Method for fluorinating a filter for a pipette tip, pipette tip, associated production method and pipette

Abstract

A method for fluorinating a filter for a pipette tip, the filter being made of a solid porous structure made of polyolefin. The method comprises the following steps: (a) placing the filter in an enclosure, (b) creating a vacuum in the enclosure, and (c) bringing the filter into contact with a fluorination agent injected into the enclosure in a gaseous state, the fluorination agent being made up of difluorine F.sub.2, the difluorine F.sub.2 being injected into the enclosure at a partial pressure between 100 Pa and 10000 Pa and step (c) being done at a temperature between 0? C. and 100? C. A pipette tip comprising a filter modified by the fluorination method, a method for producing such a tip, as well as a withdrawing pipette equipped with such a tip.

Claims

1. Method for fluorinating a filter for a pipette tip, this filter being formed by a porous solid polyolefin structure, characterized in that it comprises the following steps: (a) placing the filter in an enclosure, (b) creating a vacuum in the enclosure, and (c) contacting the filter with a fluorination agent introduced in the gaseous state into the enclosure, in that the fluorination agent consists of difluorine F.sub.2, in that the difluorine F.sub.2 is introduced into the enclosure at a partial pressure between 100 Pa and 10000 Pa, in that step (c) is conducted at a temperature between 0? C. and 100? C., and further comprising after step (c): (e.sub.1) creating a vacuum in the enclosure, followed by (e.sub.2) contacting the filter with dihydrogen or a mixture comprising dihydrogen, the dihydrogen or mixture comprising dihydrogen comprising dihydrogen being introduced in the gaseous state into the enclosure.

2. Fluorination method according to claim 1, wherein the polyolefin is chosen from a polyethylene and a polypropylene.

3. Fluorination method according to claim 2, wherein the polyolefin is polyethylene.

4. Fluorination method according to claim 1, wherein the difluorine F.sub.2 is introduced into the enclosure at a partial pressure between 500 Pa and 8000 Pa.

5. Fluorination method according to claim 1, wherein step (c) is conducted at a temperature between 10? C. and 60? C.

6. Fluorination method according to claim 1, wherein step (c) is carried out for a duration between 1 min and 60 min.

7. Fluorination method according to claim 1, wherein, during step (c), a number of moles of difluorine greater than or equal to the equivalent number of moles of hydrogen atoms of the polyolefin is introduced.

8. Fluorination method according to claim 1, wherein the mixture comprises dihydrogen and nitrogen.

9. Fluorination method according to claim 8, wherein the volume percentage of dihydrogen in this mixture is greater than or equal to 2% vol.

10. Fluorination method according to claim 1, wherein, during step (e.sub.2), a number of moles of dihydrogen less than or equal to the number of moles of difluorine introduced during step (c) is introduced.

11. Fluorination method according to claim 1, wherein step (e.sub.2) is carried out for a duration between 10 min and 2 h.

12. Fluorination method according to claim 1, wherein step (e.sub.2) is conducted at a temperature between 0? C. and 200? C.

13. Fluorination method according to claim 1, wherein, during steps (b) and (e.sub.1), the pressure in the enclosure is less than or equal to 100 Pa.

14. Fluorination method according to claim 1, wherein step (c) is monitored by infrared spectroscopy.

15. Fluorination method according to claim 14, wherein step (c) is stopped when this ratio ACH.sub.2/ACF.sub.x reaches a value less than or equal to 15.

16. Fluorination method according to claim 14, wherein step (c) is monitored by tracking the evolution of the ratio ACH.sub.2/ACF.sub.x of the area of the infrared vibration bands corresponding to the CH.sub.2 groups over the sum of the areas of the infrared vibration bands corresponding to the CHF groups and to the CF.sub.2 groups.

17. Method for producing a pipette tip comprising a fluorinated filter, the method comprising the following steps: (i) providing a filter formed by a porous solid polyolefin structure, (ii) fitting the filter in the pipette tip, and (iii) fluorinating the filter by implementing the fluorination method according to claim 1.

18. Fluorination method according to claim 1, further comprising a step (d) of removing the by-products formed during step (c), steps (e.sub.1) and (e.sub.2) being performed after step (d).

19. Fluorination method according to claim 18, wherein step (d) is carried out by degassing the by-products during step (c).

20. Fluorination method according to claim 19, wherein step (d) is carried out by vacuum degassing the by-products formed during step (c).

21. Fluorination method according to claim 18, wherein steps (c) and (d) are carried out successively, step (d) of removing the by-products being carried out at the end of step (c).

22. Fluorination method according to claim 18, wherein step (d) is carried out by chemical trapping of the by-products formed during step (c).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic elevation and exploded representation of a sampling pipette at the end of which a pipette tip according to the invention is intended to be fitted.

(2) FIG. 2 is a schematic cross-sectional representation of the pipette tip represented in FIG. 1.

(3) FIG. 3A illustrates the absorbance spectra conveying the evolution of the absorbance (denoted A and expressed without units) as a function of the wavenumber (denoted v and expressed in cm.sup.?1) as obtained, with the implementation of the method for fluorinating a pipette tip filter according to the invention, this method being carried out at three different partial difluorine pressure values.

(4) FIG. 3B is an enlargement of the total area, denoted A.sub.CF.sub.x, corresponding to the sum of the area of the infrared vibration bands corresponding to the CHF groups and of the area of the infrared vibration bands corresponding to the CF.sub.2 groups.

(5) FIG. 4 illustrates the evolution of a drop of water deposited on two polyethylene filters, one not treated (FIG. 4A) and the other treated with the fluorination method according to the invention (FIG. 4B), over a duration of 5 min.

(6) It is specified that the common elements in FIGS. 1 and 2 are identified with the same reference number.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(7) In FIG. 1, a sampling pipette 10 intended to receive a pipette tip 20 according to the invention has been represented. This sampling pipette 10 may particularly be an air-displacement, manual or motorized pipette.

(8) This pipette 10 comprises an upper part forming a handle 12 and a lower part 14 intended to receive a tip, or cone, 20 of pipette represented in a longitudinal cross-section in FIG. 2.

(9) In the representation in FIG. 1, a single tip 20 is intended to be attached to the sampling pipette 10, known as a single-channel pipette.

(10) Obviously, there is nothing preventing envisaging that several tips may be simultaneously attached to a so-called multi-channel sampling pipette (not shown).

(11) With reference to FIG. 2, it is observed that the tip 20 has a tapered shape, which retracts from the upper part 22 thereof to the lower part 24 thereof which corresponds to the part of the tip 20 which is intended to be immersed in the solution to be sampled.

(12) The tip 20 is conventionally made of polyolefin and, more particularly, of polypropylene.

(13) The tip 20 comprises, in the upper part 22 thereof, a radially disposed filter 26. This filter 26 is formed by a porous solid polyolefin structure, preferably made of polyethylene.

(14) This filter 26 has enhanced hydrophobic properties, obtained thanks to the implementation of the fluorination method according to the invention.

(15) The fluorination method according to the invention was conducted under the following operating conditions.

(16) Polyethylene filters were placed in an enclosure. After closing the enclosure, a vacuum of the order of 10 Pa was successively produced, in the same enclosure, before introducing difluorine therein, at different partial pressures, in this instance at 1000 Pa, at 3000 Pa and at 5000 Pa.

(17) The fluorination reactions were conducted at ambient temperature, typically at 20? C., and were monitored by infrared spectroscopy.

(18) Reference may be made to FIG. 3A which illustrates the absorbance spectra as obtained, after contacting the filter with difluorine for 30 min, according to the partial difluorine pressure applied.

(19) In FIG. 3A, the infrared vibration bands corresponding to the CH.sub.2 groups are situated in a wavenumber range between 3000 cm.sup.?1 and 2600 cm.sup.?1 whereas the infrared vibration bands corresponding to the CHF and CF.sub.2 groups are situated in a wavenumber range between 1300 cm.sup.?1 and 900 cm.sup.?1.

(20) Table 1 below shows the ratio, denoted A.sub.CH.sub.2/A.sub.CF.sub.x, between: the area of the infrared vibration bands corresponding to the CH.sub.2 groups, denoted A.sub.CH.sub.2 in FIG. 3A, and the sum of the areas of the infrared vibration bands corresponding to the CHF and CF.sub.2 groups, denoted A.sub.CF.sub.x in FIGS. 3A and 3B.

(21) TABLE-US-00001 TABLE 1 Partial difluorine pressure applied (Pa) A.sub.CH.sub.2/A.sub.CF.sub.x 5000 2.63 3000 5.38 1000 12.0

(22) It is observed that, for the same contacting duration, a replacement rate of hydrogen atoms by fluorine atoms that increases as the partial difluorine pressure increases is obtained.

(23) FIG. 4 illustrates the behavior of a drop of water deposited on the surface of two polyethylene filters, the first filter not having been treated (FIG. 4A) and the second filter having been treated by the fluorination method according to the invention described above with reference to FIGS. 3A and 3B and implemented at the partial difluorine pressure of 3000 Pa (FIG. 4B).

(24) With reference to FIG. 4A, it is observed that the contact angle ?, which is of the order of 90? when the drop of water is deposited, declines over time, meaning that the outer surface of the untreated polyethylene filter displays wettability properties and, hence, water penetrates inside the porous structure of this filter under the influence of its own weight.

(25) Conversely, in FIG. 4B, it is observed that the contact angle ? remains at a value greater than 90? for the 5 min of observation, which means that water does not penetrate into the porosity of the polyethylene filter treated with the fluorination method according to the invention. The fluorinated filter therefore retains the hydrophobic properties thereof over the same duration.

BIBLIOGRAPHY

(26) [1] EP 0 631 817 A1 [2] US 2004/0028890 A1 [3] US 2012/0009100 A1