retention decreases as the modifier concentration increases because the modifier competes with the analytes for sites on the stationary phase. The effect on retention of changes in modifier concentration seems to be more pronounced for CSPs than for achiral stationary phases in SFC, and peak shapes are apt to degrade rapidly at low modifier concentrations [12]. Efficiency tends to decrease as the modifier concentration increases because analyte diffusion is slowed by the increased viscosity of the eluent [39]. [Pg.311]

The incretin effect is reduced in type 2 diabetes, and this is attributed, at least in part, to reduced secretion of GLP-1. The biological actions of GLP-1 remain essentially intact in type 2 diabetes, but administration of extra GLP-1 is not a practical therapeutic option because the peptide is degraded rapidly if A < 2 min) by the enzyme dipeptidyl peptidase IV (DPP-4). DPP-4 cleaves the N-terminal dipeptide from many of the peptides that have either an alanine or a proline residue penultimate to the N-terminus (Fig. 6). [Pg.122]

Most conducting polymers, such as doped poly(acetylene), poly(p-pheny-lene), and poly(/ -phenylene sulfide), are not stable in air. Their electrical conductivity degrades rapidly, apparently due to reaction with oxygen and/or water. Poly(pyrrole) by contrast appears to be stable in the doped conductive state. [Pg.151]

Chapter 13 is devoted to the PLC of namral pigments, which encompass fla-vonoids, anthocyanins, carotenoids, chlorophylls and chlorophyll derivatives, porphyrins, quinones, and betalains. Chromatography of pigments is especially difficult because many are photo- and air-sensitive and can degrade rapidly unless precautions are taken. [Pg.9]

Usually, simple Fe porphyrins degrade rapidly during catalytic reduction of O2 or of H2O2. [Pg.657]

Collman et al., 2007b]. However, when the electron delivery was slow, only the bimetallic forms manifested ORR catalysis (it was presumed that the monometallic Cu-free (Fe-only) catalysts degraded rapidly under these conditions) [Collman and Boulatov, 2002 Collman et al., 2007b]. [Pg.680]

The protocol will provide important date and time requirements. Estimated start and completion dates for the study are required by regulation. In addition, the Study Director may specify a maximum storage time of the RAC prior to processing if the chemical in question or its metabolites degrade rapidly. A maximum time after generation of a processed fraction before that fraction is placed into frozen storage may also be specified. A maximum storage time prior to shipment may also be specified. [Pg.225]

The current methodology to determine residues of alachlor, acetochlor, propachlor, and butachlor in crops and animal products was developed over the last two decades by researchers at the Monsanto Company. These herbicides degrade rapidly in plants and animals to numerous metabolites that can be hydrolyzed to common aniline moieties. Little to no parent herbicide is found as intact residue in crops and animal products therefore, the residue methodology focuses on the determination of the common moieties that are derived from the parent herbicides and their metabolites. Initially, gas chromatography (GC) with flame ionization detection, nitrogen-phosphorus... [Pg.344]

Since prohexadione-calcium degrades rapidly in soil, soil samples should be analyzed or frozen immediately after sampling. ... [Pg.538]

Since the methyl ester of prohexadione degrades rapidly in 1 M NaOH, it should not be handled under alkaline conditions. [Pg.538]

Azoxystrobin degrades rapidly and extensively in/on treated crops and in the environment. The residue definition of azoxystrobin in/on crops is for the parent compound only... [Pg.1168]

Polysilanes with alkoxy groups are more light sensitive than conventional polysilanes. They degrade rapidly in the presence of light in agreement with the facile formation of silylene from dialkoxydisilanes. Properties of these polymers are currently being investigated. [Pg.86]

We are interested in the effect of weathering on polymers for two distinctly different reasons. We may wish to retard it, so that our products survive longer in outdoor applications, or we may wish to accelerate it, so that products degrade rapidly when exposed to the elements. In either case, we need a way of predicting the response of polymers to the factors that produce measurable changes in their chemical and physical characteristics. Ideally, we would like to be able to obtain these results in as short a period of time as possible. [Pg.186]

Organic polymers have been used to increase the viscosity of acids. The primary application is in fracture acidizing. Binary and ternary acrylamide copolymers are the most commonly used chemicals for this application. Many of these polymers degrade rapidly in strong acids at temperatures >130 F development of more stable polymers suitable for high temperatures is desirable. Recently developed polymers for this application include acrylamide copolymers with ... [Pg.21]

Well Completion. In well completions it is essential that clean fluids are used, otherwise the production zone can become blocked and oil and gas flows reduced. This is particularly important if the structure is tight. It is also important that the polymer degrades rapidly and leaves little or no residue. [Pg.171]

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