DE3930654A1 - MULTIDIMENSIONAL CHROMATOGRAPHIC ARRANGEMENT - Google Patents

Abstract

An on-line multidimensional system (10) includes a liquid chromatograph (12) having an on-line connection (22) to a pyrolysis probe (24), which in turn has on-line connection (54) to a gas chromatograph (48). Preferred applications use a size-exclusion chromatographic coupled to a pyrolysis probe coupled to a gas chromatograph to simultaneously produce composition as a function of molecular weight/size information for polymeric materials. <IMAGE>

Description

The present invention relates generally on multidimensional chromatography and in particular on a directly (on-line) connected LC / GC arrangement, that is able to provide information about composition to supply with volatile components.

Multidimensional chromatography can be an effective instrument for separation, especially if it is a complex matrix that requires an unreachable high number of theoretical plates for a sufficient resolution. Furthermore, multidimensional chromatography has proven to be very suitable when it comes to samples that require careful cleaning steps before analysis. The connection of a liquid chromatograph (LC) and a gas chromatograph (GC) in an "on-line" mode of operation is described in the following references: "On-line Multidimensional Chromatography Using Packed Capillary Liquid Chromatography And Capillary Gas Chromatography," by HJ Cortes et al., In HRC & CC, 8 (1985) 469; "Determination Of Trace Chlorinated Benzenes in Fuel Oil by On-Line Multidimensional Chromatography Using Packed Capillary Liquid Chromatography and Capillary Gas Chromatography," by HJ Cortes et al., In Journal of Chromatography, 349 (1985) 55 and "On-Line Multidi mensional Chromatography Using Micro HPLC-Capillary GC. " by HJ Cortes et al, in Chromatography Forum, 4 (1986) 29.

As can be seen from this work, columns for high-resolution liquid chromatography (HPLC) in an on-line operation are mainly used for the detection of trace components in a complex matrix, the LC providing a highly effective purification step, and a section of the Chromatogram containing the components of interest is transferred to a GC for further resolution and quantification. A similar arrangement is also used to separate components by type, as described in "Coupling Micro LC-Capillary GC as a Powerful Tool for the Analysis of Complex Mixtures," by Duquet et al., In HRC & CC, 11 (1988 ) 252.

However, there is a fundamental limitation for the use of this LC / GC technology in the type of connections that can be analyzed by the GC . In other words, the compounds must be volatile and chromatographable in the gas phase. Difficult or highly polar compounds can be analyzed by GC if they are chemically treated (derivatized) to convert them into a more suitable form (see Handbook of Derivatives For Chromatography, by K. Blau et al., Heyden & Son, Ltd., London (1978). However, the need to chemically treat these compounds presents great difficulties in on-line or continuous multidimetric analysis of such low volatility or highly polar compounds.

An alternative is the use of pyrolysis gas chromatography to investigate volatile pyrolysis fragments of a non-volatile molecule. When characterizing polymers, a combination of size exclusion chromatography (SEC) and pyrolysis gas chromatography allows the average polymer composition to be determined as a function of molecular size / weight. However, this information is difficult to access because fractions eluted from an SEC assembly are typically manually collected, evaporated, redissolved in a suitable solvent, and manually syringed into a pyrolysis assembly.

Accordingly, it is the main aim of the present invention dung, an arrangement for connecting liquid and to develop gas chromatography which is an on-line multidimensional analysis or the determinations of low volatility or highly polar connections allowed. The expression used in this regard "Low volatility" refers to connections with non-volatile and / or highly polar properties.

Another object of the present invention is to combine size exclusion chromatography (SEC) and pyrolysis gas chromatography in an on-line arrangement to enable determination of the average polymer composition as a function of molecular size / weight. as well as to provide valuable information for understanding polymer properties and polymer chemistry.

Another object of the present invention is to provide a multidimensional on-line arrangement that is capable of automatically collecting fractions of interest from an SEC and transferring them to an interface to enable GC analysis .

To achieve the foregoing objectives, the present invention provides a multidimensional on-line arrangement that includes a micro size exclusion chromatograph and a switchable shutoff device for withdrawing the fractions eluted from the SEC . The switchable shut-off device transfers these removed fractions directly into a pyrolysis arrangement in which volatile fragments are generated which are characteristic of the non-volatile constituents from the removed fractions. The arrangement also includes a gas chromatograph to provide molecular size / weight distribution of the volatile fragments. The present invention also enables the combination of shut-off device, pyrolysis arrangement and gas chromatograph for use as an auto-injector when the SEC or other LC is not connected to the arrangement.

The switchable shut-off device contains separate ones Sample and solvent rinse loops and causes a carrier fluid the contents of these loops successively transported to the pyrolysis arrangement. The Pyrolysis arrangement contains a pyrolysis tape that is coaxial is arranged in a glass housing. The housing of the Pyrolysis arrangement contains a recessed side Area, which the examined fractions on a conducts narrow section of the pyrolysis tape. The housing the pyrolysis arrangement also allows the supply of additional carrier liquid to keep the evaporation Increase the speed of the solvent and the Opportunity for the solvent to flow along the Distribute pryrolysis tapes, keep them as low as possible.

In particular, the present invention relates to a chromatographic device for multidimensional on-line analysis of a sample that is a volatile Contains ingredient comprising a liquid chro matographs for the separation of a sample with a non-volatile component in a fraction of inte which contains the non-volatile component, a pyrolysis arrangement, means to make a fraction of Interest from the liquid chromatograph too elute and transfer to the pyrolysis arrangement and  a gas chromatograph, which is used to extract the gas from the Pyrolysis arrangement to absorb and discharge gas to separate its components.

The invention further relates to a method for multidimensional online analysis of samples contain non-volatile components, including the Steps to separate the samples into fractions of Interest in the direct (on-line) transfer of the Fractions in a pyrolysis arrangement, for pyrolysis of these fractions to create volatile fragments for direct (on-line) transfer of volatile questions elements in a gas chromatograph and to the chromatogra phical separation of the volatile fragments and detection of the separated fractions.

The invention further relates to an auto-injector direction, comprising a transfer arrangement for opening take a sample with a volatile Component, a pyrolysis arrangement in connection with the transfer arrangement for the generation of volatile Fragments characteristic of the volatile Part of said sample and a gas chro matographs for recording at least part of the volatile fragments from the pyrolysis arrangement and Analysis of volatile fragments.

The invention further relates to a chromatographic On-line multidimensional analysis device of compositions with low volatility len, comprising a size exclusion chromatograph, a shut-off device for taking fractions that from which size exclusion chromatographs were eluted a pyrolysis arrangement connected to the shut-off direction for the generation of volatile fragments, the characteristic of the non-volatile components  from the examined fractions and a gas Chromatograph for recording at least one part the fragments from the pyrolysis arrangement for analysis of the volatile fragments.

Other advantages and properties of the present Invention will become apparent from the detailed description of the preferred embodiments explained the following figures.

Fig. 1 is a graphical representation of a multi-dimensional on-line assembly according to the present invention.

Figs. 2A and 2B are graphical representations of the loading and injection positions of the switchable shut-off device with a plurality of openings in FIG. 1.

Fig. 3 is a graph showing a micro-SEC chromatogram of a styrene-acrylonitrile copolymer.

FIG. 4 is a graph showing a capillary GC chromatogram of pyrolysis products of a fraction of the styrene-acrylonitrile copolymer of FIG. 3.

Fig. 5A to 5D are graphs capillary GC-Cro matogramme a polystyrene Homopo lymers show at different separation conditions.

FIGS. 6A-6B are graphs capillary GC-Chro matogramme a styrene homopolymer at two different temperatures Interfacial show.

Fig. 1 shows a multidimensional on-line chromatography arrangement 10 according to the present invention. The arrangement 10 includes a liquid chromatograph 12 , which has a solvent pump 14 , an injection valve 16 , one or more columns 18 and a detector 20 . In one embodiment of the present invention, the solvent pump is an Isco Micro-LC 500 solvent delivery system (Isco, Lincoln, Nebraska, USA) which is operated at a constant flow rate. Accordingly, injector 16 is a Valco Model NI4W injector (Valco Instruments, Houston, Texas, USA), with an injection volume of 200 nanoliters (nl). In addition, the detector is a Jasco Uvidec V detector (Jasco International, Japan), which is equipped with a modified cell, the illuminated volume of which was calculated from the capillary diameter and the gap size with 6 nl. Such modified cells are described in "Fused Silica, Narrow Bore Microparticle Packed Column HPLC", by FJ Yang in Journal of Chromatography, 236 (1982), 265.

The columns 18 are made of fused silicate capillaries with an inner diameter of 250 micrometers (µm) from Polymicro Technologies, Phoenix, Arizona, USA, and have a column length of 50 cm. A porous ceramic carrier bed was used as described in "Porous Ceramic Bed Supports for Fused Silica Capillary Columns Used In Liquid Chromatography" by HJ Cortes et al., In HRC & CC, 10 (1987) 446. The columns 18 were packed with Zorbax PSM-1000 with 7 µm particle diameter as a slurry in acetonitrile at a pressure of 6000 psig (41 470 kPa).

The liquid chromatograph 12 is preferably a micro-SEC system (e.g. for the characterization of polymers). However, the broad scope of the invention is in no way intended to be limited to a microsystem or size-exclusion chromatography, since the choice of column dimension and type is determined by the sample and the desired information. In this regard, a micro SEC system was chosen for the LC 12 because the components of interest are diluted in much less volume than in a common SEC column. This property allows the research of a polymer in relatively few steps. However, if a more precise analysis is desired, smaller steps or fractions can also be analyzed. Small-caliber or conventional columns can be used. Therefore, the analysis can provide a larger number of determinations over a smaller molecular size range. Because an SEC separates molecules by size and the size of a molecule is related to its molecular weight, the term "molecular size / weight" used here generally refers to molecular size and / or molecular weight.

The arrangement 10 also contains a switchable shut-off device 22 with a plurality of openings for transferring the eluted fractions of interest from the micro-SEC 12 into a pyrolysis arrangement 24 . In one embodiment of the present invention, the shut-off device 22 is a Valco 10-opening shut-off device, model NI10WT. As can be seen from FIGS. 2A and 2B, this shut-off device was equipped with a 1.0 microliter (μl) sample loop 26 and a 5.0 μl solvent rinsing loop 28 . Both of these loops 26 and 28 were made from 50 µm solvent ID ID silica tubing. A short length of this tubing was also used for line 30 between shut-off device 22 and pyrolysis assembly 24 , as well as for line 32 between shut-off device 22 and detector 20 of Micro-SEC 12 .

Fig. 2A shows the shut-off device 22 in a "load" position, which causes separation of the sample and Spülschleife. In contrast, FIG. 2B shows the shut-off device 22 in an "injection" position, in which the sample and the rinsing loops are connected. In the loading position, the outflowing medium flows out of the SEC detector 20 through the sample loop 26 via the line 32 . The outflow from the sample loop 26 can either be stored or transferred to a waste container. Therefore, when the shut-off device 22 is in the loading position, a suitable solvent (e.g. THF) can flow through the rinsing loop 28 .

When the shut-off device 22 is switched to the injection position, the sample loop 26 is connected to the rinsing loop 28 , so that the content of these loops is transported into the pyrolysis arrangement 24 with a suitable carrier liquid (e.g. helium). In addition, another gas, such as air, can be introduced to clean the system. Although other suitable arrangements of the switchable shut-off device can also be used, the use of a rinsing loop is preferred because this enables the connecting lines from the micro-SEC 12 to the pyrolysis arrangement 24 to be cleaned before the next sample is collected.

While in the preferred arrangement of the shut-off device, a predetermined amount of the outflow from the SEC 12 is collected in a sample loop, other suitable arrangements of the shut-off device can be used for a suitable application. For example, a construction of the shut-off device could be used in which one can choose between an injection and a bypass position, so that the outflow flows into the pyrolysis arrangement, unless it is discharged into a waste container. Once the outflow is derived, then a carrier liquid can be used to convey the part of the outflow that has already flowed through the shut-off device into the pyrolysis arrangement 24 .

The pyrolysis assembly 24 generally includes a pyrolysis tape 34 that is coaxially disposed in a glass chamber of the housing 36 . In one embodiment of the present invention, the pyrolysis plant used is a Hewlett Packard Model 18 580 A pyroprobe (Hewlett Packard Instruments, Avondale, Pennsylvania, USA), which was operated at a temperature of 700 ° C. in one-second intervals. The housing 36 contains a cylindrical part, through which the pyrolysis tape 34 extends, and a laterally arranged cylindrical part 40 , which projects approximately at right angles from the cylindrical part 38 . The housing 36 is also wrapped with a heating tape 41 which is heated to a temperature of about 180 ° C (external surface temperature) at the appropriate time.

In one embodiment of the present invention, a lowered or recessed section 43 is located in the pyrolysis belt 34 directly below the side part 40 of the housing 36 . The recessed section 43 in the pyro lysis bands 34 serves to receive individual separated fractions of interest from the shut-off device 22 via the line 30 . In this regard, the recess 43 serves to restrict this liquid flow to a certain section of the pyrolysis belt 34 . Thus, the recess 43 causes the weiterbe promoted fraction is applied to a limited, reproducible portion of the pyrolysis tape 34 .

The inlet opening 42 of the side part 40 also allows an additional carrier gas (e.g. helium, nitrogen or air) to be introduced into the housing 36 via the line 44 . The flow rate of this additional carrier gas is adjustable in order to control the evaporation rate of the solvent introduced into the pyrolysis arrangement 24 . In this way, the evaporation rate can be increased, thereby minimizing the opportunity for the solvent and sample to spread over the pyrolysis belt 34 .

The housing 36 of the pyrolysis assembly 24 also contains an exit opening that allows the volatile fragments generated by the pyrolysis belt 34 to be transferred to a gas chromatography device 48 . A short capillary tube 50 extends from the outlet opening 46 . The screw connections 52 serve to connect the capillary tube to the three-way T-piece 54 with a small dead volume to separate the outflow from the pyrolysis arrangement 24 . A portion of this effluent is passed to columns 56 of gas chromatography device 48 while the remainder is vented through line 58 . A microdosing valve 60 is connected to line 58 to control the separation ratio of deaerated liquid to liquid transferred to the GC. On the other hand, a switching valve, such as a Walco model N4WT, can also be fitted between the housing outlet 50 and the T-piece 54 in order to allow the solvent to be vented quickly.

In one embodiment of the invention, the gas chromatography arrangement used is a Varian Model 3700 gas chromatograph (Varian Associates, Walnut Creek, California, USA) with a flame ionization detector 62 . Correspondingly, the analytical columns 56 consisted of 50 m × 0.20 mm ID phenylmethyl silicone of 0.33 μm film thickness (Hewlett Packard, Avondale, Pennsylvania, USA). The temperature program used started with 6 minutes at 50 ° C, then the temperature was increased at intervals of 10 ° C or 20 ° C per minute to 220 ° C. The temperature program was started at the time of pyrolysis and preferably ran after the solvent was removed from the system. The carrier gas used was helium and the fresh gas fed into detector 62 was nitrogen (at 20 ml per minute).

Before carrying out the experiments, SEC columns 18 were calibrated using narrow distribution anionic polystyrene standards (Polymer Labs, England). The column performance was estimated by measuring the asymmetry factor as described in "Introduction to Modern Liquid Chromatography" by J. Kirkland et al., J. Wiley & Sons, New York (1979). With toluene as a fully permeated molecule, the asymmetry factor was determined at 1.04 and the column efficiency at 38,000 trays per meter. The resolution was estimated according to the following equation:

R = D σ = [d log M / dv ( Δ V) ] = log M ,

where D is the slope of the calibration curve, σ is the standard deviation of toluene, V is the elutation volume and M is the molecular weight. In the described embodiment, the resolution factor was 0.034.

It is known that the elution volume in an SEC increases with the sample concentration due to the change in the hydrodynamic volume of a polymer in solution with the concentration. In addition, a high sample concentration can cause band broadening due to the viscous flow of the solid band. Therefore, for the particular polymer and experimental conditions, it is preferred that the amount of polymer injected into SEC columns 18 be no more than 2 micrograms (µg) to obtain accurate molecular weight distributions based on those above described calibration pro cedure.

The preferred solvent for the mobile phase, the was used for this specific application HPLC-pure tetrahydrofuran (Fisher Scientific, Fairlawn, New Jersey, USA). In this regard, fraud the flow rate of the solvent 2.01 µ per minute what results in a column head pressure of 1300 psig (9067 kPa) would have. It is known that one through the apparatus fluctuation of the flow rate large errors in the Calculate the molecular weight of the sample can. Around these expected fluctuations in the flow rate to balance, it is therefore preferred that a small Amount of toluene added to the injected polymer solution to deliver an internal standard.

The use of the on-line SEC / pyrolysis GC arrangement 10 for the characterization of a styrene-acrylonitrile copolymer is shown in FIGS . 3 and 4. Figure 3 shows the micro-SEC chromatogram of the polymer prepared by dissolving 10 mg / ml in THF. The various fractions that have been transferred to the pyrolysis interface 24 are indicated in the chromatogram. FIG. 4 shows the capillary GC chromatogram after pyrolysis of fraction No. 1 from FIG. 3, whose molecular weight was between 1,800,000 and 450,000. This GC chromatogram is typical of GC chromatograms that are obtained after pyrolysis of the appropriate range of molecular weight distribution.

The relative composition of each fraction of the eluted copolymer was measured by measuring the area ratio of the acrylonitrile and styrene peaks found. This information is important when determining the relative composition as a function of the molecular size. In this regard, it was found that the position of the pyrolysis arrangement causes a variability in the measured values of the area ratios. During the pyrolysis process, the platinum band 34 bends and rarely returns exactly to its original position. Because of this change in position, it is therefore difficult to deposit the fractions of interest in the same place on the band as previous fractions. Since the belt 34 does not heat uniformly over its length, it is possible that the transferred fractions are exposed to different pyrolysis temperatures and therefore produce different results. However, as described above, the establishment of the recess 43 in the pyrolysis belt 34 limits the transferred fractions to a reproducible section and enables a removable standard deviation of the area ratios (for example 2.4%) to be achieved.

Ideally, the entire pyrolyzed fraction should be transferred to GC columns 56 . However, it was found that the pyrolysis assembly 24 had to be purged at a high carrier gas flow rate in order to obtain relatively sharp peaks. This situation was further exacerbated because the GC columns 56 generated relatively high pressures and therefore resisted the use of high flow rates from the pyrolysis assembly 24 . In this connection it should be noted that the installation of the T-piece 54 was helpful in order to achieve a sufficiently high flow rate. On the other hand, the use of large-diameter capillaries can also allow a quick transfer of the fragments into the columns 56 , without resorting to a separation arrangement. On the other hand, the function of the separator can also be fulfilled if it is replaced by a cryogenic focusing arrangement or a trap, such as a solid absorbent.

In Figs. 5A-5D is a series of GC-Chro shown matogrammen to the experimental effects of various separation conditions at the T-piece 54 to illustrate in control of the valve 60. To carry out these experiments, the sample was prepared by dissolving 70 mg of a polystyrene homopolymer GC and the arrangement was heated in order to keep a condensation of the fragments of interest as low as possible and thereby avoid poor chromatography. With regard to the multidimensional arrangement 10 according to the present invention, FIGS . 6A and 6B show the effect of two different pyrolysis interface temperatures. Both GC chromatograms were obtained by chromatographing the pyrolysis products of a styrene homopolymer, which was prepared according to the method described above to determine the effect of various separation ratios and was applied to the pyrolysis tape 34 .

Fig. 6A shows the chromatogram at an interface temperature of 25 ° C, while Fig. 6B shows the result at an interface temperature of 180 ° C. As can be seen from these figures, the shape of the peak improves considerably at the higher interface temperature. However, it was found that when the interface 24 was heated during the transfer, the sample splashed more easily so that part of the polymer was deposited on the walls of the interface instead of on the pyrolysis tape 34 . This resulted in reduced sensitivity and made the reproducibility of the results unpredictable. Accordingly, it is preferred that the transfer of the fractions of interest, depending on the solvent used, be carried out at a temperature at which there is no excessive boiling. After completion of the transfer, the assembly 24 can then be heated to a suitable temperature, such as 180 ° C.

For a specialist with knowledge of the previous Revelation makes it possible to make modifications here perform specific embodiments described ren without losing the basic idea of the present Er change. Such modifications are in the Scope of the present invention.

Claims (12)

1. A chromatographic device for multidirectional on-line analysis of a sample containing a non-volatile component, comprising:
a liquid chromatograph ( 12 ) for separating a sample with a non-volatile component into a fraction of interest containing the non-volatile component;
a pyrolysis arrangement ( 24 );
Means for transferring a fraction of interest eluted from the liquid chromatograph to the pyrolysis assembly; and
a gas chromatograph ( 48 ) arranged to receive the gas stream from the pyrolysis arrangement and to separate it into its components. 2. Arrangement according to claim 1, wherein said transfer means consists of a shut-off device ( 22 ) in order to selectively receive a defined volume of the fractions eluted from the liquid chromatograph ( 12 ) and these fractions in the pyrolysis arrangement ( 24 ) convict. 3. Arrangement according to claim 1, wherein the Absperrvor direction ( 22 ) consists of a switchable Absperrvor direction with many openings, which has a loading position (A) and an injection position (B) and the loading position causes a separation of sample and rinse loops and the A spraying position connects the sample and rinse loops and causes a carrier liquid to convey the contents of the sample and rinse loops one after the other into the pyrolysis arrangement ( 24 ). 4. Arrangement according to claim 2, wherein the Absperrvor direction ( 22 ) is a switchable shut-off device with an injection and a bypass position, which allows a direct transfer of the outflow from the liquid chromatograph into the pyrolysis arrangement ( 24 ). 5. Arrangement according to one of the preceding claims, wherein the pyrolysis arrangement ( 24 ) contains a pyrolysis tape ( 34 ) with a recess ( 43 ) in order to limit the transferred portion to a reproducible section and the tape is in a housing ( 36 ) has an inlet ( 42 ) for receiving said removed fractions from the liquid chromatograph and an outlet ( 46 ) for transferring the fragments produced into the gas chromatograph ( 48 ), and wherein the inlet ( 42 ) also contains an opening for receiving contains an additional carrier liquid. 6. Arrangement according to one of the preceding claims, wherein the gas chromatograph contains a separation device ( 54 ) which causes part of the gas outflow from the pyrolysis arrangement to be vented and the remaining part of the gas outflow onto a column of the gas chromatograph is transferred. 7. A method for a multidimensional on-line analysis of samples containing non-volatile components, comprising the steps:
Separating the samples into fractions of interest;
direct (on-line) transfer of the fractions into a pyrolysis arrangement;
Pyrolysis of the transferred fractions to produce volatile fragments;
direct (on-line) transfer of the volatile fragments into a gas chromatograph; and
Separation of the volatile fragments by chromatography and detection of the separated fractions. 8. The method of claim 7, wherein the sample is a polymer sample, which is characterized by a size Exclusion chromatograph is separated to Information about molecular weight / size too deliver a fraction of the chromatographed Sample is pyrolyzed and the volatilized Components of the pyrolysis product using of a gas chromatograph to be separated Information about molecular weight / size versus to get the composition. 9. The method of claim 7 or 8, wherein the first Overpass step providing ge separated sample and rinse loops and one subsequent connection of the sample and rinse grind together. 10. The method of claim 7, 8 or 9, wherein the second transfer step venting min at least part of the volatile fragments that are generated in the pyrolysis. 11. An auto-injector device comprising:
a transfer arrangement for receiving a sample containing a low volatility ent;
a pyrolysis arrangement in conjunction with the transfer arrangement for generating volatile fragments which are characteristic of the low-volatility constituent from said sample and a gas chromatograph for recording at least a part of the volatile fragments from the pyrolysis arrangement and for analysis the fleeting fragments. 12. Chromatography device for a multidimensional on-line analysis of compositions containing non-volatile components, comprising:
a size exclusion chromatograph;
a shut-off device for receiving fractions which are eluted from the size exclusion chromatograph;
eie pyrolysis arrangement in connection with the shut-off device for generating volatile fragments which are characteristic of the non-volatile constituents from the fractions and
a gas chromatograph for recording at least a part of the fragments from the pyrolysis arrangement for analysis of the volatile fragments.