Inherent contaminants

For wettability at water content 97%, polar functional groups are either interspersed along the bonded phase backbone or used as end capping agents. Be sure to read the manufacturer s literature carefully in order to confirm this and determine whether any special considerations need to be taken into account. 

One of the most difficult problems any manufacturer of high-purity solvents faces is the variability of the raw material stock used in solvent production. Solvent raw materials can be generated in many ways, including production via fractionation of large-scale distillations, as by-products of petroleum cracking processes, and as a result of synthetic processes or by-products thereof [37]. 

Each production method will introduce vastly different levels and types of impurities. As an example, consider the solvent methyl r-butyl ether (MrBE). When it is the product of a petroleum-based source, numerous ethers, aldehydes, ketones, and alcohols are typically present. Synthesis of MrBE from methanol and isobutylene reduces the potential contaminant range to residual methanol and isobutylene and alcoholic contaminants in the methanol and alkene contaminants in the isobutylene. The suitability of either source of M/BE for final analytical use depends strictly on the requirement of the end user. 

More important, from an end user point of view, is the subtle variability of the raw material over time and the resultant effects on the finished high-purity solvent 

Review of common and uncommon contaminants in high-purity solvents is b ond the scope of this section. The inqrortant point here is that the presence of a contaminant in a high-purity solvent is often totally unexpected and unanticipated by both the manufacturer and the end user. One must realize that it is impossible for any manufacturer to develop tests and specifications for unanticipated contaminants in the raw materials. It should be emphasized that feedback from end users to a manufacturer is critical. Feedback makes a manufacturer aware of problems that may then be addressed and eliminated in the future. 

---

New water may come from a number of sources (Table 3) and the degree of inherent contamination will vary accordingly. 

In addition to the urgent problem of capacity, manufacturers have to cope with the operating costs of production, which are increased by the need for skilled personnel and expensive media components. Another cost driver is the inherent contamination risk when using mammalian cell culture systems. All materials must be checked closely for bacterial and viral contamination, and the presence of prions and endotoxins. This affects not only the manufacturing process, but also downstream materials and even human semm albumin (HSA) used for formulations. In the end, production costs add up to 100-1000 per gram of therapeutic protein. 

Vaporization of the HN3 can be avoided by selecting acids that have insoluble sodium or potassium salts, and the hydrazoic acid is then separated by filtration. This procedure is safer than the distillation methods however, purity is sacrificed as the product is inherently contaminated. A number of reaction mixtures have been recommended [49], (Table IV). With the first reactant... 

Contamination control presents some unique challenges to the ECM manufacturer while others are much the same. A review of common issues with emphasis on ECMs is discussed here. There are two primary sources of contamination (1) inherent contaminants in the tissue and (2) introduced contaminants. Introduced contaminants include those introduced intentionally (processing chemicals) and unintentionally (environmental contaminants). 

Inherent contaminants are not normally considered contaminants. The removal of undesirable tissue components such as cells, cell walls, antigens, and DNA are the very reason some medical device companies exist. Each has a (usually) proprietary method for removing the non-ECM components from tissue. For the medical device manufacturer this is an unusual problem because raw materials are otherwise built to specifications that include limits on contaminants. Technologies for ranoving tissue components are not discussed in this chapter. 

Disposable steel needles used widely in medical practice for drawing of blood samples cannot be used for sampling blood intended for trace metal analysis. Contamination of blood samples by such needles can exceed the actual level of chromium in the sample by a factor of 100-1000. In case liquid chromatography (LC) is used for separation of species, the system inherent contamination has to be taken in account, when using high-performance liquid chromatography (HPLC) equipment (pumps, valves, columns, capillaries) made from stainless steel. 

Various chlorinating agents have been used to convert carboxylic acids or their anhydrides into acid chlorides. The most commonly reported methods employ thi-onyl chloride, phosphorus trichloride, or phosphorus pentachloride. However, the unsatisfactory degree of purity of the final acid chlorides, due to inherent contamination with sulfur or phosphorus by-products, has stimulated a search for new reagents and catalysts. 

Drums and containers. Containers used for the transport of polymer dispersions will include small kegs, drums, intermediate bulk containers (one-way or reusable), in-situ or demountable road containers and road and rail tankers. If a sterile emulsion is filled into a sterile, impervious container, microbial growth will not occur but this is very seldom the case and it is often only the biocide that prevents inherent contamination from causing infection. 

The problems inherent to these two processes are not only the production of corrosive salts, but also the possibiUty of product contamination by 2-chloroethylamine [689-98-5] as starting material or intermediate. This substance can initiate polymerisation of ethyleneimine with the elimination of HCl. 

Pure diketene is stable for several weeks if stored at or below 0°C in an aluminum or stainless steel container. Glass should be avoided because of its inherent basicity which favors slow polymerization. Above 15°C slow decomposition occurs and the color becomes progressively darker. Pressure buHd-up Upon prolonged exposure to heat is possible. Heating and contamination of the container, especiaHy by acids, bases, and water, should be avoided. Residual vapors in empty containers are hazardous and may explode on ignition. 

Chemical Hazards. Chemical manufacturers and employees contend with various ha2ards inherent ia productioa of evea commonplace materials. For example, some catalysts used ia the manufacture of polyethylene (see Olefin polymers) ignite when exposed to air or explode if allowed to become too warm the basic ingredient ia fluorocarboa polymers, eg, Tefloa (see Fluorine compounds, organic), can become violently self-reactive if overheated or contaminated with caustic substances (45,46) one of the raw materials for the manufacture of acryflc fibers (see Fibers, acrylic) is the highly toxic hydrogen cyanide (see Cyanides). 

Open-loop systems have inherently long residence times which may be detrimental if the retentate is susceptible to degradation by shear or microbiological contamination. A feed-bleed or closed-loop configuration is a one-stage continuous membrane system. At steady state, the upstream... 

Pump and treat technology is inherently slow because it depends on ground water for transport of the contaminant to the extraction well. This characteristic is particularly troublesome when the contaminant is only slightly water soluble, adheres to the soil, or collects ia pools within the aquifer. 

In general, low level detection is masked by the noise level inherent in any measuring device. Electrochemical methods are susceptible to electrical interference from external sources, variations in reference electrode parameters resulting from aging or contamination, and interference from redox... 

The inherent solderabiUties of selected alloys are Hsted in Table 9. Class IV and V ratings with this particular flux indicate the presence of oxides or other surface contaminants that may be removable with more aggressive flux or acid pickling. 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

Another aspect of cost reduction would be solvent economy. The need to preferentially select inexpensive solvents and employ the minimum amount of solvent per analysis would be the third performance criteria. Finally, to conserve sample and to have the capability of determining trace contaminants, the fourth criterion would be that the combination of column and detector should provide the maximum possible mass sensitivity and, thus, the minimum amount of sample. The performance criteria are summarized in Table 1. Certain operating limits are inherent in any analytical instrument and these limits will vary with the purpose for which the instrument was designed. For example, the preparative chromatograph will have very different operating characteristics from those of the analytical chromatograph. 

Another important application area for PSAs in the electronic industry focuses on the manufacturing, transport and assembly of electronic components into larger devices, such as computer disk drives. Due to the sensitivity of these components, contamination with adhesive residue, its outgassing products, or residue transferred from any liners used, needs to be avoided. Cleanliness of the whole tape construction becomes very critical, because residuals like metal ions, surfactants, halogens, silicones, and the like can cause product failures of the electronic component or product. Due to their inherent tackiness, acrylic PSAs are very attractive for this type of application. Other PSAs can be used as well, but particular attention has to be given to the choice of tackifier or other additives needed in the PSA formulation. The choice of release liner also becomes very critical because of the concern about silicone transfer to the adhesive, which may eventually contaminate the electronic part. 

---