Development Of Purification Techniques Research Articles

Too big to bind? Will the purification of large and complex therapeutic targets spell the beginning of the end for column chromatography?

Progress in some areas of medical research is leading to larger and more complex therapeutic products—for example, cellular or gene therapies. For decades, the bioprocessing industry has relied upon column chromatography as the mainstay of purification processes. Whilst highly effective for the purification of proteins and smaller molecules, chromatographic techniques are not necessarily well suited to purification of these newer, larger targets. This article considers the approaches adopted in the purification of large, complex targets and emphasises the need for more focused development of purification techniques more suited to the target's size and complexity. Copyright © 2008 Society of Chemical Industry

Protocol for the characterization of single-wall carbon nanotube material quality

Single wall carbon nanotubes (SWCNTs) can be synthesized and purified by a number of techniques, and always contain certain amount of impurities of varying composition (mostly metal catalyst and non-tubular carbon), as well as defects resulting from purification. Particular purification route also affects homogeneity of nanotube material and its dispersability in organic solvents, which are important in the subsequent application development. A number of analytical characterization tools have been used successfully in the past years to access various properties of nanotube materials, but lack of standards makes it difficult to compare these measurements across the board. In this work we report on the protocol which standardizes measurements in TEM, SEM, TGA, Raman and UV–VIS spectrometer, consumes <30 mg of material, and was found to provide fast and reliable feedback in the development of purification techniques. The amount of residual metal catalyst is determined directly, and numerical measures are established for parameters such as homogeneity, thermal stability and dispersability, to allow easy comparison of SWCNT materials. Quantitative measurement of non-tubular carbon impurities still remains a problem, and we have to rely on qualitative electron microscopy observations.

Hydrogen sorption properties of arc generated single-wall carbon nanotubes

Studies regarding the possible use of single-wall carbon nanotubes (SWNTs) as a hydrogen storage material have attracted considerable interest in the last years. However, a large discrepancy in the results reported by different scientific groups is evident, and many of the recent studies do not confirm superior H2 adsorbing properties of SWNTs compared to more conventional carbon materials. Nevertheless, synthesis of SWNTs with different diameters and a development of techniques for purification and opening can contribute to the improvement of their H storage efficiency. In the present work, SWNTs were produced by arc evaporation of graphite electrodes with the use of two different catalysts, 3Co/Ni and YNi2. A three-step purification technique allowed enrichment of the samples with SWNTs reaching a level of purity exceeding 75%. In carefully performed sorption experiments on purified samples, reversible storage capacity of 2.4 wt.% H2 was observed at cryogenic temperatures below −150°C and at a pressure of 25 bar H2. Thermal desorption studies revealed the presence of weakly bonded physisorbed hydrogen (90%) and chemically bonded hydrogen (10%). The latter was released at temperatures above 450°C as a result of breaking of the covalent C–H bonds.

Development of techniques for purification of waste waters: removal of pyridine from aqueous solution by adsorption at high-area C-cloth electrodes using in situ optical spectrometry

The adsorption and electrosorption/desorption behavior of pyridine (Py) was studied for potential applications to the purification of industrial waste-waters. The use of high-area carbon cloth (C-cloth) electrodes as quasi-3-dimensional interfaces, coupled with in situ UV–Vis spectrophotometric techniques and scanning kinetics for quantitatively monitoring the adsorption/desorption processes and simultaneously obtaining kinetic parameters are described. The conversion of Py to PyH +, which decreases the removal efficiency, takes place in non-buffered electrolyte solution due to pH changes but is eliminated in a HOAc+NaOAc buffer (pH 6.8) solution. Rapid and complete removal of Py is then achieved by anodic polarization. Under controlled potential, Py removal rates are lower than those for galvanostatic polarization where changes of potential arise due to double-layer charging.