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CSIC TP010- Coating technique of the inner surface of flexible capillaries and its application for the manufacture of chromatography columns and others.
Institute of Physical-Chemistry Rocasolano of CSIC has developed and patented a novel industrial technique for coating the inner surface of flexible capillaries. The technique finds application, for example, in the manufacture of columns for Gas Chromatography, solid-phase microextraction devices, etc. Our aim is to contact companies involved in the manufacture of analytical instruments and chromatographic columns that might have interest in this particular development.
Specification sheet:
DESCRIPTION

The static method for coating the inner surface of capillaries in the manufacture of columns with application to chromatography, was developed during the decade of 1960. This method consists in filling the capillary with a solution of known concentration of the coating substance and its subsequent evaporation. This is the mothod adopted by the industry because it permits a precise knowledge on the amount of substance that forms the film coating. This knowledge is esential in the case of columns applied to chromatography.

The longest and most problematic step of column manufacture by the static method is the solvent evaporation. Up to now, two techniques have been employed with this purpose:

- By applying vacuum on an open end of the column, while the other end remains sealed (closed end). This is the most usual in the industry.

- By heating at ambient pressure the whole column in a thermostatic bath, applying a "buffer" capillary (a flow restriction) in the open end.

However, these techniques (so-called "current techniques") present the problems we have mentioned previously.

Our technique involves the steps, for a static coating process, of capillary pre-treatments, column filling with the coating solution, evaporation, flush with nitrogen and further thermal stabilization of the column. All steps can be sequentially performed, and electronically controled for automation if desired, in the equipment specially designed for this purpose.

As the evaporation process in the system admits the application of solvents with a high boiling point, it opens a wide spectrum of choices for the selection of the solvent when compared with the traditional static techniques employing vacuum (for example, we use a mixture of Decalin - boiling point 185 ºC - for polyethylene). Of course, incrementing the solvent options is important when cost reducing and environmental criteria are to be apllied. In this respect, an example could be our application of ethanol-water for Carbowax, in place of dichloromethane. Even though, the evaporation can be run at column rates over 7 meters/hour, so it is very fast compared to traditional vacuum procedures using conventional solvents.

The main features of the developed industrial procedure are the following:

1) Admits coating substances thar are only soluble at high temperatures (polyethylene, teflon, etc.)

2) The designed system allows the automation of the industrial process.

3) It is very fast. The column evaporation rate generally exceeds 7 meters/hour, so a 30 meters column can be evaporated in less than 5 hours.

4) It is completely safe. As it does not use vacuum, losses by solvent bumbing due to the expansion of vapor micro-bubbles are not possible. The step for the elimination of micro-bubbles or degassing is unnecessary for the process.

5) Permits the exact knowledge of the column phase-ratio.

The industrial design of the equipment is for 10-20 columns batch, but scaling-up to any number of columns is straightforward and offers no technical problems. Therefore, a business development for the commercialization of the equipment also offers possibilities.

INNOVATIVE ASPECTS

The configuration of the equipment is such that admits thermosetting of the columnfilling step at any temperature required, so polymers or substances which are soluble only at high temperatures in low vapor pressure solvents can also be coated rapidly. Beside the conventional stationary phases, we have been manufacturing polyethylene capillary columns for our specific academic investigation in our lab-scale prototype.

COMPETITIVE ADVANTAGES

But most important is that our technique is much safer; loss by spills due to the growth of bubbles in the coating solution (bumping) is not possible. The phase ratio can be known very accurately with four significant digits. The process control is very simple and full automation is feasible.

KEYWORDS

002003003 Coats and Surface Treatment

008001001 Analyses / Test Facilities and Methods

PATENT

20022752, applied for at 2002-11-29

CONTACT

JOSE MARIA BIELZA DE ORY
email: M.Bielza@orgc.csic.es
phone: +34 915616800 (ext. 3231)

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