US3063051A - Gas chromatography - Google Patents

Description

Nov. 6, 1962 E. PALM 3,063,051

GAS CHROMATOGRAPHY Filed April 9, 1959 INVENTOR. E. PALM BY WK United States Patent 3,063,051 GAS CHROMATOGRAPHY Ernst Palm, Uberlingen (Bodensee), Germany, assignor t0 Bodenseewerk, Perkin-Elmer & Co., G.m.b.H., Uberlingen (Bodensee), Germany Filed Apr. 9, 195%, Ser. No. 805,226 6 Claims. (Cl. 346-33) This invention is concerned with a method and a device for the analysis of mixtures by means of gas chromatography.

In analysis 'by means of gas chromatography, a sample mixture in the gaseous or vaporous state is introduced into a stream of an inert carrier gas. This sample is conveyed through an adsorbing substance (separating substance) by the carrier gas stream. The individual components of the mixture undergoing investigation are adsorbed with more or less strong affinity by the separating substance. The time required for flushing a component through the separating substance by means of the carrier gas stream depends on the degree of aflinity with which the respective component is adsorbed. A c0mponent, for instance, which does not interact in any way with the separating substance will pass through the latter with maximum speed determined by the mechanical flow resistance of the apparatus; a substance having infinitely great aflinity for the Separating substance would not pass through it at all. Generally, the different substances of a mixture will appear with more or less delay one after the other at the exit from the separating substance and may be individually recorded.

Normally, a bridge with temperature sensitive resistors is arranged at the exit of the sample cell containing the separating substance, the bridge being so arranged that one arm is immersed in the gas stream. If the emerging stream of gas contains a component in addition to the carrier gas, the thermal conductivity of the gas is changed whereby the bridge is unbalanced. With conventional apparatus, the measured voltage value so obtained is amplified and utilized for the control of a recording device which establishes a diagram on a continuously moving recording chart. In this diagram, the individual components of the mixture appearing one-after the other at the exit of the separating substance can be distinguished as bands. Such a diagram is shown by way of example in FIG. 1 which represents the measured voltage plotted against time.

The reference character t designates the moment at which the experiment starts, i.e., the moment at which the mixture undergoing investigation is introduced into the carrier gas stream. After an interval of time t a substance appears at the exit of the sample cell which has not interacted with the separating substance contained in the cell and which produces a band 1 in the diagram. Such an inert ple. The air band normal test conditions. The different components of the mixture appear after time intervals t t t and produce bands 2, 3 and 4. The period of time up to the moment where these bands appear on the diagram and the height of the bands permits a conclusion as to the nature and the concentration of the components. As can be clearly seen from FIG. 1, the bands show ever increasing width the later they appear.

With a constant speed of feed of the recording chart, there is the disadvantage that substances having a strong adsorption affinity for the separating substance appear only after a relatively long interval of time, causing undesirably long recordings. This, in turn, gives rise to considerable diificulties with regard to the evaluation and filing of such diagrams. In order to eliminate these dissubstance may be air, for exam is almost regularly found under v and the relation t /t 3,053,051 Patented Nov. 6, 1962 advantages, it has been proposed that the speed of the recording chart be varied in inverse proportion to the time period of the experiment. This has the effect of contracting the time axis while at the same time those bands appearing after longer intervals of time are given slopes of greater steepness so that they can be more readily detected.

However, the Well known methods proposed for achieving this end have the disadvantage that the bands of the individual substances will always be recorded at different points of the recording paper, depending on the type of apparatus used and the velocity of flow of the carrier gas. Therefore, gas-chromatographic diagrams obtained from two different apparatus cannot be compared with each other without difiiculty. The evaluation of such diagrams is therefore a rather diiiicult and time wasting job and requires considerable experience in this particular field.

The present invention has therefore for its objects the elimination of these disadvantages and the provision of a system whereby the bands of a gas-chromatographic diagram are always recorded at exactly defined points of the recording paper.

In order to accomplish the above objects, the speed of the recording paper is varied inversely proportional t the duration of the experiment, but the feed motion f the recording paper is only begun when a substance not interacting with the separating substance appears at the exit of the latter.

In order that the speed of the recording chart be inversely proportional to the duration of the experiment, the path length of feed of the recording chart varies with the logarithm of the duration of the experiment, and this is the time interval which has lapsed since the moment the sample was introduced into the carrier gas stream. But since the recording chart only begins to move after the air component has appeared, its length corresponds to the logarithm of the elapsed time of the experiment I minus the logarithm of that time I which passes before the "air band 1 appears. Since the type of the apparatus used, each band will be recorded at an exactly defined point of the recording chart.

The points at which the bands of the different substances appear may be preliminarily marked on the recording chart won a transparent cover sheet corresponding in shape to the recording chart.

For the practical application of the method, an apparatus is used in which a measured value correspond ing to the separated components of interest is recorded on a continuously moving record chart having a speed inversely proportional to the elapsed time of experiment. The apparatus is so designed that the feed motion of the recording chart only star-ts a certain time after a sub-' stance not interacting with the separating substance appears at the exit of the latter.

A further development of the invention allows the sensitivity of the recording to be continuously increased during the experiment. This is done in such a manner that the sensitivity of recording is varied proportionally with the elapsed experiment time. This has the effect of compensating for the flattening of the very late appearing bands. It is then possible, at those points where the bands of the different substances will appear, to print graduated scales on the recording chart or on a corresponding transparent cover sheet. These graduated scales permit the concentrations of the respective substances to be read from the heights of the recorded bands. Evalua for each band is iridependentof.

tion and analysis of gas chromatographic diagrams may these be accomplished without difficulty.

In the preferred embodiment of this invention, a cylinder supporting a recording chart is driven by means of an electric motor running at constant speed, the motor being switched on when the mixture undergoing investigation is introduced into the carrier gas stream. The recording cylinder is driven through a transmission which supplies a speed inversely proportional to the time period elapsed during the experiment. Such transmissions are known in the prior art. Rope drive transmissions equipped with appropriate cam plates, for instance, may be used for this purpose. In order to eliminate the initial speed range in which the driven speed of the transmission should be infinitely great, a clutch may be arranged between the motor and the transmission, the clutch being engaged only after the motor shaft has performed one full revolution. The delay of the paper feed may also be realized by another clutch between the transmission and the recording cylinder. This latter clutch has the function of setting the recording cylinder into action only after the drive shaft of the transmission has performed a certain angular movement the length of path of which can be adjusted. The variation in recording sensitivity is most advantageously obtained by the aid of a logarithmically wound potentiometer coupled with the paper feed motion. The measuring voltage is impressed upon the potentiometer and the voltage for a recording device is tapped from it. The potentiometer is designed as a variable potentiometer by which the full scale sensitivity may e varied over the range of one order of magnitude, the variable potentiometer performing one full revolution through one range of magnitude of the time scale during the feed of the recording chart. After each revolution of the potentiometer, a change-over of the measuring range may be effected.

The invention is more fully explained by way of the embodiment disclosed by the accompanying drawings and the following detailed description.

In the drawings:

FIG. 1 is an illustration of a fractogram is obtained with prior art apparatus.

PEG. 2 shows in schematic form a device in accordance with the present invention.

FIG. 3 shows by way of example a diagram recorded with the device of this invention.

A synchronous motor (not represented in the drawings) is switched on when the substance of interest in injected into the carrier gas stream. A disk 1 fitted with a driving pin 2 is mounted on the shaft of the synchronous motor. After the shaft of the motor has performed one revolution, pin 2 contacts a dog 3 which is provided .on a disk Disk d is mounted on the driven shaft of the transmission 5. Disk 4 is thereby rotated and, consequently, shaft 5' is driven. The transmission 5 is so designed and constructed that with a constant driving speed, the speed of the driven shaft 5" is inversely proportional to the time which has elapsed since the start of the experiment and thus since the moment the motor was set in motion. The equations shown in transmission 5 indicate that when the angular velocity ((11 of disk 4 is constant, the angular velocity (m of disk 6 is inversely proportional to time.

A disk 6 carrying a driver pin 7 which is adjustable in holes 7 in accordance with a graduated scale 8 is mounted on the driven shaft 5".

After the driven shaft 5 and the disk 6 have performed a certain angular movement which can be adjusted on the graduated scale 8, pin 7 comes in contact with a dog 19 of a recording cylinder 9 and starts to set the latter in motion.

Numeral .11 designates a recording pen which is mounted on a slide 12. Slide 12 is movable axially with respect to the recording cylinder and may be moved in any known manner in accordance with an electric measured value.

This electric measured value U comes from a logarithmically wound variable potentiometer on which is impressed the measuring voltage U The measuring voltage U is supplied by a detector which is arranged at the exit of the column containing the separating substance and which supplies a measuring voltage as soon as the individual components of the mixture of interest appear. The detector may be a Wheatstone bridge of the aforementioned type, for instance, but any other suitable means may also be used for this purpose. The potentiometer 13 is coupled with the recording cylinder According to the invention, the number of revolutions of the recording cylinder satisfies the following equation:

where N designates the number of revolutions of the recording cylinder. Thus, after 1,000 revolutions of disk 1, disk 4, and shaft 5', recorder cylinder 9 will have completed exactly 1 /2 revolutions.

If now disk 1 has an angular velocity of 4 rev. w

the first half revolution of the driven shaft 5" is completed after an interval of time of 2.5 minutes; the second half revolution after 25 minutes, and the third half revolution after 250* minutes. The graduated scale 8 permits setting time 2 from 0.25 to 250' minutes. Even in the event of the last mentioned adjustment, a time in terval from 25 up to 250 minutes will still remain for the measurement.

The variable potentiometer 13 may be coupled with the recording cylinder 9 by means of a rope drive so that it performs a full revolution if the recording cylinder has turned one half revolution. The tapped voltage is thereby continuously varied proportional to the time by the factor 10. Thereupon, the additional change-over of the measuring range is effected, and with the following half revolution of the recording cylindercorresponding to a full revolution of the variable potentiometer-a continuous variation of the sensitivity up to a factor of takes place.

A diagram such as illustrated in FIG. 3 is then obtained. The bands of the individual substances, CH for example, are preliminarily marked on the recording tape. Graduated scales are printed at these points to permit reading the various heights of the bands which constitutes a means for directly determining the concentrations of the respective substances.

What is claimed is:

1. In a signal recording system including analyzer means for determining components of a sample, means for introducing a sample into said analyzer means, said analyzer means generating upon each introduction a train of time-displaced signal peaks providing a measure respectively of different components in said sample, and signal recording means, the improvement wherein said signal recording means comprises:

chart means having a time axis;

chart marking means movable transversely to the time axis of said chart means in response to each of said signal peaks;

driving means adapted to provide relative movement between said chart means and said chart marking means along the time axis at a variable speed inversely proportional to the time elapsing from the introduction of said sample; and

means for starting said driving means upon the appearance of a preselected signal peak.

2. The apparatus of claim 1 wherein said driving means comprises a constant speed motor means and a variable speed transmission means driven by said motor.

3. The apparatus of claim 2 wherein said transmission means is characterized by an output speed 100 which bears a relationship to the input speed wt defined by the equation:

4-. The apparatus of claim 2 wherein said means for starting comprises a clutch between said constant speed motor means and said chart means whereby said motor means rotates through a finite angle before said chart means is actuated thereby.

5. In a signal recording system including analyzer means for determining components of a sample, means for introducing a sample into said analyzer means, said analyzer means generating upon each introduction a train of signal peaks providing a measure respectively of different components in said sample, and signal recording means, the improvement wherein said signal recording means comprises movable chart means; driving means adapted to move said chart means at a continuously variable speed inversely proportional to the time elapsing from the introduction of said sample; means for starting said driving means upon the appearance of a preselected signal peak; electrical attenuator means adapted to receive said signal peaks and having a variable output; means for varying the output of said attenuator means; chart marking means movable transversely to the direction of movement of said chart means; and means for moving said chart marking means proportionally to the output of said attenuator means.

6. The apparatus of claim 5 wherein said attenuator means is a logarithmically wound potentiometer.

References Cited in the file of this patent UNITED STATES PATENTS 2,406,764 Guillemin Sept. 3, 1946 2,429,236 Potter Oct. 21, 1947 2,899,258 Spracklen Aug. 11, 1959 2,904,384 Norem Sept. 15, 1959

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