DE1648951C3 - Gas analysis measuring device - Google Patents

Description

The invention relates to measuring devices for the qualitative and quantitative analysis of gas mixtures or of mixtures of substances that are added before the measurement or immediately at the inlet of the measuring devices can be converted into the gaseous state.

Gas chromatographs are mostly used today as analytical measuring devices for the analysis of complicated gas mixtures used. A qualitative analysis is mainly carried out in gas chromatography by determining the relative exit times. However, this method has a number of disadvantages. The analyzer must first be calibrated for the "suspected" substance. In addition, is the evaluation is very complicated and often unreliable. Therefore detectors are suggested again and again and used that, connected to the outlet of the gas chromatograph, not only on the off respond to the substance escaping from the chromatographic separation column and after a preliminary calibration measure the amount of substance, but are also able to determine the substance being released.

Universal detectors, such as mass spectrometers and detection devices that work according to the density measuring principle, have been found to be the most suitable for this purpose.

If a substance is identified by its density (Martin's density meter), the display shows an am The detector connected to the outlet of the chromatographic column determines the density difference between the measuring gas mixture and carrier gas again (see, for example, M a r t i η A. J. P., James A. T., Biochem. J., 63,138, 1956).

ίο However, the density meters have the following disadvantages:

a) the determination of the molecular weight of the components requires knowledge of the quantitative Composition of the measuring gas mixture or entering a reference substance with known molecular weight in the mixture sample and the repeated inclusion of a Chromatograms with different carrier gases;

b) the accuracy of the molecular weight determination and the range of the molecular weights to be measured depends on the molecular weights of the components and the carrier gases;
c) there is an exact standardization of the test conditions

conditions (keeping the carrier gas velocity constant and the entered sample quantity) is required.

The density meters are still devices of relatively low sensitivity because their mode of operation is based on based on the principle of thermal conductivity. Such a density meter can be installed, for example, at the outlet Do not use capillary columns with low throughput.

The density meters enable the molecular weight to be determined on the basis of a density measurement. Other methods for determining molecular weight are also known, in particular the effusiometric method Proceedings. This is due to the fact that the outflow velocity of a Gas from a closed volume, an effusion chamber (it is also called a Knudsen cell) as Knudsen flow (i.e. under conditions where the free path of the molecules is greater than the diameter of the orifice) inversely proportional to the square root of the molecular weight is. From the pressure curve in the effusion chamber over time, measured by some method conclusions can be drawn regarding the molecular weight. However, an accurate molecular weight determination is possible according to the effusiometric Ver process only possible if there is only one or at most two substances are in the chamber, or if the measuring device used only refers to the component of interest.

The effusiometric process has also been combined with the spectrometric process (see, for example Friedel A. R., Charkey / ■. G., J. Chem. Phys., 17, 584, 1949).

On the other hand, the use of effusiometers in gas chromatography is already known, as can be seen from Bayer, Gaschromatographie, 2nd edition, Springer Verlag 1962, p. 181, and Dal Nogare, Juvet, Gas-Liquid Chromatography, Interscience Publ, 1962, p 236, based on a publication by Griffiths, James and Phillips in Anatyst, 77, 1952, p. 897.
The following measuring devices or -ver-

<t

drive to the analysis of gas mixtures with a chromatographic separation column and a referring the carrier gas insensitive detector, in particular a mass spectrometer, di; the identification of the substance in the chromatogram according to the mass spectrum.

1. Part of the gas flow emerging from the chromatograph is measured by a single-jet mass spectrometer, the remaining part by a chromatographic detector (ketharometer or a Ionization detector). The ratio of the signals from the mass spectrometer to the signals from the chromatographic detector identifies the substance in the chromatogram (see for example Henneb e r g D., Z. Anal. Chem., 183, 12, 1961). This analytical measuring device requires more frequent prior calibrations, since both the mass spectrometer and the chromatographic detectors do not have stable absolute sensitivity over a long period of time.

2. Part of that which emerges from the chromatograph The gas flow is uninterrupted by a high speed mass spectrometer, such as a transit time mass spectrometer or similar, promoted. At the moment a chromatogram is run through, the entire mass spectrum or a considerable part of it is registered quickly (see for example G ο h 1 k e R.S., Anal. Chem., 31, 535, 1959). This analysis facility requires complicated apparatus and, moreover, has relatively low sensitivity. The mass spectrometer is only used to identify the substance in the chromatogram, chromatographic measurements are usually used for quantitative measurement of the substance concentration Detectors or additional interceptors in the mass spectrometer against which the unsplit Ion flow from the ion source of the mass spectrometer is judged.

3. The entire gas stream emerging from the chromatograph is fed into a mass spectrometer two collectors, which are common to two for all substances in the mixture to be analyzed Mass lines or is set to two groups of mass lines. The relationship between the The intensities of these lines or groups of lines are used to identify the substance and to register it of the ion titrates from each of these lines or groups of lines by determining the areas under the recorded chromatograms for quantitative Determination of the substances (see, for example, the French patent specification 13 67 641, from T a 1 r ο s e, W. L., Tanzy re w, G. D., G ο rich k ο w, W. L, Greek, W. D., Kibalko, L. A.). This Analytical measuring device surpasses the simplicity and sensitivity described above, it suits you but with regard to the ability to identify substances, their mass spectra are only lower Accuracy are known, according to. A molecular weight determination without prior determination of the Substance is not possible with this analysis device. So

The mass spectrometer is in some ways an ideal chromatographic detector. At his However, it is desirable to use the mass spectrum of the "suspected" substance at least approximately to know, or at least to be sure, that the heaviest of the observed ions of the mass spectrum is an undissociated molecular ion. But there are many substances during ionization If a strong dissociation also occurs in the mass spectrometer, the determination of the undissociated is Molecular ions unreliable, so that the sensitivity the measuring device with which one must determine the undissociated molecular ion becomes low.

The invention is based on the object of specifying an analytical measuring device for gas mixtures, which allows the identification of the components of gaseous and liquid mixtures by a allows precise determination of their molecular weights.

This task is performed with a gas analysis measuring device with a chromatographic separation column and a vacuum detector that is insensitive to the carrier gas, in particular a mass spectrometer, solved according to the invention in that an effusion chamber for determination in the measuring device the mixture components according to their molecular weights is provided that the inlet opening the effusion chamber with the outlet opening of the chromatographic separation column via a valve is connected, which enables a separation of the chamber inlet that the effusion chamber at least has an outflow opening for the components of the measurement gas mixture, which communicates with the inlet opening of the vacuum detector is connected, and that the outflow openings of the effusion chamber so are dimensioned that the outflow of the measuring gas components through these openings when the Valve takes place as a Knudsen flow.

When operating the analytical measuring device in connection with more powerful packed chromatographic Separating columns, it is advantageous to have a flow branch between the separating column and valve to arrange an auxiliary valve and the latter to close and open simultaneously with the main valve.

When using packed chromatographic separation columns, the effusion chamber can also be advantageous have at least one further outflow opening for the components of the measurement gas mixture to which a vacuum pump is connected. The dimensions of this opening are also chosen so that the component flows out of the chamber as a Knudsen flow when the valve is closed.

The analytical measuring device according to the invention has the following advantages:

1. Both gaseous and liquid mixtures can be used through precise molecular weight determination of the components are analyzed, both qualitative and quantitative Result of the content of the individual components in the mixture to be analyzed can be won.

2. The measuring device enables identification of the measuring gas components both according to their molecular weights and according to others Parameters, for example in the chromatographic process according to the migration speeds the components through the chromatographic column.

3. There is no need to calibrate the measuring device more frequently with "pure" substances.

4. Ease of manufacture and operation.

The invention is illustrated below with the aid of a few exemplary embodiments with reference to FIG Drawings explained in more detail. It shows

F i g. 1 the diagram of a first embodiment of the analytical measuring device,

F i g. 3 the scheme of a second embodiment of the analytical measuring device,

F i g. 4 the scheme of a third embodiment of the analytical measuring device,

F i g. 5 shows a section of a chromatographic curve measured with the analytical measuring device in a schematic representation,

F i g. 6 shows a section of a chromatographic curve measured with the analytical measuring device with accelerated time sampling in the area of effusiometric analysis in a schematic representation,

F i g. 7 shows a section of a chromatographic and measured with the analytical measuring device effusiometric curve in a schematic representation,

F i g. 8 shows a section of a with the analysis measuring device when measuring according to the integral method obtained chromatographic curve in a schematic representation,

F i g. 9 shows a cross section through the effusion chamber, the valve and the mass spectrometer chamber with ion source,

F i g. 10 the ionization chamber on the analytical measuring device,

F i g. 11 a diagram to illustrate the with the measuring device according to the integral method results obtained in the molecular weight measurement,

F i g. 12 is a diagram to illustrate the measurement results obtained in the determination of the molecular weight were obtained with the analysis measuring device according to the differential method.

The Analysenmeßeinrichtung containing an effusion cell 1 (F i g. 1, 2), a vacuum detector 2, a chromatographic separation column 3, a valve 4 and a writing device 5. At the detector 2, a pump is connected, which conveys the gas to be measured in the direction of P.

A further exemplary embodiment for the measuring device is shown in FIG. 3 can be seen. This differs from the arrangement according to FIG. 1 through a branch 6 arranged between the chromatographic separation column 3 'and d: m valve 4, an additional auxiliary valve 7 and a chromatographic detector 8. A vacuum pump (with the conveying direction P) and a special writing implement 5' are connected to the detector.

The embodiment according to FIG. 4 differs from the two previous ones only in that the effusion chamber has at least one other outflow opening for measuring gas components connected to a vacuum pump (conveying direction P ') in addition to an opening for the outflow of the measuring gas components into the vacuum detector 2. This opening is dimensioned so that it flows out as a Knudsen flow.

The outflow through the additional opening is both when recording the chromatogram and of determining influence when registering the effusiometric curve.

One of the pumps (with the conveying direction P ' or P ") can be omitted from the arrangement if the other pump has sufficient efficiency (such an arrangement is shown in FIG. 4 with dashed lines).

The analytical measuring device works as follows:

The entire amount of gas flow emerging from the chromatographic separation column 3 is through the Chamber 1 and detector 2 passed. As long as the components to be separated are still in the separation column 3 are located, the valve 41 at the inlet of the chamber 1 is open. At the moment when the gas component reaches the chamber 1 and the detector 2, the valve 4 is closed suddenly, see above that part of the component in the chamber 1 remains pressed. After closing the valve 4, the

ίο component continues its movement from chamber 1 into detector 2 together with the carrier gas. This gas flow can only come about if the pressure in the detector 2 is always lower than the pressure in the chamber 1. The detector is thus evacuated and the concentration of the component N in the chamber 1 is reduced according to the exponential law

^N =

(D

In it is

N _{0 is} the concentration when the valve is closed,

t is the time from the time the valve closes,

T is the absolute temperature of the gas in the effusion chamber,

M is the molecular weight of the component,
V is the volume of the effusion chamber,

α is a constant (in the simplest case proportional to the diameter of the outflow opening of the effusion chamber).

The discharge of the carrier gas takes place according to the same law (but of course with a different value of M). The carrier gas flow does not make it difficult to determine the component, since the detector should be insensitive to the carrier gas, as required.
The flow conditions are selected so that a Knudsen flow is established at the outlet from the detector chamber 2. If the pressure in the chamber 1 is significantly greater than the pressure in the detector 2 and the pressure in the detector 2 is significantly greater than the pressure behind the detector, this can happen with Knudsenstrom

The detector output signal proportional to the partial pressure of the substance in the detector is also considered to be proportional can be viewed with the concentration of the component in chamber 1.

= abN (2)

Here, b denotes a factor that is dependent on the substance properties and the detector sensitivity, but remains the same at a constant volume velocity of the gas sucked out of the detector. After inserting (1) into (2), the following expression results for /

where I _{0 is} the signal amplitude at the moment the valve closes and α is a device constant.

7 8

The constant analysis of, for example, 10 components with one

_r _. Molecular weight of about 10 ² about 200 to 300 s in

_ V \ M | 4 | Claims. The duration of the chromatographic

a \ j T analysis of a complicated mixture is 10 ³ to

5 10 ⁴ p. Experience has shown that the resolution

is the outflow time constant for a substance with the chromatogram in the separation column 3 during

the molecular weight M. this time is negligibly small. (Also is

The molecular weight M is determined by solving it seldom necessary the molecular weights of all

Equation (3) is determined, with the time components being determined in a single experiment as the calibration value),

constant τ ₀ (outflow time constant at M = 1) applies. i ₀ The second cause of the reduction in resolving power can thus be regarded as suppressible

y will.

J / 7 ^ ■ '"*' I ^m upper part of the F i ₀ = g Ί. 5 is a section of

^a ". recorded with the analytical measuring device

15 chromatogram shown. Is on the abscissa axis

This time constant is determined by recording the time and, on the ordinate axis, the amplitude of the

Curve (3) for the chromatographic maximum detector output signal / plotted. There are two

of a substance with known molecular weight M are shown successive chromatograms. to

definitely. the times A, A ' , the valve 4 of the effusion

In the subsequent analysis of the curve of the ao chamber closed and at times B, B '

Equation (3) takes the logarithm and opens. There are three in all three embodiments

agree the size M from the tga, given the inclination of the possibilities of application.

Line In / = f {t). For the molecular weight ",,. " _Λ ""

the following formula then results: ^a ) ^{The Sl} 8 ^{nal for} closing and opening the

₂₅ shut-off valve is activated by the operator

. , _{Give N} 2;

M _ / _ J. (6) b) the closing signal is given by the operator

V n> tg α / given and the opening signal is automatic

of a timing relay after a preset

When function (3) has been taken up, the valve 4 between the separation column 3 and the released one opens 30 minutes after the valve has been closed; .....
Effusion chamber 1, and a stationary c) the closing _{signal W1} rd also arises automatically from the carrier gas flow. In the detector 2 is released, namely at the moment in which the not yet detected part of the chromatogram. Detector signal when recording a front or This part is registered by the recorder 5. In the trailing edge of the peak in a certain scale-like manner, all or only those of the value on the recorder 5 are reached,
operator selected subsequent chromatograms. The molecular weight is determined from the course of the

In the measuring device, special dimension curves were determined in sections AB, A ¹ B ' . The measures against a reduction in the resolution accuracy of the subsequent arithmetic capacity of the chromatograph are provided, the evaluation will be greater if two reasons could arise on section AB. Once the or A becomes 'B'

Resolving power through the finite content V _a) accelerates the temporal scanning,

the chamber 1 impaired. Therefore, the in- ^ _{ejn further} writing implement 9 (Fig. 2) with a higher

hold K selected so that chamber 1 only automatically adopts a low 45 recording speed.

Part of the chromatogram. switches and

On the other hand, the resolving power is DA _{c) a digita} i _it voltmeter with low inertia

due to the fact that the gas flow is switched on automatically after closing the.
Valve 4 is accumulated in the separation column 3 (is

the area in which the portion of the chromatogram recorded by the effusion chamber is not located, somewhat moderately taking into account the amount of the commercially available approach to the valve). The chromatographic writing instruments met,
In the case of a jammed flow, it is advisable to stop the graphic separation, of course, while the dissolution by tape transport on the sections AB and A ¹ B ' diffusion continues. So that the latter 55 on the device 5 recording the chromatogram does not have to stop and switch off the device during the total duration of all congestion. That becomes large after, the outflow time constant must be sufficient variant a) the recorded chromatogram is small. Since the reduction in the chamber volume V FIG. 6 and that obtained according to variants b), c) also leads to a reduction in T ₀ , these chromatograms in FIG. 7 (above). In Fig. 7 Both causes of a reduction in triggering are the same - 60 below is the recording of the activated second to be combated in good time. The time constant τ ₀ is, however, the writing instrument 9 and the sketch for the following downwardly limited by the time constant of the detector 2, evaluation of this recording (interference level limit amplifier and the recorder 5. A nation and logarithmizing),
Closer investigation shows that from this standpoint, a time constant τ ₀ S 0.3 to 0.5 s favorable 65 is increased when the signal is on the section. It is shown below that the effusiometric AB can be reduced to practically the interference level. Curve in the course of some time constants τ- For this purpose, the section AB must be at least equal to the increase. This means that the effusiometric time constant should be three times τ. As you can see is

the chromatogram according to variants b) and c) is clearer.

The presence of admixtures in the carrier gas to which the detector 2 responds in concentrations which are comparable with the concentration of the component to be analyzed can in principle make the effusiometric analysis somewhat more difficult. If the molecular weight of the admixture differs considerably from the molecular weight of the component, the curve In Z - / (/) has a kink, and the evaluation enables the molecular weight M to be determined.

The accuracy of the determination of the molecular weight of the components is greater when the carrier gas is contaminated, and the evaluation time is shorter if an integrator is provided in the amplification part of the measuring device. During the effusiometrischen analysis is the integrator output signal S after a period of /> 5 to 6 · τ with sufficient accuracy from the relationship In the presently described Analysenmeßeinrichtung is to integrate an RC chain and an existing full-feedback in the measuring device DC amplifier 10 (Fig. 2) is used. The input resistance of the amplifier serves as the λ-element of the chain, while the C-element is switched on between the control grid and the input resistance of the amplifier (the arrangement of the ßC-chain elements in the DC amplifier can be seen from FIG. 2).

In the circuit described above, the output signal of the amplifier has the form:

Λ.

JjL

S = Ιότ _ο βΤ + Ii'T ₀ ] / M] + Z ₁ ;

reproduced, where / ' _{0 is} the current value of the component signal at the start of integration, J ₀ "is the current value of any admixture with the molecular weight M in the carrier gas at the start of integration (this molecular weight must not be a multiple of the molecular weight of the component) and /, the current value the interference level or noise signal of the detector The latter also includes signals from any very heavy impurities in the carrier gas.

The integrator becomes after a specified, but constant for the respective test series Period of time switched on simultaneously with the closing of valve 4 or shortly thereafter. As in the equation (7), the integral becomes practically a linear function after some time constants τ have elapsed, so that the curve / = / (/) becomes a straight line. the graphical extrapolation of this straight line at the time of the start of integration gives the value

where τ is the outflow time constant of the addition of carrier gas is.

Analysis of this equation shows that the output signal of such an integrator is not an integral of the ion current for small values of /, but becomes one for sufficiently large t.
With ι > τ and /> r the expression of the form applies:

U =

The output signal U thus becomes a linear function of t. The extrapolation of this function at the time the integrator is switched on gives the value

U = Z ₁ R ₊ -L

Z- _Tl) .

(13)

= / ₀ 't ₀

/ o'r ₀ sc].

Since the concentration of the admixture in the carrier gas is usually fairly constant, the value Z ₀ 'r ₀ ylHTuT of each chromatogram can be determined by subtracting from ^ _ the value ^ ₀ "T ₀ ] / ~ M ~ measured between two chromatograms one can also _{measure the value Z 0} "between two chromatograms and _{obtain the value Z 0} by subtracting the values Z ₀ " and Z ₁ from the instantaneous _{value Z 0} at the time of each start of integration.

The size Z ₁ Z? is the potential difference IZ ₁ , which is caused by the noise current of the detector at the input resistance of the amplifier when the integrator is switched off.

The comparison of expressions (13) and (8) gives

UU ₁ =

C '

(14)

In the same way the difference

(U - U ₁ ) " = 2l

- Λ> ~ ΛΓ ~ Λ

The time constant T ₀ is determined from the peak of a substance (or from the peaks of several substances) with a known molecular weight M.

The molecular weight M of the unknown substance is determined using the following formula:

determine by integration in the pauses between the peaks or chromatograms. On the other hand OFL ^M? ™ ^entan «« rt of the voltage drop at the input of the amplifier ^ resistance at the moment of integration beginning

o = (Z ₁ + Z ₀ '+ Z ₀ ") R , (16)

** ^Β ™haben ^ evoked

= Z ₀ " R

(17)

11 12

is. The comparison of (14) to (17) and (10) separation columns are the second and third embodiments example better suited.

The operation in the second embodiment

w _ / f ^ £ \ ΓJ ^ ~ ^ i) ~ ^ _J ~ __m_'L ~ l ² (iHi does not in principle differ significantly from the

~~ \ ^r o / L U _n ~ U ₀ "-LJ ₁ J ⁵ in the first embodiment.

However, the main part of the gas flow emerging from the filling column 3 '(FIG. 3) arrives in the opposite direction

The quantity (C / r ₍₁ ) ^! ) Does not play the role of a chamber 1 in the determination of the effusion molecular weight by integration in the first exemplary embodiment, but is either drained or a calibration constant. A conventional chromatographic detector recorded according to this method 8 The chromatogram is given in Fig. 8 (above), which in this case shows the quantitative result. The abscissa axis is the time axis. The values are supplied. In this embodiment, the detector output signal U are on the ordi transition Both venous axes are plotted for effusiometric analysis, showing two on-tile 4 and 7 closed at the same time.
other peaks. In the time points Q and A '15 The operation of the third embodiment of the valve 4 of the effusion cell 1 is closed corresponds in principle equal to that of the first execution and the integrator turned on. The shutdown of the example.

Integrator takes place at times C, C and the F i g. 2 gives the structure of the analytical measurement

opening of valve 4 at times B, B '. direction in details again schematically.

Chromalograms of the kind given are only shown. The structure of the effusiometer chamber 1, the venus the condition that the outflow time tils 4 and the mass spectrometer chamber with the ion constant of the component under investigation is greater, however, the source is shown in FIG. 9 shown in more detail (the than the time constant of the /? C integrator and that the effusion chamber 1 and the valve 4 are constructive Concentration of the examined component higher combined into one assembly).

is than that of admixture. This condition is assumed to be the same. The description below is intended to be the same Equation (11). refer to these two drawings in good time.

If the above condition is observed. The gas flow emerging from the chromatographic separation column 3 on the chromatographic curve at the time passes through the valve 4 and the point of the integration start a clearly recognizable chamber 1 into an ion source 11 (FIG. 2) and becomes Knick, which significantly facilitates the precise determination of U ₀ 3 ° from this by an evacuation system. from a diffusion pump 12 with cold trap and

A backing pump 13 with connecting lines can be used as a universal detector in the described Use an analytical measuring device: exists. The pressure in the chamber of the mass spectrometer

a) A mass spectrometer that is always on a meter and the fore-vacuum pressure are using certain mass peak value or on a 35 of a combined heat conduction and ionization group of peak values for which no peak value vacuum gauge 14 was measured.

heard of the carrier gas. The gas throughput is regulated with valve 4

^{b) A device that takes up the whole and amounts to 0.2 to 0.3 cm 3} / min in the case of capillary separation columns (under normal mass spectrum of the experimental ratios from the effusion chamber).
The valve 4 consists of a housing 15 (FIG. 9), which enables the operator (in the case of particularly perfect embodiments of the analysis device that simultaneously act as the housing of the effusion chamber 1). It is important to emphasize a valve seat 16 and a valve needle 17 that when using such The latter also forms the core of the outside measuring devices a mass spectrum much more precisely attached electromagnet 18 the position of the core in relation to the trometers with rapid registration of the mass - other parts of the magnetic circuit precisely determined. The spectrum can be evaluated because the law of throughput is precisely known when the magnet 18 is excited, the pressure drop in the ion source of the mass by adjusting the magnet including the valve needle 17 spectrometer on the section AB compared to the valve seat 16 with the help of a micro and you can make an exact correction 5 ° meter screw 19 set. When switched off

Magnet 18 comes the needle under the action

j ^ _ Js-,. ". a spring 20 on the valve seat 16 to rest and

¹ 'closes the passage opening of the valve 4.

The majority of the ion source 11

of all mass peak values. In the 55 resulting ions (these are the ions with a

Formula (19) means t _{n is} the registration time of the «th mass value of over 12 mass units

measured peak mass value (from the first mass ion with the exception of the carrier gas ions from the collector 21

peak value calculated). (Fig. 2) collected. Experience has shown that

c) If the influence of the detector noise is often less, a particularly cheap and simple way of guiding the analysis measuring device can be a mass spectrometer, if the collector only collects ions with a mass value of more than 30 mass units, Ion capture always the largest part of the ions c'er noise current of the ions of H ₈ O, air and CO eli mixture components, but no ions of the carrier is minimized. Hydrogen gases are used as the carrier gas. or helium supplied from bottle 22.

The vacuum detectors are only able to 65 The ion current is proportional by means of a direct current to allow small mass flows of gases through amplifier 10 and an automatic potentiometer, as they almost only occur in capillary columns with slower recording speeds. Measured for operation on more powerful packed speed (approx. 5 to 20 mm / min).

13 ö - 14

During the time in which a chromatogram operates a cam disk 32 contacts 39. Dabe

Effusion chamber 1 and the detector 2 passes, a relay 42 responds and opens contacts 43, ie

if the electromagnet 18 of the valve 4 is switched off, the capacitance C of the direct current integrating chain

the valve needle comes into the closed position and the amplifier bridges. The output of blocks the passage of the gas. the chromato- 5 detector 2 arrives at the ÄC integrating chain. / is in

graphic column 3 into the effusion chamber 1. Amplifier 10 amplified and the chromatogram

The part of the writer 5 remaining in the chamber 1 begins to write an integral curve

Substance from the chromatogram flows over a The integration time is determined by the selected professional

or several openings in the membrane 23 (FIG. 9) of the cam disk 32 are determined. After finishing

in the detector 2 which integrates the outflow velocity io open the contacts 39, and there;

of the substance from chamber 1 (the volume relay 42 drops out. This also opens the contacts «

the chamber 1 and the dimensions of the openings 43 and the writer 5 registers the noise of the

are determined by the selected time constant τ ₀ ). Detector 2. After 2 to 3 s (this line

The valve 4 is operated manually by actuating the is in turn through the profile of the cam disk 2 "

Button 24 (Fig. 2) or determined automatically with the help of 15) the valve 4 opens and the recorder ί

Contacts 26 of a control device 25 actuated, which takes the registration of the chromatogram again

in a certain, the selected signal amplitude. The cam 31 and the contacts 38

arranged at a corresponding height and used to reset the motor contact relay 25

Pen pen to be closed. in the starting position.

The control device 25 consists of a set 20 The measurement of the admixtures in the carrier gas

of cam disks 27 to 32, which are triggered by a syn- dependent signal that is used to determine the molecular

chronotor 33 can be set in rotation and the weight according to equation (18) is required,

the contacts 34 to 39 after a preselected is made by the operator in the pauses between

Close the schedule. The structure of the control device shows the chromatograms by pressing the button

gives the operator the opportunity to run the measuring 25 24,

installation either in automatic or non-automatic. ,.

to operate automatically. The ^b > N.chtautomat.sche Arbe.tswe.se.

The desired operating mode is activated with the operating mode switch 40 of the control device 25

switch 40 set. is in position II. During the transit

a) The automatic mode of operation corresponds to the ³ ° & ⁿ f? ^d ™ , ^ "ΤΤ ^ n"? * "* ^Kam ™ ^rl position I of the operating mode ^{switch . Here, ™? D} , ^de " ^D * _{tekt c} ^{or 2 switch} ? ^{the Β ξ} * ^ι ™ ^ψψ ™ ^{α to} the automatic measurement of the molecular weights of the Motor33 Steuere.nr.chtung 25 by Betat.gung all in the mixture of existing substances. ^of £ ^no . ^pfes _Q ² ? ^{c 'n} * ^ further runs of the measuring process

b) The non-automatic mode of operation corresponds ^{to the} switch position I ab.

position II of the operating mode ^{switch 40. Here 35} measurement of the molecular weight according to the

the molecular weight is measured using a rential method.

one or more of the operator moves the selector switch 4J to position IV.

selected substances of the mixture. The measuring. . , ..,. , ..

direction is then set by pressing button ^a > Automat.sche Arbe.tswe.se.

24 during the passage of the selected ⁴ °. The operating mode switch 40 of the control device 25

The chromatogram through the effusion chamber ί is in position I.

and the detector 2 is activated. ,., ..,,, ^, j w

° ° During the passage of the maximum of the

In both modes of operation of the measuring device, chromatograms can be carried out through chamber 1 and the

the measurement after the differential as well as 45 detector 2, the recorder spring closes the contacts 26,

take place according to the integral method. The selected one whereby the motor 33 of the control device 25 in

The measuring method is set with switch 41. Movement is set. The cam disk 27 loads

The following is the sequence in which the switching operation is effected by actuating the contacts 34 and closing

indicated by the operator and the valve 4 and thus an interruption of the gas

the control device 25 when measuring the molecular 5 ° current from the chromatographic separation column 3 in

weight to be executed. the effusion chamber 1. The cam disk 30 opens

Measurement of the molecular weight according to the integral- the contacts 37, the writer 5 with smaller

method: tape speed from DC amplifier 10

The switch 41 is located m the position III. disconnected and the input of the latter short-circuited

a) Automatic ^{mode of operation: 55 becomes} · ^ / ΤΤ ^ ΐ ^ ™ "u ^ ^{di <} \ ^{contacts 36} 'τ-. rt-u * i. u An ucj -U- j causing the recorder 9 to operate at high tape speed 40 is in the _ability with its input to the amplifier 10. Now the cam 28 actuates the contacts 35 during the passage of the chromatogram and thus puts the motor of the recorder 5 through the effusion chamber 1 and the detector 2 60 out of operation and switches the motor, the pen spring closes the contacts 26, with that of the pen 9. The time for recording the motor 33 of the control device 25 is switched on the shut-off of the valve 4 and thus the profile of the cam disks are determined by the contacts 34. After an interruption in the gas flow from the chromatography of the molecular weight measurement, di e graphic separating column 3 into the effusion chamber 1. Contacts 34, 35, 36, 37 and 39 are brought back to their starting position by the respective cam disks or a predetermined time span according to the selected cam disk profile!). The valve opens 4. and the

of the device 5 resumes the chromatogram recording. The cam disk 31 with contacts 38 serves to reset the control device 25 to the initial state.

5 b) Non-automatic mode of operation.

The operating mode switch 40 of the control device is in position II.

IO

During the passage of the maximum of the chromatogram through chamber 1 and the Detector 2, the motor 33 of the control device 25 is switched on by actuating the button 24. The measuring process then proceeds in the same way as with position I of the operating mode switch 40 away. In the case of small concentrations, the proportion of noise in the integral value becomes relatively large. This makes it difficult the measurement. The detector noise can be compensated for by an ao shown in FIG Ionization chamber 44 can be achieved, which contains a radioactive emitter and is in the saturation state is operated.

The ionization chamber 44 of the type of a parallel plate chamber has two cylindrical electrodes 45, 46. The radiation from a radioactive source 47 (a / 3 radiation source from Promethium - 147 from 20 millicuries activity) enters the ionization chamber 44 through a closed with a grid Opening in the electrode 45. The electrode 46 forms the collector for electrons and negative ions. On the electrode 45 receives a negative potential from a power supply unit (in the Drawing not shown) with 400 V output voltage. The one flowing through the chamber 44 Current is determined by the dose rate in the space between the electrodes 45 and 46 and can through Adjustment of the radiation source 47 along the opening in the electrode 45 with the micrometer screw 49 in can be varied over a wide range. The ionization chamber is filled with dry air (or with any other gas) filled at atmospheric pressure.

The necessary compensation of the noise current of the detector 2 by the current of the ionization chamber 44 is set by the operator in the pauses between the chromatograms. He sets the switch 50 ( FIG. 2) to the position V _1, whereby the valve 4 closes, and then switches the measuring device to integrating by closing the switch 51. The ionization chamber 44 is disconnected with the switch 52 and the current of the ionization chamber 44 is set with the handle 53 to a value which compensates for the increase in the integral caused by the second term on the right in equation (11), that is, the inclined linear section of the Integral curve in a horizontal position, as shown in FIG. 8 shows transferred. The switches 50, 51 are then returned to the starting position.

The qualitative analysis can be performed using one of the following three methods

a) when recording the chromatogram without the effusiometric determination of the molecular weight of components - by measuring the area of the recording,

b) when recording the chromatogram without effusiometric Determination of the molecular weights of the components - by integrating the peaks

in the integrator (the switch 51 remains closed in this case during the measurement),
c) when recording the chromatogram with simultaneous effusiometric determination of the molecular weight - from a chromatogram that is recorded simultaneously with another detector or repeatedly but without using the effusion chamber 1, or by measuring the area of the peak "incised" during the effusiometric analysis (Fig. 5 , 8, above). The following graphical evaluation is necessary for this (FIG. 5 below and FIG. 8 below). A straight line is drawn through point c in such a way that it forms the extension of the left flank of the curve. The right edge of the curve is shifted along the time axis until point d meets the straight line (this position is shown with a dashed line). Then the horizontally hatched area under the curve is measured.

In this evaluation, the loss of substance is automatically recorded that arises during the effusiometric analysis. The relevant correction corresponds to the obliquely hatched area (FIG. 5, 8). The procedure described above remains self-evident only an approximation and does not take into account the complicated transition processes that occur on Play the entrance of the effusion chamber 1 when the valve 4 is closed and opened. Experience shows but that the error in a quantitative analysis of mixtures by this method is at most 2 to 3%. So it is at all within the error limits, as it is when evaluating not "Cut" curves occur.

The flow condition at the outlet of the chamber 1 during the effusiometric determination of the molecular weight depends on the chamber dimensions and chamber pressures. The pressure in the chamber at the moment the valve is closed is mainly determined by the flow conditions in the chromatographic separation column 3. With very large ones. Throughputs of carrier gas it can happen that the chamber pressure rises some time after closing the valve above the value which is necessary for the development of a Knudsen flow from the effusion chamber. Under these circumstances, the initial section of the experimentally determined curve, which corresponds to a certain time interval after valve closing, can show a deviation from the theoretical curve that results from the discharge law for the relevant molecular weight (the length of this section depends on the molecular weight of the carrier gas and is light gases some T ₀ ). The deviation from the discharge law is due in this case to the flushing of the measuring component from the effusion chamber by the carrier gas and to secondary phenomena in the ion source of the mass spectrometer, which occur at relatively high pressures in the chamber and ion source. Therefore, when determining the molecular weight according to the differential _{method, an initial segment of the length of a few T 0} on the time scale has to be disregarded when evaluating the effusiometric curve. When determining the molecular weight by the integral method, it is emp ^r chlenswert not, but later turn on the integrator at the time of valve closing bit (with a time delay of several T _0). the

^Ir 18

The required delay can be achieved by appropriately designing the cam disk 22 of the control device 25 can be specified.

In experiments with the analytical measuring device, a copper capillary separation column 50 m in length was used. A stationary phase serves as the filling. The column was arranged in a thermostat which ensured that a temperature in the range from 0 to 200 ^° C. was kept constant.

During the measurement, the temperature of the effusion ^{chamber was either kept constant between 100 and 150 °} C. with an accuracy of 0.3 ^° C. or the chamber temperature was measured regularly and used to correct the molecular weight according to formula (5). The vacuum system of the measuring device was maintained at a temperature of 200 ⁰ C, so that the analysis of substances of low vapor pressure was possible. A permanent magnet 54 (FIG. 2) ensured adequate stability of the mass spectrometer display. An ion source 11 of the type of the Nier's source was used in the mass spectrometer. The cathode was supplied with heating current by an electronic emission control device 55. This device also applies the required potentials to the electrodes.

The measuring device was tried out in the chromatographic analysis of some mixtures, whereby the molecular weights of components were to be measured, the substances from different Classes with molecular weights between 29 and 371 represented. The measurement results are in FIG. 11

ίο (measurement according to the integral method) and 12 (measurement according to the differential method). On the abscissa axis are the real ones and on the ordinate axis calculated according to formula (10) (with integral method) or (6) (differential method) Test values plotted for the molecular weights. The difference between measured and real Values was 2 to 3%.

The error limits of the analytical measuring device in determining the molecular weight of the gas

ao mixture components also determined by calculation.

With a registration with recorders and reasonable analysis times, the arithmetical value for the relative measurement error 0.1 to 0.5%.

In addition 5 sheets of drawings

Claims (3)

Patent claims: 1. Analysis measuring device for gas mixtures with a chromatographic separation column and a vacuum detector that is insensitive to the carrier gas, in particular a mass spectrometer, d adurchgekisiert that an effusion chamber (1) for determining the Components in the measuring gas mixture according to molecular weights is provided that the inlet opening the effusion chamber (I) with the outlet opening of the chromatographic separation column (3) The effusion chamber is connected via a valve (4) provided to shut off the chamber inlet (1) at least one outflow opening connected to the inlet opening of the vacuum detector (2) for the measuring gas components and that the outflow openings are dimensioned so that the outflow of the measuring gas components through these openings when the valve (4) is closed takes place as Knudsenstrom. 2. Analysis measuring device according to claim 1, characterized in that when using packed chromatographic separation columns (3 ') between the separation column (3') and valve (4) a flow branch (6) is arranged with an auxiliary valve (7) and that the auxiliary valve (7) with the main valve (4) is operatively connected for simultaneous opening and closing. 3. Analysis measuring device according to claim 1, characterized in that when using packed chromatographic separation columns (3 ') the effusion chamber (1) at least one more Has an outflow opening for the measuring gas components to which a vacuum pump is connected is and which is also dimensioned so that the outflow when the valve is closed as a Knudsen flow he follows.