FR2881227A1 - Mass spectrometer calibrating method for motor vehicle, involves establishing linear relation of constants or gradients to create curves of ratios of masses of sulfur dioxide and oxygen ions in function of sulfur dioxide concentration - Google Patents

Abstract

The method involves measuring ratios, between masses of ions of sulfur dioxide and oxygen, on respective gas check samples to obtain constants or gradients. A linear relation representing the evolution of constants or gradients with respect to oxygen rates is established to establish calibrating curves providing the evolution of dimensionless ratios of the masses in function of sulfur dioxide concentration, for a given oxygen rate. Independent claims are also included for the following: (A) a method for evaluating oil consumption of an engine by tracing sulfur dioxide using a mass spectrometer (B) a device for calibrating a mass spectrometer.

Description

METHOD FOR CALIBRATING A MASS SPECTROMETER, DEVICE FOR IMPLEMENTING IT

  IN THE EVENT OF AND APPLICATION TO THE TRACING OF SULFUR DIOXIDE IN THE EVALUATION OF THE OIL CONSUMPTION OF A

ENGINE.

  The present invention relates to a method of calibrating a mass spectrometer, and a mass spectrometry device for carrying out the method, as well as to the application of the method and the device to the tracing of sulfur dioxide in the evaluation of the oil consumption of an engine.

  Mass spectrometry has applications in the most varied fields, such as gas analysis, structural analysis of organic compounds, qualitative and quantitative analysis of mixtures, or analysis of the degree of abundance. isotopes or the analysis of impurities, concentration profiles, etc. A mass spectrometer is a physico-chemical analysis device, which allows the study of ions or charged molecules formed from a sample in appropriate conditions.

  A mass spectrometer consists of four essential elements: - a sample collection and transport system from the sample to the ion source; an ion source that produces ions from the source to be analyzed, accelerates them and forms a beam; an analyzer which, by means of various combinations of electric and magnetic fields, separates the ionic species into distinct beams which it filters, according to the ratio m / e of their mass m to their charge e; - a detector that highlights the presence of ions and informs about their abundance.

  In general, the sample (molecules, atoms) in gaseous form is introduced into the ion source or ionization chamber. The gases in the sample are ionized by electron impact. The atoms are thus electrically charged with positive or negative ions, namely cations or anions, which, unlike the electrically neutral particles, can be set in motion by an electric field and deflected by a magnetic field.

  The ions are accelerated by a potential difference created by an electric field. Their speed depends on the mass, the load and the voltage.

  The ions enter the analyzer occupied by a magnetic field in order to be separated. Their trajectory is deflected under the action of the force due to the magnetic field. They describe a circular trajectory whose radius depends on the mass of the ion, and strike at the end of the trajectory a photographic film on which they leave a trace.

  Calibration is a fundamental step prior to any experimental measurement. It is a matter of determining the relation between the indications of the mass spectrometer and the values of the quantity to be measured, by comparison with a standard, which is a gas sample whose values to be measured are perfectly known. The calibration makes it possible to take into account in the measurement the test conditions (ambient temperature, hygrometry, etc.). The standard gas, the concentration of which is well known, is called SPAN.

  In general, known per se from the prior art, such a calibration requires a complete set of manipulations and many measurements. Dilutions of N2, SO2 and O2 from standard bottles are carried out in order to see what is the respective evolution of the number of strokes per second of SO2 and O2 measured by the mass spectrometer as a function of the concentration in O2. vary the gas flow rates of three standard bottles (SO2, 02, N2) while maintaining a constant total flow rate. The flow rate of 02 is constant to work at iso concentration of 02. The mass spectrometer then measures the number of strokes per second of S02 and 02. We establish a first series of curves of the number of strokes per second of SO 2 as a function of the concentration, measured in ppm (ppm, in the present text refers to the proportion unit-per-million units) of SO 2, each curve being set for a given concentration of O 2. A second series of curves of the number of strokes per second of O 2 is established as a function of the concentration, measured in ppm, of SO 2, each curve being established for a given concentration of O 2.

  On the one hand, such a procedure performed at the beginning of each new measurement or experiment is of a relative complexity, and considerably increases the duration of the calibration protocol.

  On the other hand, the two series of curves obtained do not have a parallelism, which would facilitate the extrapolation, and thus the calibration.

  But above all, it appears that in mixtures composed of sulfur dioxide (SO2) diluted with oxygen levels (02) more or less important the response of the spectrometer evolves according to the level of oxygen present.

  Similarly, it appears that the response of 02 is strongly dependent on the presence of SO2.

  This is an S02 / O2 interaction phenomenon.

  This phenomenon is attributed to a charge exchange reaction between SO2 and O2 within the analyzer of the form: SO2 + + 02 SO2 + 02+ SO2 + 02+ -i SO2 + + 02 We have: [SO2 + For example, when measuring oil consumption in automobile mechanics, any measurement of SO2 (fuel consumption depollution, ...) by mass spectrometry in the presence of 02 will face this difficulty.

  The aim of the present invention is to implement a new calibration method of a mass spectrometer which, on the one hand, takes into account and resolves this difficulty of measurement and interpretation due to the interaction between S02 and 02 at the level of the detection system, and, secondly, does not require, at each beginning of new experience, to achieve all of the previously mentioned curves beams. Therefore, it is a question of providing a new calibration method which makes it possible to draw the relation linking the concentration of SO2 and the rate of 02, in order to limit the complexity and especially the duration of the calibration protocol .

  More precisely, the object of the present invention is to provide a safe method which makes it possible to estimate the concentration of SO2 whatever the oxygen content present and then to carry out the correction necessary for the measurement of SO 2 to take into account the influence of O2.

  To achieve this goal, the method according to the present invention comprises the following steps: - is carried out, on a first gas standard sample, a first measurement by said mass spectrometer of the dimensionless ratio between the sulfur dioxide ion masses and oxygen per unit of time, which makes it possible to obtain a first constant or slope (P1) of the linear relationship between said ratio and the concentration of sulfur dioxide, for a known oxygen level in said first standard sample, a second measurement by said mass spectrometer of the adimensional ratio between the masses of sulfur dioxide and oxygen ions per unit is carried out on a second standard sample of gas having an oxygen content different from said first standard sample; of time, which makes it possible to obtain a second constant or slope (P2) of the linear relationship between said ratio and the concentration of sulfur dioxide, it is established, accordingly, the linear relation representative of the evolution of said constant or slope with respect to the oxygen level, which makes it possible to establish, without additional measurement, the set of calibration curves each giving the evolution of the dimensionless ratio of the masses of ions of sulfur dioxide and oxygen per unit of time in order to determine the concentration of sulfur dioxide for a given oxygen level.

  Alternatively, the method may comprise, in addition, one or more measurement (s) additional (s) by said standard gas sample gas spectrometer (s) having an oxygen level different from the oxygen levels of said first and second measurements, said (or more) additional measurement (s) measuring the dimensionless ratio between the sulfur dioxide and oxygen ion masses per unit of time, which makes it possible to obtain one (or more) several other constant (s) or slope (s) of the linear relationship between said ratio and the concentration of sulfur dioxide.

  The invention is particularly applicable to the evaluation of the oil consumption of a motor by tracing sulfur dioxide, by means of a mass spectrometer. In this application, the process comprises the following steps: - the mass spectrometer is calibrated according to the method expressed above, so as to obtain the straight line beam giving the evolution of the dimensionless ratio between the mass of ions per unit of sulfur dioxide time and mass of ions per unit of oxygen time as a function of the number of sulfur dioxide concentration for a given oxygen level, - mass spectrometry is used to measure the number of strokes. Sulfur dioxide / second, the number of counts / seconds of oxygen is also measured by mass spectrometry, the ratio of the number of strokes per second of sulfur dioxide to the number of strokes per second is determined. of oxygen, the oxygen level is measured by means of an oxygen probe, the right line is determined among the said right bundle, as a function of the measured oxygen level, the concentration of sulphur dioxide.

  The invention also relates to a device for implementing the method according to the invention, which comprises: - a mass spectrometer, - an oxygen probe at the input of the mass spectrometer in order to measure the O 2 level.

  at least one flow meter at the level of the conditioning line, so as to control the quantities of standard sample gas injected into the mass spectrometer.

  Preferably, said flow meter is positioned at the input of the mass spectrometer.

  More preferably, when used for the tracing of sulfur dioxide on an evaluation bench of the oil consumption of an engine, said flow meter is positioned upstream of the furnace used in the oxidation of sulfur, Since this solution has the advantage of saving a flow meter, it also serves for the injection of oxygen for the oxidation of sulfur and HC. The invention will be better understood with the following description of examples. non-limiting embodiment of the object of the invention, accompanied by the drawings in which: Lai FIG. 1 is a beam of curves representing the evolution of the adimensional ratio between the number of strokes per second (mass of the ions in: the unit time) of the sulfur dioxide and the number of counts per second of the oxygen, depending on the concentration of sulfur dioxide, each curve being representative of an oxygen level.

  FIG. 2 is a graph of the curve representative of the evolution of the slope or coefficient governing the straight lines of FIG. 1 as a function of the oxygen level.

  FIG. 3 is the graph of FIG. 1, in which are shown the two calibration points designated 1 and 2.

  FIG. 4 is a graph representing the beam of straight lines which give, each for a given oxygen level, the evolution of the dimensionless ratio [counts per second S02 / counts per second 02] as a function of the concentration of SO2.

  The Applicant has succeeded in establishing the result according to which the evolution of the dimensionless ratio [counts per second S02 / counts per second 02] as a function of the number of ppm of SO2 for a given concentration of O2 is governed by a linear relationship, that is that is, the equation of a straight line.

  All of these evolutions (as a function of the O 2 content) describe, consequently, a straight line, as shown in the drawing 25 of FIG.

  In the drawing of Figure 1, are shown, as an example of implementation of the method, the lines which correspond to five different values of the oxygen level.

  For each oxygen level, the Applicant obtained the following values of the directing coefficient of the straight line (or constant of the linear relation represented by the straight line): Straight Rate Equation of the straight line 0% dl Y = 0.19498 X% d2 Y = 269, 71068 X% d3 Y = 515, 377753 X% d4 Y = 741.87827 X% d5 Y = 947, 96266 XY being the ordinate in ppm of sulfur dioxide, X being the dimensionless abscissa the ratio of the number of strokes per second of sulfur dioxide to the number of counts per second of oxygen measured by the spectrometer.

  It is noted that the steering coefficient can be considered as proportional to the level of oxygen present.

  The lines pass necessarily by the crossing point 0 of the abscissa and ordinate axes.

  By plotting the directing coefficient of each of these lines as a function of the O2 rate, we arrive at an almost linear relationship.

  Only four measurements make it possible to correctly evaluate the equation of this straight line, represented in the drawing of FIG. 2, and referenced D. In the present example of implementation of the method according to the invention, the Applicant has established that the points four measures were linked by a curve equation close to a straight line.

  This straight line passes by O. It answers, in the present example, to the following equation: Y = 0.00420 X, in which X is the Oxygen level, expressed in%, and Y is the slope, as indicated previously.

  The table below gives the coordinates of the four measurement points, from which the straight line D is drawn. On the abscissa the concentrations of O2 are represented, and on the ordinate the slopes or coefficients.

  Proportion 02 (%) Slope 0.023 0.044 0.063 0.081 It is also noted that the correlation coefficient is 1 when a third order polynomial interpolation is carried out.

  The calibration procedure is therefore based on the determination of some points taken at the extremes (highest SO2 concentrations). In the minimum case, a single point is sufficient.

  An example embodiment of a sampling method according to the invention will now be described, by way of non-limiting example of its object, in order to explain the simplicity and speed with respect to the calibration protocol of the invention. prior art.

  The points to be measured are, for example, the following two points, designated 1 and 2: Measure of point 1: Starting sample: SPAN SO2 / 02 dilution comprising 20% O2 and 20 ppm SO2.

  We measure the number of strokes / second of SO2 and 02. We can then position the point 1 on the graph of Figure 1, which shows the drawing of Figure 3. It is a line through the l origin O. The line D1 is therefore defined. The slope P1 of this line D1 can be calculated. It is then possible to position on the graph of FIG. 2 the point referenced A, of ordinate P1 on the ordinate axis representing the slope, and of abscissa 20 on the abscissa axis in% of O2.

  Measurement of point 2: Starting sample: SPAN SO2 / 02 dilution comprising 5% O2 and 20 ppm SO2.

  The number of strokes / second of SO2 and of 02 is measured. Point 2 can then be positioned on the graph of FIG. 1, as is also shown in the drawing of FIG. point 1, a line passing through the origin O. The line D2 is defined. It is then possible to position on the graph of FIG. 2 the point referenced B, of ordinate P2 on the ordinate axis representing the slope, and of abscissa 5 on the abscissa axis in% of O2.

  Two points are sufficient to draw the line D of FIG. 2. However, it is possible to measure for several points beyond two. The knowledge of this straight line D makes it possible to go back to the curve beam shown in the drawing of FIG. 4, which gives the evolution of the adimensional ratio [counts per second S02 / counts per second 02] as a function of the number of ppm from SO2 to iso [021. Indeed, for each rate of 02, we can read in Figure 2 a steering coefficient or slope of the corresponding line of Figure 4.

  On the graph of FIG. 4, 10 straight lines, each corresponding to a value of the oxygen content, are represented from 1% to 10% of O 2.

  With a 300 ppm standard bottle, this process is valid for the ppm levels presented (between 0 and 20 ppm).

  One of the advantages of this method is to be able to calibrate a SO2 measurement of a few ppm.

  As indicated above, the method thus described finds a particular application given here by way of non-limiting example of the object and applications of the present invention. The measurement of SO2 is considered during an oil consumption measurement of a motor vehicle engine. In the engine testing phase, the following is carried out as follows: the number of strokes per second of SO.sub.2 is measured by mass spectrometry, the number of strokes per second of 02 is also measured by mass spectrometry, the ratio between the number of strokes per second S02 and the number of strokes per second 02 is determined, the oxygen level is measured by means of an oxygen probe, the right line is determined among the line of strokes. Figure 4, each line corresponding to a given oxygen level (expressed in%), - we can then evaluate the concentration of SO2 in ppm of SO2.

  The present invention also relates to a mass spectrometry device, which comprises: - a mass spectrometer, - an oxygen probe at the input of the mass spectrometer in order to measure the O 2 level.

  at least one flow meter at the level of the conditioning line, this (or these) flow meter (s) makes it possible to control the quantities of standard SPAN gas injected into the mass spectrometer. They can be positioned anywhere in the packaging line but preferably: - either directly at the input of the mass spectrometer or upstream of the furnace, this solution having the advantage of saving a flow meter, it also serves with the injection of O2 for the oxidation of sulfur and HC.

  The method according to the present invention allows calibration of the mass spectrometer to perform a sulfur dioxide measurement by taking into account the problem of mutual dependence of SO2 and O2 concentrations from a reduced number of measurement points.

  Several measurement campaigns based on dilutions of standard bottles SO2 / 02 / N2 made it possible to show the results obtained.

  The numerical example of the measurements is given by way of illustration of the process, which is defined by the appended claims.

Claims (6)

  1. Method for calibrating a mass spectrometer, used in particular for measuring the concentration of sulfur dioxide in a gaseous mixture subjected to the influence of the presence of oxygen in its constituent elements, characterized in that it comprises the following steps: - a first measurement by said mass spectrometer of the ratio between the masses of sulfur dioxide and oxygen ions per unit of time is carried out on a first gas standard sample, which allows to obtain a first constant or slope (P1) of the linear relationship between said ratio and the concentration of sulfur dioxide, for a known oxygen level in said first standard sample, is carried out, on a second sample gas standard having a different oxygen level of said first standard sample, a second measurement by said mass spectrometer of the ratio of the sulfur dioxide and oxygen ion masses per unit of time, which allows to obtain a second constant or slope (P2) of the linear relationship between said ratio and: the concentration of sulfur dioxide, - the linear relationship representative of the evolution of said constant or slope with respect to at the oxygen rate, which makes it possible to establish, without additional measurement, the set of calibration curves each giving the evolution of the dimensionless ratio of the masses of sulfur dioxide and oxygen ions per unit of time as a function of the concentration of sulfur dioxide for a given oxygen level.   2. Method according to claim 1, characterized in that it comprises, in addition, one or more measurement (s) additional (s) by said gas mass spectrometer sample (s) standard (s) having a rate of oxygen other than the oxygen levels of said first and second measurements, said additional measurement (s) measuring the ratio of the sulfur dioxide and oxygen ion masses per unit of time, which allows to obtain one (or more) other constant (s) or slope (s) of the linear relationship between said ratio and the concentration of sulfur dioxide.   3. A method for evaluating the oil consumption of an engine by tracing sulfur dioxide by means of a mass spectrometer, characterized in that it comprises the following steps: - the mass spectrometer is calibrated according to the method of any one of claims 1 or 2, so as to obtain the straight line beam giving the evolution of the dimensionless ratio between the mass of ions per unit of time of sulfur dioxide and the mass of ions by unit of oxygen time as a function of the number of the sulfur dioxide concentration for a given oxygen level, the number of strokes per second of sulfur dioxide is measured by mass spectrometry; also by mass spectrometry, the number of strokes / seconds of oxygen, the ratio between the number of strokes per second of sulfur dioxide and the number of strokes per second of oxygen is determined, the rate of oxygen, by means of an oxygen sensor, determine the right line among said line of lines, depending on the measured oxygen level, the concentration of sulfur dioxide is then obtained.   4. Device for calibrating a mass spectrometer for carrying out the method according to any one of claims 1, 2 or 3, characterized in that it comprises: a mass spectrometer, a probe Oxygen at the entrance of the mass spectrometer to measure the rate of 02.   at least one flow meter at the level of the conditioning line, so as to control the quantities of standard sample gas injected into the mass spectrometer.   5. Calibration device of a mass spectrometer according to claim 4, characterized in that said flow meter is positioned at the input of the mass spectrometer.   6. Device for calibrating a mass spectrometer according to claim 4, used for the tracing of sulfur dioxide on an evaluation bench of the oil consumption of an engine, characterized in that said flow meter is positioned. upstream of the furnace used in the oxidation of sulfur.