Avoiding contamination

Allow the reddish-yellow solution to cool to about 40° and then filter off at the pump the polyene which has separated this filtration should be performed as rapidly as possible to avoid contamination with lead acetate, and a Buchner funnel of not less than 6 cm. diameter should therefore be used to avoid clogging the filter. Wash the crude production the filter with... 

Stoppers. Those fitted with 514,519, and 524 cones are useful sizes. Stoppers with flat heads are to be preferred, since they may be stood on end when not in pse, thus avoiding contamination of the ground surface. An additional refinement is the provision of a finger grip as in Fig. II, 56,1. 

A gun is used to direct a beam of fast-moving atoms or ions onto the liquid target (matrix). Figure 4.1 shows details of the operation of an atom gun. An inert gas is normally used for bombardment because it does not produce unwanted secondary species in the primary beam and avoids contaminating the gun and mass spectrometer. Helium, argon, and xenon have been used commonly, but the higher mass atoms are preferred for maximum yield of secondary ions. 

Milk may be a carrier of diseases from animals or from other sources to humans. To avoid contamination before pasteurization, healthy animals should be separated from sick animals or those with infected udders. The animals should be clean, kept in clean housing with clean air, and handled by workers and equipment under strictly sanitary conditions. Post-pasteurization contamination can occur as a result of improper handling, due to exposure to contaminated air, improperly sanitized equipment, or an infected worker. 

Nuclear utiUties have sharply reduced the volume of low level radioactive waste over the years. In addition to treating wastes, utiUties avoid contamination of bulk material by limiting the contact with radioactive materials. Decontamination of used equipment and materials is also carried out. For example, lead used for shielding can be successfully decontaminated and recycled using an abrasive mixture of low pressure air, water, and alumina. 

The implanted ion can be singly or multiply charged and can be any isotope. The mass separation system is used to avoid contamination. As an example, when implanting silicon the isotope is often used instead of to avoid contamination from the signals. After mass... 

A number of techniques have been developed for the trace analysis of siUcones in environmental samples. In these analyses, care must be taken to avoid contamination of the samples because of the ubiquitous presence of siUcones, particularly in a laboratory environment. Depending on the method of detection, interference from inorganic siUcate can also be problematic, hence nonsiUca-based vessels are often used in these deterrninations. SiUcones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and tetrahydrofuran (THF)... 

Cotton yam is dyed in package machines and the dye exhausted by increasing the temperature and adding salt. The dye must be completely dissolved when preparing the dyebaths to avoid contamination with undissolved dye in the yam package. The increased avaUabUity of the prereduced Hquid dyes and the improved quaHty of sodium sulfide have reduced this problem. Incorrectly dissolved dye was previously the cause of most faulty dyeings. 

The precursor fiber is subsequently washed and stretched to the low tex (denier) required for carbon fiber processing. Stretching also imparts considerable orientation to the polymer molecules and provides the basis for the highly oriented carbon stmcture that forms after carbonization. Special care is taken to avoid contamination or impurities that may form strength reducing flaws in the carbon fiber. 

The exhaust gases are generally discharged into dust and fume knockdown equipment to avoid contamination of the atmosphere. Gas-cleaning equipment includes cyclones, setthng chambers, scrubbing towers, and electrical precipitators. Heat-recoveiy devices are utilized both within and outside the lain. These result in an increase in lain capacity or a decrease in fuel consumption. Waste-heat boilers, grates, coil systems, and chains are used for this purpose. 

Regardless of the location of the protein and its state, cell separation needs to be inexpensive, simple, and reliable, as large amounts of fermentation-broth dilute in the desired product may be nandled. The objectives are to obtain a well-clarified supernatant and solids of maximum diyness, avoiding contamination by using a contained operation. Mechanical methods, almost exclusively centrifugation and... 

Precautions must be taken to ensure good electrical contact with the specimen, to avoid contamination of the solution with easily reducible metal ions, and to ensure that inhibitor decomposition has not occurred. Instead of using 2 mL of any proprietaiy inhibitor, 0.5 g/L of inhibitors such as diorthotolyl thiourea or qmuonne ethiodide can be used. 

Sodium wire and finely sliced sodium are equally good to use in this reaction. It is important to avoid contamination of the sodium by surface action which converts part of it into sodium hydroxide. 

The use of more than 1.2 equiv of allyltrimethylsilane is essential for shortening the reaction time as well as to avoid contamination of the product by unreacted benzalacetone. 

Tanks for the transport of chemicals cannot usually be cathodically protected because of the danger of impurities contaminating the cargo. Particular emphasis is placed on the quality of the coating to avoid contamination by corrosion products. 

Figure 14-9 also shows a flowchart for analysis of wet and dry precipitation. The process involves weight determinations, followed by pH and conductivity measurements, and finally chemical analysis for anions and cations. The pH measurements are made with a well-calibrated pH meter, with extreme care taken to avoid contaminating the sample. The metal ions Ca, Mg, Na, and are determined by flame photometry, which involves absorption of radiation by metal ions in a hot flame. Ammorda and the anions Cl, S04 , NO3 , and P04 are measured by automated colorimetric techniques. 

See 2-3.1. Typical laboratory conductivity meters have insufficient sensitivity to measure semiconductive and nonconductive liquids, in Appendix B, some tabulated conductivities appear as < suggesting that the instmment used was inappropriate. Some liquids listed as conductive might fall instead into the semiconductive category (e.g., cymene). Eor conductivities less than 100 pS/m especially, highly sensitive picoammeters are required to measure the small currents involved and great care is needed to avoid contamination of both the sample and the test cell. Several ASTM methods are available according to the conductivity range involved [143-146]. 

Rest facilities should be provided in readily accessible places. To avoid contamination of food, or accidental ingestion of chemicals, these should include facilities to eat meals in a separate location. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Avoid contamination with combustible materials, various inorganic and organic acids, alkalies, alcohols, amines, easily oxidizable materials such as ethers, or materials used as accelerators in polymerizations reactions Stability During Transport Extremely explosion-sensitive to shock, heat and friction. Self-reactive Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent inhibitor of Polymerization Not pertinent. 

Is containment of production processes possible, to avoid contaminants and heat being released to the room air ... 

Often, it is essential that crystals are not damaged unduly by the drying operation. And in the case of food and pharmaceutical grade materials, care should be taken to avoid contamination and powder leakage via dust formation. 

In some cases, it may be desirable to specify an all stainless steel arrester to avoid contamination of the stored liqnid by mst or other particles from the honsing. Note that certain metals may catalyze polymerization of vapors in gas streams containing monomers, which will then be deposited on the flame arrester elements and hasten blockage. Also note that mst may be transported to the flame arrester from npstream sonrces. 

Atomic power production The necessity for avoiding contamination of operative liquids, together with other requirements which must be met in selecting constructional materials in this highly specialised field has resulted in the choice of austenitic steels for applications in heat exchangers, pressure vessels, pipelines and fuel processing. 

The individual characteristics and uses of the basic grades of the austenitic irons are given in Table 3.55. The major uses for these materials occur in the handling of fluids in the chemical and petroleum industries and also in the power industry and in many marine applications. The austenitic irons are also used in the food, soap and plastics industries where low corrosion rates are essential in order to avoid contamination of the product. Ni-Resist grades Type 2, 3 or 4 are generally used for such applications but the highly alloyed Type 4 Ni-Resist is preferred where low product contamination is of prime importance. 

Many chemical-plant vessels constructed of mild steel, copper, or other base metals may be protected from corrosive attack by their contents by means of a lining of one of the noble metals. This form of construction utilises the higher strength of the base metal —as, for example, in the walls of pressure vessels — and at the same time a minimum amount of a much more expensive noble metal is used. The use of noble metals in plant is frequently determined by the desire to avoid contamination of valuable reactants or substances by the products of corrosion of base metals. 

---