WO2002097426A1

WO2002097426A1 - Method for the analysis of a sample by means of capillary gas chromatography, and means for use in such a method

Info

Publication number: WO2002097426A1
Application number: PCT/NL2002/000346
Authority: WO
Inventors: Albert Tangerman
Original assignee: Katholieke Universiteit Nijmegen
Priority date: 2001-05-30
Filing date: 2002-05-30
Publication date: 2002-12-05

Abstract

The present invention relates to a method for analysing a sample for one or more components of interest by means of capillary gas chromatography, in which a sample is introduced in a liner which contains a particulate packaging material that preferably comprises beads, granules or spheres, and which is operably connected to a capillary column, such that when said sample is introduced into the liner, said one or more components pass into the capillary column. The method is particularly suited for the analysis of samples wherein the components of interest are free or esterified fatty acids, preferably underivatized fatty acids. Samples that can be analysed include biological samples, including serum, urine, fecal fluids or cell-derived materials or food products, in particular dairy products, oils or fats.

Description

Improved method for the analysis of a sample by means of capillary gas chromatography, and means for use in such a method.

The present invention relates to a method for the analysis of a sample by means of gas chromatography, and to means for use in such a method.

In particular, the invention relates to an improved method for the analysis of a sample by means of capillary gas chromatography, which method allows relatively large sample volumes to be (directly) injected and analysed (i.e. qualitatively or quantitatively); and to means for use in such a method. The method and means of the invention are particularly suited for the analysis of samples containing fatty acids, including but not limited to (samples derived from) dairy products and other food products; and also for the analysis of biological fluids such as serum, urine and/or fecal fluid. In general, the method is a powerful technique for trace analysis in capillary gas chromatography. Further uses and advantages of the invention will become clear from the further description given hereinbelow.

Gas chromatography ("GC") is a well-known technique for the qualitative and/or quantitative analysis of a sample, i.e. to determine the presence of and/or the amount(s) of one or substances/components in said sample. In general, in GC, a sample is introduced at or into one end of a column through which a carrier gas is passed. This carrier gas leads the components present in the sample to the other end of the column, where they are detected using a suitable detector. The time it takes for (a) specific component(s) to pass though the column (the so-called "retention time") is determined and can be compared to the retention time for one or more reference compounds and/or to known data, thus allowing identification of the specific component(s) present in the sample. Also, the size of the signal detected for a specific component - e.g. the peak size - may be used as a quantitative measure for the (absolute or relative) amount of said component in the sample.

For a general description of gas chromatography, reference is made to the standard handbooks, for instance "Modern Methods of Chemical Analysis"; R.L. Pecsok and L.D. Shields, Eds.; Wiley Interscience, 1976; pages 85-113. Reference is also made to the articles by Tangerman (1997) and by Tangerman and Nagengast (1996) mentioned hereinbelow. Several different GC techniques are known, which for instance differ in the type of column used and/or in the manner in which the sample is introduced onto said column.

An alternative to the use of packed GC columns involves the use of so-called "capillary columns", e.g. columns with an inner diameter of between 0.10 mm and 0.53 mm and usually with a length of between 5 m and 100 m. When compared to the use of packed GC columns, capillary GC generally offers the advantage of much better resolution capabilities.

However, traditional capillary GC techniques also suffer from a disadvantage in that, because of the small diameter of the capillary columns used, only small amounts of sample can be introduced onto said columns, e.g. of no more than 3 μl, and in particular in the range of 0.1 μl to 3 μl.

Thus, with conventional capillary GC techniques, it is not possible to inject relatively large volumes of samples unless using the so-called "Large Volume Injection" (LVI) technique. This restricts the sensitivity and detection limits that can be achieved with capillary GC columns, in particular when a sample is analysed for components that are only present in trace amounts.

Recently, to circumvent these problems, so-called "Large Volume Injection guard columns" have been developed for use in LVI techniques with capillary columns. However, the use of such guard columns often have a detrimental effect on the analysis/separation, for instance due to the presence of large amounts of non-volatile impurities or due to the presence of large amounts of water in the sample solvent, which both reduce the inertness of the guard column (retention gap), resulting in asymmetric peaks and diminished resolution.

A further disadvantage of conventional capillary GC techniques is that direct injection of biological fluids (serum, urine, fecal supematants) is not possible because of deterioration of the capillary column and because of pollution with heavy sample impurities.

Accordingly, a first general object of the invention is to improve upon the above techniques. According to the invention, this object is generally achieved by the use - in conjunction with a capillary GC column known per se - of a liner (insert, sleeve, pre- column) as further described below, which allows for samples with volumes of up to 250 μl or more to be effectively and efficiently applied onto said capillary column, e.g. by direct injection of the sample (into said liner).

Advantageously it was found that under the circumstances as described in the example there was no detrimental effect of large volumes of evaporated solvent passing onto the column on the end result of the analysis.

In addition, it was found that the use of such a liner offers specific advantages for a number of practical applications, such as the analysis of samples containing fatty acids. Another advantage is the possibility for direct analysis of relatively "dirty" samples. The dirt will be trapped inside the liner by the packing as further described below. Thus, in a first aspect, the invention relates to a method for analysing a sample for one or more components of interest by means of capillary gas chromatography, in which a) said one or more components are carried from a first end of a capillary column to the other end (second end) of said capillary column by means of a carrier gas which is fed through said capillary column from said first end to said second end; b) said one or more components are detected at said second end; which method is characterised in that: the sample is introduced in a liner which contains a particulate packaging material and which is operably connected to said first end of said capillary column, such that when said sample is introduced into said liner, said one or more components pass into said capillary column through said first end.

The invention also relates to an assembly for gas chromatography comprising a capillary column suitable for gas chromatographic purposes provided at one end thereof (first end) with a liner, in which: said liner is operably connected with said first end of said capillary column, such that when a sample containing one or more components to be determined is introduced into said liner, said one or more components may pass into said capillary column through said first end; and said liner comprises a particulate packaging material.

In the above method and assembly, the liner is most preferably essentially as further described hereinbelow.

Preferably, the liner is provided at said first end of the capillary column in such a way that it can easily be replaced after use, i.e. after one or more samples have been analysed using the method and/or assembly of the invention. In this respect, it should be noted that according to the invention, and with advantage, said liner need not be replaced each time a sample has been analysed: instead, it was found that a liner as described herein may be used several times - e.g. for the analysis of up to 100 samples or more - before it has to be replaced. Also, according to an important embodiment of the invention, the liner (i.e. the dimensions thereof, etc.) is specifically adapted for use in - e.g. insertion into - an injection port of a capillary GC apparatus known per se, as further described below.

In another aspect, the invention also relates to a method for providing an assembly as outlined above, said method comprising combining a capillary column suitable for gas chromatography purposes with a liner as described herein, such that said liner becomes operably connected (as indicated above) to a first end of said capillary column, so as to provide an assembly of the invention. The invention also relates to the use of a liner as described herein in such an assembly.

In yet another aspect, the invention relates to an apparatus for capillary gas chromatography, said apparatus at least comprising an assembly as outlined above, and optionally one or more further elements/components of (capillary) gas chromatography apparatus known per se.

The invention also relates to the use of a liner, an assembly and/or an apparatus as described above in analysing a sample, e.g. using the method described above. Other aspects, embodiments and advantages of the invention will become clear from the further description given hereinbelow.

The assembly of the invention is shown schematically in Figure 1 , in which (1) indicates the capillary column and in which (2) indicates the liner.

The liner (2) generally comprises a wall (3) which defines an internal channel (4) with a first end (5) and a second end (6), and a partition (7) which is permeable for the carrier gas and for the one or more components to be determined. Partition (7) essentially divides said internal channel (4) into two essentially separate sections, i.e. a first section (8) which comprises at least one particulate packaging material (9); and a second section (10) in which is provided the first end (11) of the capillary column (1), i.e. in an operable manner as indicated above.

The wall (3) of the liner may be of any suitable material, such as glass, plastic, teflon, metal or another suitable inert material, resisting temperatures up to 300 °C. Also, the wall (3) can have any desired shape, as long as it defines said internal channel (4). Usually, said wall (3) will be a hollow tube with an inner diameter of between 0.5 mm and 2.0 mm, and in particular about 1.0 mm.

The packaging material (9) may be any suitable material which can be used to fill the first section (8) in such a way so as to (still) allow the carrier gas to pass through channel (4)/section (8), and in such a way that the sample to be analysed may be introduced in (between) said packaging material, e.g. by injection using a standard injection syringe for GC purposes. In this invention, the particulate packaging material (9) will comprise beads, granules, spheres, etc. for instance with an average particle size of between 0.5 mm and 2.0 mm. Suitable examples of such materials include, but are not limited to, glass beads, plastic beads, teflon beads and metal beads, or a suitable combination thereof.

According to this invention beads are defined as irregularly ball-shaped particles, granules are defined as regularly or irregularly jagged particles and spheres are defined as substantially round particles. It is to be understood according to this invention that particulate packaging material does not include packaging material consisting of extremely finely divided particles. In this context extremely finely divided particles means particles which are usually identified by a mesh size. Mesh is defined as the number of openings per linear inch, in this context per inch of a sieve or screen. Together with the diameter of the "wire" of which the sieve or screen is made the mesh size determines the diameter of the openings in the sieve or screen and thus is a measure for the particle size. It should be noted that when a particular mesh size is indicated for a particulate material, the majority of the material will have a particle size which is much smaller than the size of the opening that corresponds to the mesh size. In this invention particle size is given in μm or mm. The skilled person is familiar with suitable methods for determining the average particle size of a suitable particulate packaging material, such as for instance light scatering techniques, sieving or even visual inspection using a microscope. The particulate packaging material used in this invention should have an average particle size of more than 100 μm, preferably more than 150 μm, more preferably more than 200 μm, even more preferably more than 250 μm. The particulate packaging material (9) may be essentially inert, or may for instance be such that it can adsorb or bind one or more constituents of the sample to be analysed, in particular the components to be determined, e.g. as further described below for the analysis of samples containing non-derivatized fatty acids. For instance, the particulate packaging material may be a material, e.g. glass, which has an "active" surface and/or which carries on its surface active groups capable of adsorbing undesired components and/or components to be analysed.

The partition (7) may be of any suitable material, as long as it is permeable for the carrier gas and the one or more components to be determined. For instance, the partition may be glass wool, a mesh, a porous membrane, a porous ceramic or another suitable inert material. Also, in order to divide liner (2)/channel (4) into first section (8) and second section (10), the partition (7) may be connected to wall (3), or may be such that it can be removed from liner (2), e.g. in case of glass wool. The partition (7) may be essentially inert or may for instance be such that it can bind one or more of the components to be determined, e.g. as is the case for certain kinds of glass wool as further described below for the analysis of samples containing non-derivatized fatty acids. Packaging material and partition can be made of one and the same material, e.g. glass.

The thickness of the partition (7) is not essential and will usually depend on the material from which said partition (7) is made. Usually, the partition (7) will have a thickness of between 0.5 and 10 mm, for instance about 5 mm for a partition made of glass wool.

Generally, the entire liner (2) may have a length of between 7 cm and 15 cm, depending on the size of the injection port of the GC apparatus. The length of the first section (generally between 7 and 15 cm) and the second section (10) may vary widely, depending on the size of the liner. The first and second section are separated by a partition (7) with a thickness as indicated above.

In a preferred embodiment, (the dimensions of) the liner (2) is such that said liner fits into, and/or is adapted for use in, the injection port of a known GC apparatus, as further described below. For instance, for this purpose, the liner (2) may have a total length of about 8 cm with an external internal diameter of about 6 mm and an internal diameter of about 4 mm, divided by a clot of glass wool of about 5 mm thickness into a first section (8) of about 4.5 cm in length and a second section (10) of about 3.0 cm in length. The first section (8) is filled - i.e. in the manner shown in Figure 1 - with about 2 cm of glass beads with an average diameter of about 1 mm. In second section (10) is provided the first end (11) of the capillary column (1), which first end (11) is positioned at about 0.5 to 2.5 cm from the partition (7). It should be noted that liners comprising glass beads suitable for use as a packaging material in the present invention have already been described per se in the art, vide A. Tangerman, Clinical Chemistry 43:6, 1003-1009 (1997), as well as A. Tangerman and F.M. Nagengast, Analytical Biochemistry 236, 1-8 (1996). However, in these references, these liners are used in conjunction with a packed GC column, and not with a capillary GC column. In this respect, it should inter alia be noted that when using packed GC columns, there is generally no upper limit as to the size of the sample that may be introduced onto said columns. Thus, the above references teach the skilled person nothing on solving the problem(s) underlying the present invention, i.e. to allow for analysis of samples of large volume when using capillary GC columns, and in particular when using direct injection techniques.

When the assembly of the invention is used, a carrier gas is led through/fed into internal channel (4) essentially from first end (5), i.e. in the direction of the arrow shown in Figure 1. Said carrier gas then passes through first section (8)/particulate packaging material (9) and thereafter through partition (7) into section (10), from where the carrier gas enters capillary column (1) through first end (11). For this purpose, the first end (5) of the liner (2) is connected to a source of the carrier gas. The second end (6) of the liner (2) may be essentially sealed, with the capillary column (1) protruding through said seal into second section (10). However, the second end (6) may also be left open, without any further seal or precaution(s), as long as the capillary column (1) and the liner (2) are still operably connected.

When a sample is (to be) analysed using the assembly of the invention, said sample is preferably introduced into section (8), and in particular into particulate packaging material (9). For instance, when the packaging material consists of glass beads, (a pre- determined volume of) the sample may be injected in between said glass beads using standard GC injection equipment, such as a Hamilton injection syringe. Injection in between the glass beads ensures immediate contact of the injected sample with hot glass, thereby facilitating immediate volatilization, resulting in better-resolved and sharper peaks of the various components in the sample. Moreover, injection in between glass beads largely increases the glass surface area in the injection area, thereby resulting, in case of dirty samples, in an evenly distributed contamination of the glass beads in the injection area. The latter results in a prolonged lifetime of the liner. (2). Upon injection of the sample into the particulate packaging material (9), one or more of the components to be determined are carried by the carrier gas through partition (7) into section (10), from where they enter the capillary column (1) through first end (11), i.e. with the flow of the carrier gas. The one or more components are then carried through column (1) to the second end thereof (not shown), where they exit said column (1) and can be detected, e.g. by means of a detector (not shown), in a manner known per se for capillary GC. It should be noted that in a preferred embodiment the sample that is introduced into the liner is passed splitless into the capillary column.

Optionally, when the particulate packaging material (9) or the partition (7) has an "active" surface capable of binding/adsorbing one or more of the components to be determined, said components may first be desorbed from the particulate packaging material or partition, e.g. by injection into first section (8) of liner (2) of a suitable solvent and/or desorbant, such as formic acid for desorbing fatty acids.

Also, in the method of the invention, the one or more of the components to be analysed may first be concentrated at or near the first end of the capillary column, e.g. by keeping the temperature of the column relatively low when said components first enter the capillary column (e.g. upon release/desorption from the packaging material), whereupon the separation of said one or more components may be achieved by increasing the column temperature. Generally, the liner and method(s) described above may be used in combination with any known capillary column, carrier gas and/or detection technique known per se. For this purpose, the assembly of the invention may be (operably) combined with one or more components of GC equipment known per se, such as a source of the carrier gas, a heating element for the capillary column or a detector, i.e. to provide an entire capillary GC apparatus, which constitutes a further aspect of the invention.

Preferably, however, the liner of the invention is used in conjunction with a known apparatus of capillary GC, i.e. by providing the capillary column present in said apparatus with a liner in the manner disclosed herein. In a particularly advantageous embodiment, the liner of the invention is used/inserted in(to) an injection port of a known capillary GC apparatus, such as a Chrompack Model CP 9001 capillary gas chromatograph so as to form an assembly of the invention with the capillary column. This may be for instance carried out essentially as described in the references by Tangerman (vide for example Figure 1 thereof) and by Tangerman and F.M. Nagengast (vide again Figure 1 thereof) for packed GC columns; in which according to the present invention (the first end of) the capillary column (1) is operably connected to said liner (2), e.g. essentially as shown in Figure 1 of this application.

Also, as mentioned above, the liner is preferably provided in such a manner that it can easily be replaced, again essentially as outlined by Tangerman and by Tangerman and Nagengast for the use of liners with packed GC columns.

The liner, assembly and method outlined herein may be used for the analysis, detection and/or (quantitative or qualitative) determination of any sample and/or component(s) that may be determined using conventional GC techniques, and in particular conventional capillary GC techniques. For these purposes, as mentioned above, the invention allows for large sample volumes - e.g. up to 250 μl or even more, and in particular larger than 1 μl - to be analysed directly - i.e. by injection into the liner - without the need for any pre-treatment of the samples such as pre-concentration. Depending on solvent, analyte and column conditions sample volumes of up to 1 ml or even more may be applied. The skilled person will be able to ascertain if the circumstances allow such large volume injections. Thus, the use of a liner of the invention allows/provides both direct injection as well as Large Volume injection. However, it should be noted that the method of the invention is not limited to samples of such large volume, but that generally, the method of the invention may be used to analyse samples of any volume, e.g. generally between 0.1 μl and 250 μl.

The analysis may further be carried out in a suitable manner known per se, using well known columns, carrier gases, gas flows, column temperatures and (further) conditions known per se, as will be clear to the skilled person, and depending upon the sample to be analysed and the components (suspected to be) present therein. For instance, suitable conditions for the analysis of fatty acids present in a sample

(e.g. further outlined below) may for instance comprise: a fused silica capillary column, loaded with FFAP (15 m x 0.53 mm i.d., J&W Scientific, Folsom, USA; particulate packaging material: glass beads (optionally teflon or metal beads); - size of the liner: as indicated above; carrier gas: helium, flow 20 ml/min; column temperature: between 65 °C and 240 °C; injector temperature: 200°C detector temperature: 180°C detection technique: flame ionization detection.

Also, when glass beads are used as the particulate packaging material and glass wool as the partition for the analysis of fatty acids, the method of the invention further comprises a desoφtion step essentially as described above and below in the Example (e.g. using formic acid); and/or a step of concentrating the fatty acids at the first end of the capillary column, also essentially as described above and in the Example.

Usually, the component(s) to be analysed will be one or more volatile components, with any non-volatile components and/or other impurities or undesired components present in the sample remaining and/or being retained in first section (8), e.g. by partition (7) or particulate packaging material (9). With advantage, this prevents these non-volatile components and/or impurities to enter into and/or clog the capillary column (1). For instance, using the liner of the invention, urine samples and/or samples of fecal fluid may be injected and analysed directly by injection into the liner. In addition, the use of the liners of the invention may also offer one or more of the following advantages, alone or in any combination: improved detection limits, in particular for components which are only present in trace amounts in the sample to be analysed. improved results of the separation/detection, and in particular improved quantitative results; improved reproducibility; the liners can be produced at relatively low cost, and can easily be replaced. Furthermore, it has been found that the use of the liners described above offers particular advantages in or for some specific applications, including but not limited to: - analysis of biological fluids and/or materials such as blood, serum, urine or fecal water, e.g. for components such as ethanol and fatty acids; analysis of fatty acids, e.g. in food products, in particular dairy products, oils and fats

In particular, it was found that the liner can be used with advantage for the analysis, detection and/or (qualitative and quantitative) determination of (samples containing) fatty acids, including but not limited to - saturated or unsaturated - short chain fatty acids (C2- C6), medium chain fatty acids (C8-C12) and long chain fatty acids (C14-C22), or (samples containing) mixtures thereof. In the art, for the determination of such fatty acids using a capillary column, it was so far almost in all instances necessary to first derivatize these medium and long chain fatty acids - e.g.. by quantitative conversion into the corresponding methyl- or ethyl esters - prior to analysis. When the liner and method of the invention is used, such pre-treatment is not longer required, not even in the case of large volume sample injections, provided that an appropriate capillary column is used, thus resulting in a faster and more reliable technique.

Upon injection of the sample into the particulate packaging material, the fatty acids are bound to (active residues present on) the surface of the particulate packaging material (9) or bound to active sites on partition (7) (glass wool) and thus remain inside the liner, whereas any solvent used - e.g. heptane or another suitable (preferably organic) solvent or solvent mixture - is evaporated and is led through the capillary column. This makes it possible to (directly) inject large volumes of sample. Thereafter ( e.g. after a few minutes) the fatty acids are desorbed from the packaging material (9) or from partition (7), e.g. by injection of formic acid into the particulate packaging material, upon which said fatty acids enter the capillary column. When using an inert packaging material (e.g. teflon beads) and partition, the fatty acids are no longer bound inside the liner. In that case the fatty acids can be concentrated at the beginning of the capillary column, provided that the temperature of the capillary column is initially kept relatively low.

In this way, the invention provides for an excellent separation of fatty acids, for instance those fatty acids which are important for the food industry, such as mono- and polyunsaturated fatty acids (e.g. in or from fish oils, vegetable oils, margarine and similar products).

The invention will now be demonstrated by means of the following non-limiting Example.

Example: Analysis of underivatized fatty acids.

The liner and the method of the invention were used for the analysis of underivatized fatty acids. The capillary column used was a fused silica capillary column, loaded with FFAP (15 m x 0.53 mm id., J & W Scientific, Folsom, USA). The liner was a tube of 8 cm length and 4 mm inner diameter (outer diameter 6 mm), filled with 2 cm glass beads of 1 mm diameter, held in place by a plug of glass wool of 0.5 mm thickness (essentially as shown in Figure 1). This liner fits in the injection port of a Chrompack Model CP 9001 gas chromatograph. Instead of using glass beads and glass wool, more inert materials such as teflon may be applied.

When the liner of the invention was used, it proved possible to inject samples of more than 200 μl directly without significantly influencing the analysis. Also, as no pre- treatment/pre-concentration of the sample is required prior to injection/analysis, the method of the invention also allows for the detection/determination of relatively volatile fatty acids, such as C₂-Cι₂ fatty acids, which are usually evaporated when a pre- concentration is applied to the sample.

Before injection, the sample containing free fatty acids and/or esterified fatty acids, e.g. to glycerol, is first subjected to hydrolysis with ethanolic potassium hydroxide, resulting in free fatty acids. After acidification, the free fatty acids are taken up in a suitable solvent (heptane).

Upon injection of a sample of such fatty acids in a suitable solvent (heptane) into a particulate packaging material of glass beads (i.e. essentially as outlined above), said fatty acids are bound to active groups on the surface of the glass beads or to the glass wool and thus remain inside the liner. The solvent evaporates and passes through the column. This makes it possible to inject large volumes of sample.

After about 2 minutes, the particulate packaging material is injected with excess formic acid, which essentially quantitatively (e.g. > 98% of the amount injected into the particulate packaging material) desorbs the fatty acids from the packaging material (glass beads) or from the partition (glass wool), which thereupon enter the capillary column for

(further) separation, detection and analysis.

When during such separation/analysis, the temperature of the capillary column is initially - e.g. for at least 1 minute after injection of the formic acid - kept relatively low - e.g. at about 65 °C - this achieves a further concentration (step), as the fatty acids remain

(concentrated) at the beginning of the capillary column. Thereafter, the temperature of the column is raised to 240 °C (at a rate of 10 °C/min), for the separation/analysis of the fatty acids. Helium was used as a carrier gas and the fatty acids were detected using a flame ionization detector. When using a liner with an inert particulate packaging material and an inert partition, e.g. an all teflon liner, including teflon beads, no binding of fatty acids takes place inside the liner, upon injection of a sample containing fatty acids. Concentration of fatty acids then only takes place at the beginning of the capillary column, provided the initial column temperature is kept low. In this case no desoφtion of fatty acids with excess formic acid is necessary and injection of fatty acids in e.g. heptane is sufficient, facilitating the use of automatic sample injection.

Using this method, it was possible to achieve, in a single run, excellent separation of all major underivatized fatty acids, e.g. from C2 (acetic acid) to C22:6 (docosahexaenoic acid, DHA, from fish oil) in very low concentrations.

For instance, this method may be applied to the (qualitative and/or quantitative) determination of fatty acids in biological samples such as serum and samples derived from cells; oils and fats; margarine, butter and other dairy products; and food preparations and/or supplements such as lecithin.

Claims

C L A I M S

1. Method for analysing a sample for one or more components of interest by means of capillary gas chromatography, in which a) said one or more components are carried from a first end of a capillary column to the other end (second end) of said capillary column by means of a carrier gas which is fed through said capillary column from said first end to said second end; b) said one or more components are detected at said second end; which method is characterised in that: - the sample is introduced in a liner which contains a particulate packaging material and which is operably connected to said first end of said capillary column, such that when said sample is introduced into said liner, said one or more components pass into said capillary column through said first end.

2. Method according to claim 1, in which the liner (2) comprises a wall (3) which defines an internal channel (4) with a first end (5) and a second end (6), and a partition (7) which is permeable for the carrier gas and for the one or more components to be determined and which essentially divides said internal channel (4) into a first section (8) comprising the particulate packaging material (9), and a second section (10) in which is provided the first end (11) of the capillary column (1).

3 Method according to claim 1 or 2, in which the particulate packaging material comprises beads, granules or spheres.

4. Method according to any of the preceding claims, in which the particulate packaging material has an average particle size of more than 100 μm, preferably between 0.5 and 2.0 mm.

5. Method according to any of the preceding claims, in which the sample has a volume of more than 0.1 μl, in particular more than 1 μl, optionally more than 250 μl.

6. Method according to any of the preceding claims, in which, upon injection of the sample into the liner, one or more of the components of interest are adsorbed onto the particulate packaging material and/or partition, and are subsequently desorbed in a separate step, preferably by introducing a solvent for said components into the particulate packaging material and/or partition.

7. Method according to any of the preceding claims, in which one or more of the components of interest are first concentrated at the first end of the capillary column, preferably by keeping the temperature of the column relatively low, followed by separation of said one or more components on the column, preferably by increasing the column temperature.

8. Method according to any of the preceding claims, wherein the components of interest are free or esterified fatty acids, preferably underivatized fatty acids.

9. Method according to any of the preceding claims, wherein the sample is a biological sample, including serum, urine, fecal fluid or cell-derived materials or a food product, in particular a dairy product, oil or fat.

10. Assembly for gas chromatography comprising a capillary column suitable for gas chromatographic puφoses provided at one end thereof (first end) with a liner, in which: said liner is operably connected with said first end of said capillary column, such that when a sample containing one or more components to be determined is introduced into said liner, said one or more components may pass into said capillary column through said first end; and - said liner comprises a particulate packaging material.

11. Assembly according to claim 10, in which the liner (2) comprises a wall (3) which defines an internal channel (4) with a first end (5) and a second end (6), and a partition (7) which is permeable for the carrier gas and for the one or more components to be determined and which essentially divides said internal channel (4) into a first section (8) comprising the particulate packaging material (9), and a second section (10) in which is provided the first end (11) of the capillary column (1).

12. Assembly according to claim 10 or 11, in which the particulate packaging material comprises beads, granules or spheres.

13. Assembly according to any of claims 10-12, in which the particulate packaging material has an average particle size of more than 100 μm, preferably between 0.5 and 2.0 mm.

14. Assembly according to any of claims 10-13, in which the particulate packaging material is made of glass, plastic, teflon or metal.

15. Assembly according to any of claims 10-14, in which the capillary column is part of a capillary GC apparatus, and in which the liner has dimensions adapted for use in the injection port of said capillary GC apparatus.

16. Apparatus for capillary gas chromatography, at least comprising an assembly according to one of claims 10-15, and optionally one or more further components of a (capillary) gas chromatography apparatus known per se.

17. Use of an assembly according to any of claims 10-15, and/or an apparatus of claim 16, in analysing a sample.