WO2008145457A1

WO2008145457A1 - Improved capillary column for gas chromatography

Info

Publication number: WO2008145457A1
Application number: PCT/EP2008/054807
Authority: WO
Inventors: Mario Galli; Stefano Galli
Original assignee: Dani Instruments S.P.A.
Priority date: 2007-06-01
Filing date: 2008-04-21
Publication date: 2008-12-04
Also published as: ITVE20070034A1

Abstract

An improved capillary column for gas chromatography, characterised by consisting of a single capillary tube (2) presenting at least two stationary phases (4, 6) of different characteristics, mutually distinct along said tube.

Description

IMPROVED CAPILLARY COLUMN FOR GAS CHROMATOGRAPHY

The present invention relates to an improved capillary column for gas chromatography.

Gas chromatography (GC) is that particular form of chromatography used for chemical analysis and separation of relatively volatile liquid or gaseous components, known to be applied in various sectors, such as the environmental, pharmaceutical, petrochemical, perfume and fragrance sectors.

Traditional gas chromatography is also known to be used for analysis and separation (total or partial) of a mixture of components flowing within an inert carrier gas (generally helium, hydrogen or nitrogen), via a chromatography column containing a stationary phase.

The different interaction with the column stationary phase by the different components of the mixture to be analyzed leads to the separation of the mixture components, at the column outlet a detection system recording each corresponding element by means of analog or digital electrical signals.

The instrument used for gas chromatography consists of a gas chromatograph, the main components of which are the sample introduction system, the heated chamber containing the column, and the detection system. Gas chromatography currently uses capillary columns consisting of a fused silica, metal, glass or other material tube of very small inner diameter (typically from 0.05 mm to 0.53 mm), on the inner surface of which a constant thickness film of polymer material is deposited, to form the stationary phase. This thickness is generally between 0.05 μm and 5 μm depending on the column type, and is constant throughout the length of the column. As the different mixture components have different affinities with the specific stationary phase of the column, they travel within the tube at different velocities, for which reason they can be separated along the gas chromatography column. The chemical composition of the stationary phase, consisting as stated of a film formed with a uniform thickness throughout the entire column length, determines the types of components which can be separated by the gas chromatography column. Typical components of stationary phases are OV-1 , SE-1 (silicone based) or Carbowax 2OM (polyethyleneglycol based). Generally the stationary phase hence depends on the substances to be analyzed and separated, on their chemical nature and in particular their volatility and polarity.

Notwithstanding the large number of currently available stationary phases, chromatography columns are limited in their use, as each column contains a single stationary phase with a constant thickness along the column, this limiting the column separation capacity to the physico-chemical properties of the single stationary phase which interacts with the mixture to be analyzed. Because of this the use of mixed stationary phases is widespread, these consisting of mixtures of two or more stationary phases with mutually different separation characteristics. A single chromatography column is treated with these mixtures to obtain different separation properties, which in some cases are better than those obtainable with a pure stationary phase.

It has already been proposed to connect in series two or more columns presenting different separation characteristics. This has enabled a method to be implemented derived from gas chromatography (GC) and known as 2DGC (two-dimension gas chromatography), which has offered enormous advantages in terms of separation.

However the series connection of two columns and in particular of two capillary tubes has created a series of drawbacks essentially linked to the fact that it is generally formed using class connectors, which not only potentially but also effectively represent a leakage point for the gas flowing through the column. This not only affects the analysis but also makes it very difficult to reproduce it under the same conditions when a column piece or the connected column assembly is replaced. This drawback, which poses serious and real analysis repeatability problems, is multiplied if several connections are required.

Another drawback consists of the fact that when the glass connectors are subjected to thermal and mechanical stresses (due for example to the modulation systems applied to the 2DGC), the handling of the connected columns becomes problematic and can lead to their mutual disconnection. This sudden disconnection can itself have serious drawbacks both from the analytical and instrumental viewpoints. In particular, a column which no longer receives carrier gas and is at high temperature can easily degrade and irremediably lose its separative capacity, and likewise any mass spectrometer coupled to the gas chromatograph in the GC-MS method can be seriously damaged if it no longer receives carrier gas.

According to the invention, all these drawbacks are eliminated by an improved capillary column for gas chromatography, as described in claim 1 .

A preferred embodiment of the present invention is further clarified hereinafter with reference to the accompanying drawing, showing a schematic longitudinal section through a portion of a gas chromatography column according to the invention.

As can be seen from the figure, the gas chromatography column of the invention comprises a single continuous capillary tube 2 made of fused silica, metal or other material, in which two or more separate stationary phases 4, 6 of different nature and/or different thicknesses are deposited. The invention also includes all possible stationary phase combinations, i.e. stationary phases of different substances or of the same substance but of different thicknesses, or different substances of different thicknesses. These can be positioned one following the other without discontinuities, or can be separated by a portion of column 2 without stationary phases.

By using a single column, and hence by eliminating connections between columns, numerous advantages are obtained, and in particular:

- constructional complications in making the connections are eliminated, - the dangers linked to the risks of carrier gas leakage are eliminated,

- absolute analysis repeatability following column change is ensured,

- those risks linked to system fragility which arise both when connections are made and when using several connected columns subjected to thermal and mechanical stresses are eliminated. It should also be noted that from the analytical viewpoint the use of stationary phases of different nature disposed in series is profoundly different from the use of a mixed phase, i.e. of a mixture of two or more stationary phases, in that the use of phases in series within a column is equivalent to subjecting the sample to be analyzed to a plurality of different chromatographic processes during a single analysis through a single capillary column, this never having been achieved in the past. The method for filling a single column with several stationary phases, possibly of different thicknesses, is traditional and does not constitute an aspect of the invention.

In a variant, not shown in the drawings, the capillary column consists of two separate portions of different outer diameter, each of which presents one stationary phase, the two stationary phases being of different substances and/or thicknesses, as in the preceding example.

Claims

C L A I M S

1 . An improved capillary column for gas chromatography, characterised by consisting of a single capillary tube (2) presenting at least two stationary phases (4, 6) of different characteristics, mutually distinct along said tube.

2. A gas chromatography column as claimed in claim 1 , characterised in that the stationary phases (4, 6) are of different nature.

3. A gas chromatography column as claimed in claim 1 , characterised in that the stationary phases (4, 6) are of different thickness.

4. A gas chromatography column as claimed in claim 1 , characterised in that the single continuous capillary tube presents different inner diameters along its length.

5. A gas chromatography column as claimed in claim 1 , characterised in that the stationary phases (4, 6) are disposed in continuity within the capillary tube (2).

6. A gas chromatography column as claimed in claim 1 , characterised in that the stationary phases (4, 6) are spaced apart by a portion of capillary tube (2) without stationary phases.