Purification approaches

E. coli) and /3-iV-acetylhexosaminidase (A. oryzae), and thus a facile separation and purification approach could be established [78]. 

Purification of feeds. Reducing the concentration of impurities in the feed usually leads to reduced side reactions and less waste formation. This approach can also reduce the need for purges and vent streams. Feed impurities also often lead to degradation of solvents and catalysts. Care must be taken to select a purification approach that does not itself lead to more waste formation. 

Plutonium Purification. The same purification approach is used for plutonium separated from sediments or seawater. In case reduction may have occurred, the plutonium is oxidized to the quadrivalent state with either hydrogen peroxide or sodium nitrite and adsorbed on an anion exchange resin from 8M nitric acid as the nitrate complex. Americium, curium, transcurium elements, and lanthanides pass through this column unadsorbed and are collected for subsequent radiochemical purification. Thorium is also adsorbed on this column and is eluted with 12M hydrochloric acid. Plutonium is then eluted from the column with 12M hydrochloric acid containing ammonium iodide to reduce plutonium to the non-adsorbed tervalent state. For seawater samples, adequate cleanup from natural-series isotopes is obtained with this single column step so the plutonium fraction is electroplated on a stainless steel plate and stored for a-spectrometry measurement. Further purification, especially from thorium, is usually needed for sediment samples. Two additional column cycles of this type using fresh resin are usually required to reduce the thorium content of the separated plutonium fraction to insignificant levels. 

Two-Stage catalytic exhaust purification approached these auto emission problems in a different way. Here the first stage of control, NOx reduction, is achieved catalytically using the reserve chemical reducing capacity of the residual hydrocarbons and carbon monoxide already present in the exhaust (Fig. 3.2b e.g., Eqs. 3.5-3.8). 

The techniques are more flexible and require less detailed planning of the Intended experiment, allowing the experimenter to change the purification approach relatively easily. 

Further modifications of the ELR-base protein purification approach have been made in order to circumvent some problems related to protein purification when the protein is expressed at ultra-low levels. One of the multiple factors that influence thermosensitive behavior is polymer concentration. Some proteins, and their respective fusion proteins, have the drawback of being expressed at low levels, which have repercussions on inverse transition cycling efficiency. To overcome this problem, the addition of free ELR to the soluble lysate containing the fusion protein has been proposed [126, 132, 133]. Free ELR acts as a co-aggregant that leads not only to a decrease in T, due to the increase in ELR concentration but also to an easier recovery of aggregates thanks to their large size. This ITC variant focused on the addition of excess ELR has allowed the purification of ultra-low concentration ELR fusion constructs, with several such examples having been reported [126, 132, 133]. 

Be aware of the flow needs of the gas generator(s) that you will be using. With air generators there is an almost 1-1 ratio of incoming gas flow to product gas there is almost no flow loss. However, with nitrogen generators this is not the case. Most of these units, independent of the purification approach (semiper-meable membrane or contaminant adsorption) require large quantities of input air to produce the desired output flow. 

Fig. 3 Classical purification approaches. In this strategf, the desired enzyme is purified by traditional biochemical chromatography, and protein sequence information is used to isolate the desired gene from plant cDNA...

After the wide realization of the cost effectiveness of this purification approach, chromatography has recently become the preferred method for rapidly accessing products of high added value, such as enantiomers. In a drug discovery and development context, enantioselec-tive chromatography is applicable both in the early stages of development of a drug, when the two enantiomers are required, and as the final purification step of synthetic enantioselective processes. 

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