Packed column lifetime

One question of chief interest concerns the number of runs that can be run with one individual SEC column. The lifetime of the sorbent itself must be tested as well as the maximum run number for the packed column. Because column packing procedures for SEC columns are rather time-consuming and all SEC columns have to be checked very carefully with respect to performance, very frequent repacking of the column is unreasonable. Therefore, CIP protocols are generally necessary. The CIP protocol should be developed as part of the process validation program. 

Column. Although the advantage of the normal-phase column is the high resolution in the separation of all tocopherols and tocotrienols, the silica packing material in a normal-phase column is very reactive to strong polar chemicals. Any high-polarity compounds in the sample extract and mobile phase will diminish the column performance and shorten the column lifetime. It is very important to ensure that the sample extract is free of water and metal ions, and it is also advisable to regenerate the column routinely. 

Packed columns are used repeatedly for most biotechnology processes. Regulatory agencies have expressed concern that column performance may deteriorate with continued use. Industry has responded by employing resin lifetime studies at both small and production scales [33], Validation of the ability to produce consistent product for the lifetime of the resin is essential, but there are currently some in industry who believe that small-scale studies extended to the end of... 

The use of these constants is described in the table in the section entitled Properties of Some Liquid Phases for Packed Columns. The viscosity data, where available, are presented in cSt, which is 10 m2/sec. Cross-linked silicone phases based on the silicones are especially valuable for capillary gas chromatography. They are not specifically treated in this table since the differences in many properties are quite often subtle. The cross-linked phases have much longer lifetimes due to the effective immobilization. 

The basic pH of TEAB buffers used with reversed-phase HPLC columns often leads to degradation of column material. We have used Zorbax columns, which contain fully silylated packing material and have a much longer lifetime in TEAB. Although the resolution of these columns seems to be less, most separations are relatively easy and column lifetime is of more importance. 

A restriction to the operation of GC-MS can be caused by solvent peaks. If the solvent injected onto a packed column flows via a separator into the ion source of the mass spectrometer, it results in an unacceptable increase in pressure which causes the built-in pressure protection devices to shut the mass spectrometer down. It also much reduces the lifetime of source components such as filaments and heaters. Therefore a valve is fitted at the end of the column, which allows effluent to be vented to a pump or to tile atmosphere until the solvent has passed. The flow rates associated with the use of capillary coliunns are such that the pressure generated by the solvent is not as great as with a packed column. The total effluent may therefore be passed directly into... 

The columns should be packed with fine particle materials using a high-pressure slurry technique to obtain good efficiency and bed stability. The production of regular efficient HPLC columns becomes more difficult with decreasing size of packing particles. Even when this problem is solved, the column-end frits are more easily blocked by very fine particles, which may be detrimental to the column lifetime. 

Proper column maintenance is very important to ensure optimal performance and extended column lifetimes. There are common procedures that apply to all columns, e.g., avoiding mechanical or thermal shock. There are procedures that are column specific, such as avoiding chloride-containing mobile phases to prevent halide cracking if the column tubing and frits are made of stainless steel (especially at low pH). Nonetheless, columns made with stainless steel tubing and packed with silica-based stationary phases are the most commonly used in HPLC. Thus problems associated with these columns and how to prevent such problems by proper column maintenance will be discussed here. 

The reactions were carried out in isopropyl alcohol. This compound was selected as solvent because the natural lifetime of the aromatic radical anion with respect to protonation (1, 3) is longer than in methyl alcohol or ethyl alcohol. The isopropyl alcohol was obtained from Mathe-son, Coleman, and Bell and was freshly distilled over sodium metal through a glass-packed column for each set of runs. Anthracene from Matheson, Coleman and Bell, pyrene from Aldrich Chemical Co., m-terphenyl and p-terphenyl from City Chemical Corp. were purified as described (2). 9,10-Dimethylanthracene obtained from K and K Laboratories, Plainview, N. Y., was recrystallized from isopropyl alcohol solution. 

The pressure on the pump tubes should be readjusted when the type or number of pump lubes or the flow manifolds are changed. Periodical readjustments should also be made when pump tubes gradually age under usage. Note that pressure adjustments optimized for open ended pump tubes (i.e. without load) may have to be readjusted when the pump tubes are later connected to a manifold, particularly when the flow impedance of the manifold is high, as when packed columns are used in the system. Some operators tend to overtighten the screws to make sure that the flows will not be influenced by a change in impedance. However, this may significantly shorten the lifetime of the pump tubes as well as deteriorate the reproducibility of the flow due to panial or complete adhesion of the inner wails of the pump tubes under excessive pressures. 

Cyclodextrins were introduced as chiral selectors in GC in the 1980s and rapidly became estabhshed as the most powerfiil and versatile materials for GC enantioseparations. The first GC enantioseparation employing CyD as a chiral selector was reported by SybUska s group in 1983 [17]. A packed column was used in this study with a rather short lifetime and rather low peak efficiency. Later Venema and Tol-sma reported enantioseparation with a capillary column which was modified by heptakis(2,3,6-tri-0-methyl)- -CyD (TM- -CyD) [18]. This kind of capillary column... 

If pressure-sensitive soft gels are used and the amount of small particles, so-called fines, is too high, this of course directly influences the field of application (flow rate, column length). In the case of analytical separations, this often does not matter much, because pre-packed columns are mostly used. In the case of preparative purifications, however, a column with a low number of plates and an increased back pressure negatively influences the loading, purity, run time, and lifetime. 

With higher-viscosity solvents, column lifetime decreases (silica packing breaks down mote rapidly) and pump maintenance requirements increase (e.g., piston seals wear faster). These costs are often minimal when conqiared with the savings realized through increased system efficiency and sanqile throughput. A good routine preventive maintenance program is recommended in these cases. 

A discussion of column evaluation may seem inappropriate to biochemists who have traditionally packed gel SEC columns themselves and run them without testing. Such columns would eventually be unpacked when the performance degraded, and the packing material would be cleaned or discarded. The quality of the column was not significant in relationship to the time necessary to evaluate it. HPSEC columns are usually more expensive than their classical counterparts, and consequently, users are concerned about quality assurance, column longevity, sample recovery, and extension of column lifetime. Because there are major differences in columns from different manufacturers, users must have a qualitative basis for column comparison. Columns should also be evaluated periodically during their use so that loss of efficiency can be monitored and columns cleaned, when necessary, to restore resolution. 

Many negative experiments were made to obtain good pre-packed columns, but the lifetime of a pre-packed column in PS-SFC is only a few hours quick rearrangement of particles leaves unacceptable void volumes and the maximum efficiencies ob-... 

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