JPH0332023B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The method of controlling a small volume of liquid sample according to the invention to a chromatographic analyzer, in particular a high-resolution gas chromatograph analyzer and a thin layer chromatograph analyzer having a capillary column or a micropack column. and how to introduce it in a reproducible manner. According to the invention, in order to obtain maximum reliability and reproducibility with extremely small sampling volumes, sample containers are used with pipette-like or nozzle-like exit necks of very small diameter; Liquid placed in the container is delivered with at least one pressure pulse controlled in time and/or amplitude to determine a correspondingly controlled amount of liquid exiting the outlet neck. This pressure pulse can be an aerodynamic pulse applied directly to the liquid sample in the container, or a mechanical pulse applied to the liquid sample by a magnetostrictive or piezoelectrically acting device.

Microsyringes used for chromatographic analysis are generally of the type with a calibrated body (bodies calibrated to sample volumes ranging from 0.2 to 10 microliters) or with a needle that has a small internal volume. It is assumed that the needle is calibrated and is either of the type in which a piston penetrates the needle. The latter microsyringes are capable of handling small sample volumes in a reliable and reproducible manner, but only within certain limits, especially around 200-300 nanoliters (2-3 x 10 ^-7 liters). This is within the lower limit of . Below this limit, due to the high surface tension of the liquid and the relatively low velocity of the piston movement, the droplet formed at the tip of the needle is It becomes difficult to fall from here. Additionally, a poor seal between the piston and the calibration needle will adversely affect the accuracy of this quantity.

Another known system is a sampling system commonly used in laboratories called a "pipette system." This involves filling a calibrated tube with a controlled amount of the liquid to be transferred by sucking it into the mouth, and then closing the mouthpiece to retain the liquid within the tube. The mouthpiece is then opened to inject the liquid into the receiving container. Methods of sampling or transferring such predetermined amounts of liquid are well known and have been used in gas chromatographic analysis. According to the literature, the lower limit of the amount is 20-50 nanoliters (2-50 nanoliters).
5 × 10 ^-8 liters) [Gas Phase Chromatography, by R. Kaiser, published by Butterworths, 1963, Volume 1, No. 90-95.
(see page), quantities that can usually be measured are only very approximate values.

Therefore, the lower limit is approximately 50 or
It can be considered to be between 200 nanoliters (5-20×10 ^-8 liters). Below this, reliable and reproducible sampling cannot be performed using a microsyringe or micropipette.

Furthermore, in the case of pipettes, and often microsyringes, if the gaseous fluid between the piston and the sample liquid is not completely removed, the gas that forces the liquid out of the pipette will enter the capillary column. This often results in the problem of having to select and use a gas that does not affect the analysis.

The above-mentioned quantitative constraints often require additional operations in order to introduce a relatively large amount of sample into the capillary column of a chromatographic analyzer. Particularly when direct injection is performed without vaporization (on-column), the sample often has to be diluted with very high dilution ratios (approximately 1:100,000 or more). This manipulation involves difficulties in the accurate analysis of the sample and the possibility of introducing variations in the conditions of the sample.

In other cases, a so-called splitting operation is necessary. This means that a large percentage of the volume delivered to the syringe is lost before introduction into the column, and such an operation may involve an even higher risk of discrimination.

Therefore, it is an object of the present invention to reproduce very small liquid samples, for example 10 picoliters (1×10 ^-11 liters) to 50 nanoliters (5×10 ^-8 liters), with the same sampling conditions and the same samples. The object of the present invention is to provide a method for sampling into a chromatographic analyzer in a possible manner.

Another object of the invention is to simultaneously introduce other substances, whether liquid or gaseous, into the chromatographic analyzer in order to displace this sample from the sampling vessel upon the introduction of a very small volume of liquid sample. The purpose of the present invention is to provide a method as described above that does not require the use of a computer.

Yet another object of the invention is that the above-mentioned operating in special conditions that the injection of a quantity of substance into the chromatographic analyzer is carried out with maximum reliability, accuracy and reproducibility during the injection step itself. We are here to provide you with a method.

That is, the present invention provides a chromatographic analysis system, particularly a high-resolution gas chromatography analysis system or a thin layer chromatography analysis system, in which 10 to 50
In a method for sampling very small amounts of liquid samples, such as nanoliters, the maximum dimension 1 or
Provide a sample container with a pipette- or nozzle-shaped neck serving as an outlet for an opening of 100 microns, preferably 1 to 30 microns, and a volume larger than the volume to be sampled, and place the sample into this sample container. filling the outlet opening of the neck with a larger amount of sample to form a meniscus of sample liquid at the outlet opening of the neck, and before or after filling the sample container or a portion thereof, injecting the sample into a chromatographic analysis system. Introduce it into the equipment that will
at least one pressure pulse having a pressure value sufficient to overcome the surface tension of the liquid sample at the outlet and a duration limited in time according to this pressure value and the quantity to be sampled;
Taking into account the outlet opening dimensions, pressure pulse amplitude, sample characteristics and number of pulses, the very small amount of sample is injected into the sample injector by giving the liquid in the sample container the outlet of the sample container. abruptly reducing the pulse pressure to a value below a pressure sufficient to overcome the surface tension of the liquid at the aperture and abruptly interrupting sample injection to prevent a droplet from forming and remaining at the neck; A chromatographic analysis sample collection method is characterized in that:

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to preferred embodiments illustrated in the accompanying drawings.

As mentioned above, the present invention relates to a method for sampling a liquid sample into a chromatographic analysis system, and this method is particularly applicable to an experimental chromatographic analysis system, in which a capillary column is provided to sample a liquid sample without premature evaporation. It is applied to high-resolution gas chromatography analysis systems or thin layer chromatography analysis systems that can perform direct on-column injection. In particular, direct injection chromatographic analysis systems are well known, in which a liquid sample is injected directly into the front of the column, and then moved along the column by a carrier gas, while at the same time vaporizing the sample. is being transformed. The method according to the invention, particularly in chromatographic analysis systems of the type described above, does not require the dilution measures required in conventional methods to obtain the correct amount of injected sample, and the analysis can be carried out within the chromatographic analysis system. This makes it possible to inject as little liquid sample as possible.
The method exemplified herein is capable of injecting amounts exceeding these amounts, and in this way, liquid samples with amounts in the range of 10 picoliters to 50 nanoliters, i.e., unthinkable with conventional analytical systems, can be injected. It is particularly suitable for reliably and reproducibly injecting small amounts of liquid samples that otherwise would not be possible.

The method of the invention is based on the use of containers for liquid samples. This container is made of any suitable material and has a volume larger than the volume of the sample actually subjected to analysis. For example, the material may be glass, fused silica, or any other material, and the shape may be pipette-like, needle-like, or any other suitable shape.

The essential requirement for this container is that the container has a maximum dimension (in this case diameter d) in the range of 1 to 100 microns, preferably 1 to 30 microns, as shown at 10 or 12 in FIG. having a neck with an outlet having a range of dimensions. This neck can be nozzle-shaped, as shown at 14 in FIG. This neck preferably has a diameter d of 10 to 30 microns. The neck may also preferably be in the form of a micropipette, as shown at 16 in FIG. 1, having a diameter d of 1 to 20 microns. 1st
The container 10 or 12 illustrated in the figure contains the required amount to be drained from the neck 14 or 16 by any conventional method, such as by syringe, gravity, capillary tube, or any other means, to be used for analysis in a chromatographic analysis system. A larger amount of liquid 17 is filled. Once the sample liquid 18 has been delivered to the container 10 or 12, especially in the case of a container 12 with a pipette-like end, the liquid has descended sufficiently to reach the neck 14 or 16, where it forms a meniscus. It is necessary to confirm that it is formed. Under these conditions, the cervical dimensions are reduced, so
The surface tension of the liquid prevents the liquid from forming droplets and falling down the neck. This obviously provides that the neck 14 or 16 does not touch foreign bodies such as the walls of the gas chromatographic analysis column. If it is touched, the liquid will flow out of the column. Cervical 1 as mentioned above
4 or 16, by applying pressure directly or indirectly to the liquid 18 as schematically indicated by arrow 20 in FIG. That's what I do. This pressure is determined by the amplitude as shown in Figures 2 and 3, taking into account that the amount of liquid released depends on the amplitude, i.e. the value of the pulse pressure, the duration of this pulse itself and the number of such pulses. It is controlled both physically and temporally.

As can be seen in Figures 2 and 3, this pulse has the form of a step, the falling part, the return of the pressure to zero, being as vertical as possible and the peak at this stage. It is very important to be able to avoid the formation of droplets in portions 14 or 16. This is because, if such droplets are formed and remain, they will completely change the measurement results of the injected sample. In the case of Figure 2, the pressure pulse is an aerodynamic pulse and has the value P ₁
reach. This value P ₁ is in any case the neck 14
Or the value must be higher than that required to overcome the surface tension of the liquid at 16. Select the duration Δt of this pulse in relation to the pressure value P ₁ . This duration can vary from about 1 millisecond to about 1 second to achieve a predetermined amount of ejected liquid.

The pressure value can range from 1 to 10 atmospheres. It is also possible to use several pulses with short duration. However, in order to ensure reproducibility of sampling, it is very important to minimize the dead space, ie the gas volume affected by each pressure pulse.

The situation illustrated in FIG. 3 is that which occurs in the case of pressure pulses produced by magnetostrictive or piezoelectric means. In this case, the time Δt is extremely short, and the resonant frequency of the laminated core forming the magnetostrictive device, or 10
While accommodating frequencies of piezoelectric materials ranging from 100 KHz to 100 KHz, control of the amount emitted with each pulse can be achieved by varying the amplitude of the electrical pulses applied to the device. This pressure value is in any case one or several orders of magnitude higher than the value required in the aerodynamic case. An apparatus for carrying out the method of the invention by means of aerodynamic pulses is schematically illustrated in FIG. In this figure, a receiving container 10 of the type exemplified on the left in FIG. It is removably fixed by a gas mat 24 compressed by a nut. The support block 26 has a duct 28 for supplying pressurized gas, for example air. There is also a further duct 30 in the block 26, which can be closed by a locking element 32. A sample 18 is supplied to the container 10 . The locking element 32 includes, for example, a metal projection 33, which makes it possible to reduce the dead space to a minimum.

Duct 28 connects air source 34 to air source 34 in any known manner.
It is connected to a circuit that supplies pressurized air coming from the This circuit consists of a pressure controller 36 and an electric valve 38.
includes. The opening time of this electric valve 38 can be controlled by a known device 40. The duct 42 is located between the electric valve 38 and the block 26 and preferably has a very small internal diameter to minimize so-called dead volume. This dead volume is the air volume that exists between the valve 38 and the upper meniscus of liquid 18 in volume 10. Reducing this dead volume causes the pressure to drop rapidly at the end of the pulse, causing the vessel 1
It is very important to avoid droplets forming and remaining at the outlet of the 0.

The apparatus of FIG. 4 is supplied with a larger amount of sample than is to be injected into the gas chromatographic analysis system, for example by means of a conventional syringe, through the opening with the locking element 32 removed. Once this supply has been made, the opening is closed, the container is introduced into the chromatographic apparatus, and the valve 38 is opened for a time controlled by the apparatus 40 to generate a pressure pulse having a value controlled by the pressure sensor 36. cause it to occur. In this way a small liquid jet is formed at the outlet neck 1
From 4, it comes out in the form of small drops. If the type of liquid and neck diameter are the same, the farther from the outlet neck 14 the greater the pressure value.

The sampling device illustrated in FIG. 5 is operated by a piezoelectric device. In a portion of this sampling device, the elements for forming and ejecting the drop jet are substantially similar to known jet-on-demand ink drop printing devices. This includes as a main component a container 44, which is not necessarily cylindrical, for example made of glass or fused silica, and in which the sample to be injected into the column is introduced, for example, from the top and into the bottom. It is ready to be filled.

The container 44 terminates at its lower part in a calibrated nozzle 14, as described above, from which a liquid jet is ejected. At atmospheric pressure, liquid does not flow out of the nozzle 14 due to surface tension.

The container 44 is connected to a piezoelectric transducer 50. This piezoelectric transducer 50
When excited, it causes a sudden change in volume within the container 44, which causes a sudden change in pressure in the liquid therein, causing it to flow out through the nozzle 14 as a calibrated jet of one or more drops. I am forced to do it. A small block 5 made of plastic material, for example, arranged in the immediate vicinity of the nozzle 14.
This transducer 50, housed within 2, is energized by an electrical pulse source 54. This electric pulse, which has the characteristics described above, is supplied to the electrode 51 of the piezoelectric transducer 50 via a circuit 53 having a switch 55. Switch 55 allows the operator to close the circuit and control the release of the jet of drops. Connected to the electrical pulse source 54 is a known device 56 for varying the amplitude of the pulses applied to the transducer 50. Other devices 57 are devices that control the duration of the pulse or series of pulses.

In operation, the container 44 must first be filled with a liquid sample, at least close to the nozzle 14, using, for example, a microsyringe. Transducer 50 generates a pulse or a series of pulses having a predetermined amplitude. During this time, nozzle 14 emits a jet of one or more droplets of sample liquid in a predetermined small amount. This jet is highly directional and its diameter increase is extremely limited, so that it can be inserted, for example, into the column of a chromatographic analyzer via the injection port of a direct injector with a slicing or rotary valve. It can be directed to.

The amplitude of the pulse is controlled by element 56 to provide control of the pressure rise imparted by the pulse. As a result, precise control of the formation of the droplet jet can be obtained, taking into account the nozzle diameter and the properties of the treatment liquid, the first parameters influencing the operating conditions. If other conditions remain unchanged, the emission of a given sample is obtained thanks to the formation of a pulse with a preselected amplitude, so that the emission obtained with a series of pulses is It will depend on the duration of the pulses and thus on the number of pulses forming this pulse train. This is because the duration of each pulse is determined by the characteristics of the transducer.

The device illustrated in FIG. 6 consists of a container or needle 44 having a needle syringe 46 with a piston 48. The needle 44 is introduced into the duct 58 inside the body of an injector 60 of known type with a valve 62 . The injector body is provided with a magnetostrictive device 64 made of nickel that acts on the needle 44. The applied pressure determines the desired amount of sample ejection, independent of the position of the cylinder piston 48, as long as the liquid 18 fills the needle 44 at least partially, i.e. up to its exit neck 14. shall be sufficient for Both in the case of aerodynamic pulses and also in the case of piezoelectric or magnetostrictive mechanical pulses, the method and device according to the invention, when applied to a high-resolution gas chromatograph analyzer having a capillary column, can be used to transport the vessel 10 or 12 and the capillary column 66 back and forth. There are two examples of how to move. First, a first example is shown in FIG. In this FIG. 7, the container 10 or 12 is shown to have an outer diameter that is smaller than the inner diameter of the capillary column 66 or the enlarged end 67 of the capillary column. To this end, the container 10 or 12 is inserted into the injector so that its end can pass through the inlet opening of the capillary column 66.
In this case, the discharge of the liquid sample under the aforementioned conditions is only restricted to ensuring that the neck 14 does not touch anything, especially the walls of the column 66. During and after injection of the sample, a flow of carrier gas is obtained which is directed into the column through the hollow space existing between the column wall and the vessel 10, as indicated by arrow 68.

Conversely, if the capillary column has an inner diameter smaller than or equal to the outer diameter of the container 10 or 12, the capillary column may have an inner diameter smaller than or equal to the outer diameter of the container 10 or 12.
An example is shown in the figure. In this case, the injector body 7
0 has a neck 72 formed therein. This neck preferably has as short an axial length as possible and has a column 66 and a container 10 or 12 on each side.
Place. Container 10 or 12 is preferably housed within a protective member 74 so that container 10 or 1
Let 2 be the seat that hits the wall. In this case, as mentioned above,
() Outlet neck 14 or 1 of container 10 or 12
6 and the column 66, i.e. the distance measured in the axial direction, as short as possible, for example at most 10 mm; and () the neck 14 or 16.
The injection pressure of the jet inward is sufficient to maintain conditions such that there is very little tendency for the jet to widen in diameter, and that the axial alignment of neck 14 and column 66 is perfect. It is desirable to meet these three conditions.

In this case, the supply of carrier gas, which normally enters the column through section 68, is interrupted to ensure that the carrier gas is not unavoidable if the injected sample, especially the injected material, contains substances that are easily evaporated. .

The method exemplified herein is particularly useful for very small diameter capillary columns.

Although the present invention has been described above in detail with reference to preferred embodiments of the present invention as illustrated in the accompanying drawings, the present invention is not limited to these specific embodiments and can be modified in many ways without departing from the spirit of the present invention. Of course it can be done.

[Brief explanation of the drawing]

FIG. 1 is an enlarged vertical sectional view showing two examples of the shape of the outlet of the sample container used in the method of the present invention, and FIGS. 2 and 3 are characteristic diagrams showing examples of the shape of the pressure pulse used in the present invention. , FIG. 4 is a sectional view showing the main parts of a device for sampling by using aerodynamic pulses, and FIGS. 5 and 6 are schematic diagrams showing devices for sampling by pressure pulses obtained with a piezoelectric device or a magnetostrictive device, respectively. cross-sectional view, 7th
Figure 8 is a schematic cross-sectional view showing the position of the sample container outlet in such an apparatus and the end of the capillary column of a high-resolution gas chromatograph analyzer.
9 and 9 are schematic cross-sectional views showing other positions of the sample container and the end of the same capillary column as in FIG. 7. 10, 12... Container, 14, 16... Neck or nozzle, 18... Sample, 22... Locking nut,
24...Gasket, 26...Support block, 2
8... Duct, 30... Duct, 32... Locking element, 34... Pressurized air source, 36... Pressure regulator, 38... Electric valve, 40... Device, 42...
duct, 44...container or needle, 48...piston, 50...transducer, 52...block, 54...electric pulse, 56...device, 60...
...Injector, 62...Valve, 64...Magnetostrictive device,
66...Capillary column, 67...Enlarged part,
70... Injector body, 72... Neck, 74...
...Protection member.

Claims (1)

[Claims] 1. Methods for sampling very small amounts of liquid samples, from 10 picoliters to 50 nanoliters, in chromatographic systems, especially high-resolution gas chromatographic systems or thin layer chromatographic systems, preferably with a maximum dimension of 1 to 100 microns. Provide a sample container with a pipette- or nozzle-shaped neck serving as an outlet for an opening of 1 to 30 microns and a volume larger than the amount to be sampled, and place a larger amount than the amount to be sampled into the sample container. filling the outlet opening of the neck with a sample to form a meniscus of sample liquid, and before or after this filling, the sample container or a portion thereof is introduced into a device for injecting the sample into the chromatographic analysis system. and at least one pressure pulse having a pressure value sufficient to overcome the surface tension of the liquid sample at said outlet and a duration limited in time according to this pressure value and the quantity to be sampled. injecting the very small amount of sample into the sample injection device, taking into account the dimensions, pressure pulse amplitude, sample characteristics and number of pulses, given to the liquid in the sample container;
abruptly reducing the pulse pressure to a value below a pressure sufficient to overcome the surface tension of the liquid at the outlet opening of the sample container and abruptly interrupting the sample injection to form a droplet at the neck; A method for collecting a sample for chromatographic analysis, characterized in that it avoids being left behind.