Organic compounds as impurities

Determination of specific organic compounds as impurities in official pharmaceutical substances... 

DETERMINATION OF SPECIFIC ORGANIC COMPOUNDS AS IMPURITIES IN OFFICIAL PHARMACEUTICAL SUBSTANCES... 

Note Hydrochloric Acid is produced by various methods that might impart trace amounts of organic compounds as impurities. The manufacturer, vendor, or user is responsible for identifying the specific organic compounds that are present and for meeting the Requirements for organic compounds (below). Methods are provided for their determination under Tests. In applying the procedures, use any necessary standards... 

The TC detector and the FID are usually within a factor of two of the same response for an unknown organic compound as for other peaks in the run. This is a desirable property. Not only does it allow estimates to be made for the amount of unknown peaks, but it insures that there are no major volatile impurities if a chromatogram does not show them. This allows manufacturers of chemical products to specify the level of organic volatile impurities without identifying them in each case. 

Thermal decomposition of the hemihydrate vanadyl orthophoqihate, with partial or total loss of the hydration water, formation of new phases, and elimination of precursor impurities (chlorine ions, organic compounds) as well as of additives employed for powder tabletting in the case that the tablets are prepared before the dehydration stage. 

PEMFC contamination can also adversely impact membrane performance and life. The common impurities in fuel cell include anions, cations, CO, HjS, NH3, SO , NO, and volatile organic compounds. - Cationic impurities, including alkaline metals and ammonium, can infiltrate the membrane, considerably reducing performance. Metal ions, such as Fe + and Cu, can catalyze the radical formation reactions, strongly accelerating the chemical degradation of membranes in a PEMFC. Stainless steel is unsuitable as a material for end plates in PEMFCs. ... 

Solid organic compounds when isolated from organic reactions are seldom pure they are usually contaminated with small amounts of other compounds ( impurities ) which are produced along with the desired product. Tlie purification of impure crystalline compounds is usually effected by crystallisation from a suitable solvent or mixture of solvents. Attention must, however, be drawn to the fact that direct crystallisation of a crude reaction product is not always advisable as certain impurities may retard the rate of crystallisation and, in some cases, may even prevent the formation of crystals entirely furthermore, considerable loss of... 

Impurities in bromine may be deterrnined quantitatively (54). Weighing the residue after evaporation of a bromine sample yields the total nonvolatile matter. After removing the bromine, chloride ion may be deterrnined by titration with mercuric nitrate, and iodide ion by titration with thiosulfate water and organic compounds may be detected by infrared spectroscopy sulfur may be deterrnined turbidimetricaHy as barium sulfate and heavy metals may be deterrnined colorimetricaHy after conversion to sulfides. 

Benzyl chloride undergoes self-condensation relatively easily at high temperatures or in the presence of trace metallic impurities. The risk of decomposition during distillation is reduced by the use of various additives including lactams (43) and amines (44,45). Lime, sodium carbonate, and triethylamine are used as stabilizers during storage and shipment. Other soluble organic compounds that are reported to function as stabilizers in low concentration include DMF (46), arylamines (47), and triphenylphosphine (48). 

The effect of impurities in either structural material or corrosive material is so marked (while at the same time it may be either accelerating or decelerating) that for rehable results the actual materials which it is proposed to use should be tested and not types of these materials. In other words, it is much more desirable to test the actual plant solution and the actual metal or nonmetal than to rely upon a duphcation of either. Since as little as 0.01 percent of certain organic compounds will reduce the rate of solution of steel in sulfuric acid 99.5 percent and 0.05 percent bismuth in lead will increase the rate of corrosion over 1000 percent under certain conditions, it can be seen how difficult it would be to attempt to duplicate here all the significant constituents. 

Dissolution of CaCOs is a congruent reaction the entire mineral is weathered and results completely in soluble products. The above reaction is driven to the right by an increase of CO2 partial pressure and by the removal of the Ca and/or bicarbonate. Any impurities present in the calcareous rock, such as silicates, oxides, organic compounds, and others, are left as residue. As the calcium and bicarbonate leach... 

More than 3000 different enzymes have been extracted from animals, plants and microorganisms. Traditionally, they have been used in impure form since purification is expensive and pure enzymes may be difficult to store and use. There is usually an optimum temperature and pH for maximum activity of an enzyme. Outside these optimum conditions, activity may simply be held in check or the enzyme may become denatured , i.e. altered in such a way that activity is lost permanently, although some forms of denaturing are reversible. Many enzymes are also sensitive to transition-metal ions, the effect being specific to particular metal ions and enzymes. In some cases, certain metal ions are essential for the stability and/or activity of an enzyme. In other cases, metal ions may inhibit the activity of an enzyme. Similarly, certain organic compounds can act as enzyme inhibitors or activators. 

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