FR2944107A1 - AUTOMATIC FEEDING DEVICE OF A CHROMATOGRAPH AND METHOD FOR CARRYING OUT SAID METHOD - Google Patents

Abstract

The present invention relates to a device (1) for automatically feeding a chromatograph (4) for the physicochemical characterization of a material by reverse gas chromatography, characterized in that it comprises an injection unit (2) provided with a magazine (3) containing a plurality of tanks in which probe molecules of different types are stored, a carrier fluid circuit (8) having at least one sample section (82) passing through said magazine (3) and a direct supply section (81) disposed in shunt of said sample section (82), selective distribution means (22 to 26) for the probe molecules in at least a portion of said carrier fluid for supplying said chromatograph (4) and automatic control means (7) of the selective distribution means as a function of the determined experimental conditions and the results of said chromatograph (4).

Description

AUTOMATIC FEEDING DEVICE OF A CHROMATOGRAPH AND METHOD FOR THE IMPLEMENTATION THEREOF

Technical Field: The present invention relates to a device for automatically feeding a chromatograph for the physico-chemical characterization of a material by reverse gas chromatography, comprising a unit for injecting a carrier fluid containing probe molecules and means analyzing the results from said chromatograph to determine at least one physicochemical parameter characteristic of said material.

The invention also relates to a method of physico-chemical characterization of a material by inverse gas chromatography for implementing said device defined above.

Prior art:

The techniques of analysis by "reverse gas chromatography" are well known and make it possible to carry out physicochemical measurements of any type of material. It is thus possible to characterize the surface properties of solids in the form of powders, fibers or plates as well as the physicochemical properties of polymers. The surface properties of a material are particularly important because they will determine the characteristics of adhesion, corrosion, adsorption, dissolution, aging, etc. said material. Thus, the control of the surface properties ensures the control of the properties of a material.

The principle of inverse gas chromatography (CGI) is simple. It is based on adsorption, namely the properties of a material to retain molecules of a gaseous carrier fluid. This analytical technique is widely described in the J. R. Conder and C. L. Young publication Physico-Chemical Measurement by Gas Chromatography Wiley, New York, 1979. The analyte material is used as a stationary phase to fill a chromatographic column. Physico-chemical measurements are performed by injecting molecules known as probe molecules, known and selected according to the information sought. The desired characteristics are determined from the behavior of these probe molecules. Compared to analytical chromatography, the respective roles of the stationary phase and the mobile phase are therefore reversed. This resulted in the name "reverse gas chromatography" (CGI) given to this technique.

The CGI is mainly practiced according to two methods: infinite dilution (DI) or finite concentration (CF). The infinite dilution method is by far the most widespread. It is based on the injection of extremely diluted quantities of probe molecules.

This extreme dilution makes it possible to neglect the interactions between the probe molecules during the chromatographic process and to attribute the origin of the measured retention or adsorption time only to the interactions exchanged between the probe molecules and the analyzed stationary phase of the material.

The validity of the results obtained for infinite dilution measurements therefore depend on the respect of this hypothesis. It is therefore necessary to verify, during analysis, that the probe molecules are well injected at infinite dilution. The difficulty arises from the fact that, at a given measurement temperature, the notion of infinite dilution varies according to the stationary phase and the injected probe molecule. However, the infinite dilution measurements consist in injecting up to twenty different probe molecules by analysis. Verification of the respect of the infinite dilution is carried out by injecting very small and variable amounts of probe molecules and then controlling that the measured retention or adsorption time does not vary according to the quantity injected.

To date, there is no specific automatic injector to achieve this infinite dilution. This type of analysis is therefore performed by an operator who is responsible for performing the injections and verifying compliance with the infinite dilution conditions. This work is long and tedious. Often, the operator is freed from it because he does not have the adapted verification tool, or simply for lack of time. This results in unreliable results, but interpreted as if they were. The lack of automation for the CGI technique has limited the development of this technique, reserving it to specialists.

Presentation of the invention

The present invention aims at overcoming these drawbacks by proposing an automatic feed device for a chromatograph and a process for the physico-chemical characterization of a material by inverse gas chromatography making it possible to reach infinite dilution and to control it in order to to increase the reliability and the productivity of this analysis technique, accessible to non-specialists.

For this purpose, the invention relates to an automatic feeding device of the kind indicated in the preamble, characterized in that said injection unit comprises a magazine containing a plurality of tanks in which are stored different probe molecules, a fluid circuit. carrier comprising at least one sampling section passing through said magazine and a direct feed section disposed in shunt of said sampling section, means for selectively distributing the probe molecules in at least a portion of said carrier fluid to feed said chromatograph and means automatic control of said selective distribution means according to determined experimental conditions and according to the results of the chromatograph.

Each reservoir of the magazine advantageously comprises a sampling chamber located in its upper part to take only the molecules probes in the vapor state, this sampling chamber being connected to the sampling section of said carrier fluid circuit by an inlet valve and an outlet valve.

In a preferred embodiment, these inlet valves and outlet valves are respectively grouped into an inlet common distribution valve and a common outlet distribution valve provided with a number of channels equal to the number of reservoirs plus one, which may consist of solenoid valves.

Preferably, the injection unit comprises a dilution chamber disposed downstream of the magazine, associated with a sensor coupled to the control means for modifying the value of the dilution of the probe molecules in said carrier fluid by addition of pure carrier fluid. The dispensing means may comprise at least one dispensing valve provided with a plurality of channels for, in a first position of the valve, feeding said carrier fluid chromatograph containing a predetermined quantity of probe molecules and in a second position of the valve, feeding said pure carrier fluid chromatograph, said valve being motorized and controlled by said control means.

Preferably, the dispensing valve comprises an exhaust towards the atmosphere supplied by the carrier fluid containing probe molecules, so that, in said second position of the valve, the exhaust path is in series with a calibrated inner loop. and in said first position of the valve, the calibrated inner loop, filled with a predetermined amount of carrier fluid containing the probe molecules, is in series with said chromatograph. This dispensing valve may have six lanes. For this purpose also, the invention relates to a method in which a type of probe molecules is selected in a magazine containing a plurality of probe molecules of different types, using selective distribution means for feeding said chromatograph, and is automatically controlled. the selective distribution means according to determined experimental conditions and results from said chromatograph.

Preferably, a series of measurements is carried out with said type of probe molecule selected by increasing the dilution to reach an infinite dilution determined by the invariability of the retention time of said material as a function of the injected quantities of carrier fluid containing said type of molecules probes.

The series of measurements can be repeated with the other types of probe molecules contained in said magazine to determine other physicochemical parameters characteristic of said material.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention and its advantages will become more apparent in the following description of an embodiment given by way of non-limiting example, with reference to the appended drawings, in which: FIG. 1 is a block diagram of FIG. an automatic feeding device according to the invention coupled to a standard chromatograph; FIG. 2 is a block diagram of the injection unit entering the equipment of FIG. 1; FIG. schematic view from above of the probe molecule magazine entering the injection unit of FIG. 2,20; FIG. 4 is a schematic sectional view of the magazine of FIG. 3; FIGS. 5A and 5B are diagrams of FIG. principle of operation of the dispensing valve of Figure 2 in two positions, and - Figure 6 is an operating diagram of the control means. Illustrations of the invention and best way to achieve it:

With reference to FIG. 1, the automatic feeding device 1 according to the invention is intended to feed a standard type chromatograph 4 for the physicochemical characterization of a material by infinite dilution gas chromatography (CGI) ( DI). The chromatograph 4 comprises in known manner at least one column 5 containing the material to be analyzed and in which a carrier fluid is injected by an injector (not shown) of known type automatically fed said device 1. The chromatograph 4 also comprises detection means 6 of the probe molecule fraction adsorbed by said material during a defined time interval and the results obtained are generally represented in the form of a chromatogram.

The automatic feed device 1 comprises at least one injection unit 2 of a carrier fluid containing selected probe molecules in a magazine 3 of different types of probe molecules, and programmable control means 7 of the control unit. injection 2 as a function of predetermined and programmed experimental conditions, and as a function of the detection means 6, as well as means for analyzing the results of said detection means 6 to determine at least one characteristic physicochemical parameter of said material . The predetermined experiment conditions can be among others the measurement temperature, the flow rate of the carrier fluid, the length of the column 5 of the chromatograph 4, the quantity of the material contained in the column 5, etc. 5 Thus, the equipment of Characterization associating the automatic feeding device 1 according to the invention to a chromatograph 4 makes it possible to measure multiple physico-chemical parameters of the materials, such as: the variation of free interaction enthalpy (AG) between probe molecules and material the interaction enthalpy variation (AH) between probe molecules and material, the interaction free entropy variation (AS) between probe molecules and material, the surface energy (ysd ysa) surface nanoroughness, surface cleanliness, surface acid-base character, glass transition temperatures (Tg), Hansen solubility parameters (HSP).

The injection unit 2 comprises, in the example shown in FIG. 2, selective fluid distribution means provided with solenoid valves 21 to 25 and a six-way distribution valve 26, a dilution chamber. , a pressure sensor 28, a flow control and a store 3 of probe molecules (Ms) of different types. More specifically, the injection unit 2 is connected upstream to a storage tank (not shown) of carrier fluid consisting for example of a neutral carrier gas, such as helium (He), nitrogen (N2 or the like, and downstream to the chromatograph injector 4 via the six-way dispensing valve 26. It comprises a carrier fluid circuit 8 provided with two parallel sections, namely a direct supply section 81 connected directly to the distribution valve 26 and a sampling section 82 passing through the store 3 via the solenoid valves 21 to 25. magazine 3 is short-circuited by a bypass section 83. The solenoid valves 21 to 25 and the six-way distribution valve 26 are controlled by the control means 7.

This injection device 2 makes it possible to inject small quantities of carrier fluid containing a type of probe molecule chosen from a number X of different types of probe molecules. The probe molecules are stored in a tank or flask in which they are in the liquid state and in the gaseous or vapor state. It is the probes molecules in the vapor state that the carrier fluid comes to collect, entrain and inject in the chromatograph 4. We therefore make a mixture of gases (carrier gas + molecules probes in the vapor state) and we play on the dilution of these probe molecules until reaching an infinite dilution.

In the example shown in FIG. 3, the magazine 3 has twenty five locations for receiving twenty five reservoirs 30 of probe molecules of twenty-five different types, it being specified that a complete characterization of a material by CGI may require about 20 different probe molecules. The reservoirs 30 may consist of standard vials having a capacity of 2 ml (see Fig. 4) or any other equivalent container. Each slot has an input E connected to an input distribution valve 22 and an output S connected to another output distribution valve 23. The type of probe molecules to be injected is selected by choosing the position of the corresponding valves 22 and 23. To facilitate control, the distribution valves of the magazine 3 are grouped into common input and output distribution valves 22, each having twenty-six lanes, ie a number of lanes equal to the number of tanks 30 plus one lane. connection to the circuit (see Fig. 2 and 3). These are preferably solenoid valves, but any other equivalent means may be suitable.

Referring to Figure 4, each location comprises a sampling chamber 31 into which the inlet E and the outlet S of the carrier fluid.

Each reservoir 30 is mounted between a lower plate 32 for holding said reservoirs 30 and an upper plate 33 comprising said sampling chambers 31 which open into the upper part of the reservoirs 30 in order to collect the probe molecules only in the vapor state. The seal between the opening of the reservoirs 30 and the upper plate 33 is provided by seals 34 and / or by a conical connection or the like, and by a mounting pressure exerted on each reservoir 30 during the assembly of the two plates. lower 32 and upper 33.

The magazine 3 is maintained at a constant temperature, for example 22 1 ° C., the constancy of the temperature ensuring the constancy of the quantities injected. To guarantee the maintenance of this temperature, the magazine 3 can be placed in a thermally regulated enclosure, or any other equivalent means can be used.

The injection unit 2 also allows the injection of methane (CH4) via a three-way solenoid valve 24 for the determination of the dead volume of the equipment (material sample in the column + chromatographic circuit) which corresponds to an invariable data item. which is taken into account in the measurements and which is deducted retention times. The methane is stored in a container 29 provided for this purpose.

The dilution chamber 27 makes it possible to vary the quantities injected by diluting the quantities of carrier fluid containing the probe molecules present in the chamber 27 by addition of pure carrier fluid via the bypass section 83 and the solenoid valves 22 and 23. The presence of a pressure sensor 28 controls the amount of carrier fluid added.

The actual injection is carried out by means of a specially designed six-way valve 26 (see Fig. 5A and 5B) controlled by the control means 7. The connection of the six channels V1 to V6 is performed as follows: V1 connected to the column 5 of the chromatograph via an injector, V2 connected to a calibrated internal loop B, V3 connected to an exhaust to the atmosphere A, V4 connected to the sampling section 82, V5 connected to the loop Calibrated internal B, and V6 connected to the direct supply section 81. When the valve 26 is in position 2 (see Fig. 5B), the channels V6 and V1 communicate supplying the column 5 with pure carrier fluid (He), while that the channels V4, V5, V2 and V3 communicate ensuring the filling of the internal loop calibrated B carrier fluid containing a type of probe molecules chosen (He + Ms). When the valve 26 passes to position 1 (see FIG 5A), the channels V4 and V3 communicate putting the carrier fluid containing probe molecules (He + Ms) into the atmosphere, while the channels V6, V5, V2 and V1 communicate supplying the column 5 carrier fluid containing probe molecules (He + Ms) in a predetermined amount. The calibrated internal loop B allows for example the injection of 15 L of carrier fluid containing probe molecules (He + Ms). The injected quantities of carrier fluid containing probe molecules are controlled by the temperature of the magazine 3, the flow rate of the carrier fluid via the solenoid valves 21 and 25, and the opening times of the common inlet and outlet valves 22. .

The injection unit 2 is coupled to the control means 7 comprising a PC-type computer or the like, specific electronic I / O cards, the set being controlled by a dedicated software L for the acquisition of the chromatographic data, their automatic processing and archiving them in a BD database. The injection unit 2 combined with the control means 7 is characterized by its ability to adjust the injected quantities of probe molecules in the carrier fluid until the invariance of the retention time is obtained as a function of the quantities injected allowing to reach the conditions of infinite dilution (DI).

Consequently, the control means 7 have multiple functions: the control of the automatic injection unit 2, the acquisition of the data of the chromatograph 4 (chromatograms), the management of the predetermined and programmed experimental parameters, the automatic detection of the end of a measurement (injection), - the automatic integration of the chromatogram and the calculation of the net retention volume, - the archiving of chromatograms and experimental data in a database, - the possibility of reprocess manually, at any time, any chromatogram of the database, - the ability to recognize if the infinite dilution criteria are respected and to make the decision which results from it, - the possibility of following a predefined protocol (list of molecules probes ) or to choose itself the probe molecules according to the analyzed material, - the calculation of the physicochemical data resulting from the measured net retention volumes és, - the generation of a final analysis bulletin.

FIG. 6 illustrates the automated operation of the injection unit 2 thanks to the control means 7 in the form of a diagram in which: x corresponds to the number of different types of probe molecule of the measurement protocol, this number being at least 3 and less than or equal to 20. N corresponds to the number of the type of probe molecules and may be equal to 1 to 25 (according to the number of reservoirs 30 contained in the magazine 3). n corresponds to the number of measurements made with the same type of probe molecules until reaching the infinite dilution and is at least equal to 3.

At the start of a measurement cycle, the measurement protocol is defined, namely the number and type of probe molecules, the measurement temperature, the flow rate of the carrier fluid, the quantity and the nature of the material contained in column 5 of the chromatograph 4, etc. A first type N of probe molecules is chosen and a quantity of this type of probe molecule is taken. It is injected into the chromatograph 4 and the results are recovered in the form of a chromatogram which is stored in the database BD. The chromatogram is analyzed and if an adsorption peak does not appear, it means that the injected amount of probe molecules was insufficient. The measurement is repeated by taking a larger quantity of the same type of probe molecules. If an adsorption peak appears, a mathematical treatment of the chromatogram is carried out to determine in particular the retention time, the retention volume, the peak area, the peak center of gravity, the offset between the peak peak and its peak. center of gravity, etc. and these results are stored in the database BD. We verify if these results are representative of an infinite dilution. If not, the measurement is repeated by diluting the quantity of probe molecules by addition of pure carrier fluid. If so, it is checked whether with the same type of probe molecules at least three measurements have been made n. If not, the measurement is repeated with the same dilution or not. These measurement loops continue automatically until they reach the infinite dilution conditions for each type N of probe molecules, and for the set x of the different types of probe molecules determined in the measurement protocol. Then the results are edited in the form of a bulletin for example and stored in the database BD.

The entire program is written for example in C language with a programming tool for example "LabWindows CVI" of National Instrument. The database DB for example "MySQL" is integrated in the software L and allows to memorize the measurement protocols, the corresponding results, the chromatograms. It thus authorizes the reprocessing of any measurement made, as well as the search for measurement protocols implemented. The control of the injection unit 2 is carried out thanks to a specific electronic I / O card having thirty two outputs mounted in a PC-type computer and the data acquisition is performed by means of an I / O acquisition card. mounted in the same computer. It allows you to manage four acquisition channels simultaneously. Of course, other embodiments are possible.

Possibilities of industrial application: It is clear from this description that the invention makes it possible to achieve the goals set. In particular, the combination of the injection unit 2 and the control means 7 makes it possible to perform physico-chemical measurements of materials with a very low concentration of probe molecules (Infinite Dilution), and to confer on the whole of the characterization equipment automation, autonomy, reliability and reproducibility.

In the example shown, the automatic feeding device 1 is sized to allow the individual injection of a minimum of twenty five molecules of different types of probes and interchangeable as needed. In addition, it is adaptable to all types of gas chromatographs. The control means 7 provide the link between the different modules of said device 1.

The present invention is not limited to the embodiment described but extends to any modification and variation obvious to a person skilled in the art while remaining within the scope of protection defined in the appended claims.

Claims (11)

Revendications1. Device (1) for automatically feeding a chromatograph (4) for the physicochemical characterization of a material by reverse gas chromatography, comprising an injection unit (2) for a carrier fluid containing probe molecules and means for analyzing the results from said chromatograph (4) to determine at least one characteristic physicochemical parameter of said material, characterized in that said injection unit (2) comprises a magazine (3) containing a plurality of reservoirs (30) ) in which are stored probe molecules of different types, a carrier fluid circuit (8) having at least one sampling section (82) passing through said magazine (3) and a direct supply section (81) disposed in a bypass said sampling section (82), means (22, 23, 26) selectively distributing the probe molecules in at least a portion of said carrier fluid to feed said chromatograph (4) and means automatic control (7) of said selective distribution means according to determined experimental conditions and results of said chromatograph (4). 2. Device according to claim 1, characterized in that each reservoir (30) of said magazine (3) comprises a sampling chamber (31) located in its upper part so as to collect only the probe molecules in the vapor state, this sampling chamber being connected to the sampling section of said carrier fluid circuit by an inlet valve (22) and an outlet valve (23). 3. Device according to claim 2, characterized in that the inlet valves and the outlet valves of said magazine are respectively grouped in a common inlet distribution valve (22) and a common outlet distribution valve (23). provided with a number of channels equal to the number of tanks plus one. 149. A process for physicochemical characterization of a material by inverse gas chromatography for implementing said device (1) according to any one of the preceding claims, in which a carrier fluid containing probe molecules is injected into at least one column (5) of a chromatograph (4) containing said material to be analyzed, detecting the fraction of probe molecules adsorbed during a defined period of time and analyzing the results obtained to determine at least one physicochemical parameter characteristic of said material, characterized in that a type of probe molecules is selected in a magazine (3) containing a plurality of probe molecules of different types, using selective distribution means (22, 23, 26) for feeding said chromatograph (4) , and in that said selective distribution means (22, 23, 26) are automatically controlled as a function of experimental conditions. determined and results of the chromatograph (4). 10. The method of claim 9, characterized in that one carries out a series of measurements with said type of probe molecules selected by increasing the dilution to reach a so-called infinite dilution determined by the invariability of the retention time of said material depending injected amounts of carrier fluid containing said type of probe molecules. 11. The method of claim 10, characterized in that said series of measurements is repeated with the other types of probe molecules contained in said magazine (3) to determine other physicochemical parameters characteristic of said material.25References 1. Device (1) for automatically feeding a chromatograph (4) for the physicochemical characterization of a material by reverse gas chromatography, comprising an injection unit (2) for a carrier fluid containing probe molecules and means for analyzing the results from said chromatograph (4) to determine at least one characteristic physicochemical parameter of said material, characterized in that said injection unit (2) comprises a magazine (3) containing a plurality of reservoirs (30) ) in which are stored probe molecules of different types, a carrier fluid circuit (8) having at least one sampling section (82) passing through ledi t store (3) and a direct supply section (81) disposed in derivation of said sampling section (82), selective distribution means (22, 23, 26) of the probe molecules in at least a portion of said carrier fluid for supplying said chromatograph (4) and automatic control means (7) for said selective distribution means according to determined experimental conditions and the results of said chromatograph (4). 2. Device according to claim 1, characterized in that each reservoir (30) of said magazine (3) comprises a sampling chamber (31) located in its upper part so as to collect only the probe molecules in the vapor state, this sampling chamber being connected to the sampling section of said carrier fluid circuit by an inlet valve (22) and an outlet valve (23). 3. Device according to claim 2, characterized in that the inlet valves and the outlet valves of said magazine are respectively grouped in a common inlet distribution valve (22) and a common outlet distribution valve (23). provided with a number of channels equal to the number of tanks plus one. 14 4. Device according to claim 3, characterized in that said common valves input distribution (22) and outlet (23) consist of solenoid valves. 5. Device according to any one of the preceding claims, characterized in that said injection unit (2) comprises a dilution chamber (27) disposed downstream of said store. (3) associated with a sensor (28) coupled to said control means (7) for modifying the value of the dilution of the probe molecules in said carrier fluid by addition of pure carrier fluid. 6. Device according to any one of the preceding claims, characterized in that said dispensing means comprise at least one distribution valve (26) provided with a plurality of channels (V1 to V6) for, in a first position of the valve, to supply the chromatograph (4) carrier fluid containing a predetermined amount of probe molecules and in a second position of the valve, supplying the chromatograph (4) pure carrier fluid, said valve being motorized and controlled by said control means (7). 7. Device according to claim 6, characterized in that said dispensing valve (26) further comprises an exhaust (A) to the atmosphere supplied by the carrier fluid containing probe molecules, and in that in said second position of the valve, the exhaust path (A) is in series with a calibrated inner loop (B), and in said first position of the valve, the calibrated inner loop (B), filled with a predetermined quantity of carrier fluid containing probe molecules, is in series with said chromatograph (4). 8. Device according to claim 7, characterized in that said distribution valve (26) comprises six channels. 9. Process for the physicochemical characterization of a material by inverse gas chromatography for implementing said device (1) according to any one of the preceding claims, in which a carrier fluid containing probe molecules is injected into at least one column (5) of a chromatograph (4) containing said material to be analyzed, detecting the fraction of probe molecules adsorbed during a defined period of time and analyzing the results obtained to determine at least one physicochemical parameter characteristic of said material, characterized in that a type of probe molecules is selected in a magazine (3) containing a plurality of probe molecules of different types, using selective distribution means (22, 23, 26) for feeding said chromatograph (4) , and in that said selective distribution means (22, 23, 26) are automatically controlled according to experimental conditions. determined and results of the chromatograph (4). 10. The method of claim 9, characterized in that one carries out a series of measurements with said type of probe molecules selected by increasing the dilution to reach a so-called infinite dilution determined by the invariability of the retention time of said material depending injected amounts of carrier fluid containing said type of probe molecules. 11. The method of claim 10, characterized in that said series of measurements is repeated with the other types of probe molecules contained in said magazine (3) to determine other physicochemical parameters characteristics of said material.