Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1995-01-20
1997-07-15
Reifsnyder, David A.
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210781, 2103801, 210407, 422 72, 422101, 436177, B01D 2126, B01D 6100
Patent
active
056479905
DESCRIPTION:
BRIEF SUMMARY
This invention relates to centrifuge methods and devices for concentrating macromolecules from a solution.
There has been a number of analytical procedures developed in the biochemical art wherein it is required to remove solvent from e.g. protein solutions in order to have a more concentrated protein sample which can be analysed effectively, or in order to have a protein free filtrate for analysis, or to replace or remove low molecular weight ions or solutes, or to study protein binding attributes of various chemicals in combination with various protein samples. Many other analytical procedures involving not only proteins but macromolecular species in general, have also been developed wherein it is necessary to concentrate a macromolecular component in a liquid sample.
When concentrating small volumes of macromolecules in solution using filtration, e.g. ultrafiltration, there exist the problems of macromolecular binding to the membrane surface and of filtration to dryness. If part of the retentate is adsorbed on the membrane surface the yield of the process will of course decrease and the filtration time will increase due to the decreasing effective membrane area.
In the design of centrifugal filtration devices, the effective membrane area to sample volume to be filtered has been limited by the designs proposed. Low membrane area to volume ratios provide good recovery but low filtration rates. Conversely low volume and large membrane surfaces result in faster filtration but lower recoveries due to the protein binding to the membrane surface.
In the prior art, the centrifugal self-cleaning ultrafilter, described in U.S. Pat. No. 3,488,768, the teachings of which are incorporated herein, is limited due to the large membrane surface area which causes excessive adsorptive loss of the macromolecules.
The initial advantage of a high flow rate through a large filter surface area is rapidly limited as the concentration goes on and the physical surface area is decreasing. The flow rate through the remaining filter area is also reduced by the effect of concentration polarization.
On the other hand, more recent designs such as AMICON MPS-1 Micropartition system (AMICON Publication 472) and the AMICON CENTRICON device described in U.S. Pat. No. 4,632,761 limits membrane surface area to the area at the bottom of the sample reservoir tube, frequently resulting in a poor ratio of membrane surface area to sample volume and extended concentration time.
The dead stop feature which stops the sample concentrating to dryness according to U.S. Pat. No. 4,632,761 is limited by remaining adsorptive losses which result from the concentrated sample remaining on the surface of the membrane and a reduction of effective membrane surface area resulting from this feature.
To recover the retentate from the concentrate pocket a reverse spinning step is used which means that the centrifuge has to be stopped and the sample reservoir with the filtering means and the centrifuge tube have to be taken out from the centrifuge. The different devices are then rearranged and again inserted into the centrifuge now in a way allowing the centrifugal forces to recover the retentate from the pocket at the bottom of the sample reservoir and the surface of the filter. The use of a pipette to recover the retentate from the bottom of the sample reservoir is delicate because the surface of the filter might be damaged by the tip of the pipette. This necessary step to get the final product out of the concentration device is thus complicated and will take a lot of time. Furthermore, a dedicated retentate recovery tube has to be used which increases the costs.
Whilst the reverse spinning feature partially resolves the problem of loss of recovery on the membrane surface, subsequent loss is caused by the adsorption of the concentrated solution on the membrane and reservoir walls of the apparatus during the reverse spinning procedure.
In addition this device requires a specifically designed filtrate collection vessel which is mounted below the sample reservoir--fi
REFERENCES:
patent: 3488768 (1970-01-01), Rigopulos
patent: 3583627 (1971-06-01), Wilson
patent: 4632761 (1986-12-01), Bowers et al.
patent: 4722792 (1988-02-01), Miyagi et al.
patent: 4874516 (1989-10-01), Kondo
patent: 4919860 (1990-04-01), Schindler et al.
Reifsnyder David A.
Stone Mark P.
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