CA2173904C - A procedure for determining the type and quantity of a substance that can be converted electrochemically and that is contained in a gas sample - Google Patents
A procedure for determining the type and quantity of a substance that can be converted electrochemically and that is contained in a gas sample Download PDFInfo
- Publication number
- CA2173904C CA2173904C CA 2173904 CA2173904A CA2173904C CA 2173904 C CA2173904 C CA 2173904C CA 2173904 CA2173904 CA 2173904 CA 2173904 A CA2173904 A CA 2173904A CA 2173904 C CA2173904 C CA 2173904C
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- substance
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
- G01N33/483—Physical analysis of biological material
- G01N33/497—Physical analysis of biological material of gaseous biological material, e.g. breath
- G01N33/4972—Determining alcohol content
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- Molecular Biology (AREA)
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- Biomedical Technology (AREA)
- Food Science & Technology (AREA)
- Urology & Nephrology (AREA)
- Hematology (AREA)
- Biophysics (AREA)
- Medicinal Chemistry (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
Abstract
A procedure for determining the type and quantity of a substance that can be converted electrochemically and that is contained in a gas sample, which generates a physical process variable in a measuring cell, is to be improved such that is can be used quickly and in a manner that is replicable. In order that this can be done, provision is made such that the process variable that changes over time is the current strength; and in that the type and quantity of the electrochemically convertible substance is determined from the linearly matched relation of current strength and flowed charged in a time frame after the maximum value of the current strength has been achieved.
Description
i A Procedure for Determining the Type and Quantity of a Substance that can be Converted Electrochemically and that is Contained in a Gas Sample The present invention relates to a procedure for determining the type and quantity of a substance that can be converted electrochemically and that is contained in a gas sample, which generates a physical process variable in a measuring cell, said process variable changing over time, and rising from a base line to a maximum value and then returning once again to the base line.
An apparatus for measuring the concentration of alcohol as the substance in the breath that is to be indicated is described in U.S. 4.770.026. In this known apparatus, a gas sample with an alcohol-vapor component acts on a fuel cell, and the physical process variable i(t) that is obtained by electrochemical conversion is passed to an analysis circuit that determines a value that is proportional to the alcohol vapor concentration by integrating the signal pattern of the physical process variable over time. When alcohol vapor acts on the measuring cell, the measured signal increases, starting from a base line, passes through a maximum value I max and returns to the minimal value that is close to the base line after the complete electro-chemical conversion of the alcohol molecules. The area that is enclosed between the function value of the measured signal and 2173904 ~ ~~
the base line represents the flowed electrical charge and is proportional to the quantity and concentration of the alcohol vapor in the gas sample.
In the known measuring cell, the shape of the curve of the measured signal changes as the measuring cell ages, i.e., the curve becomes flatter and wider during the period of use. A
similar change in the shape of~the curve of the measured signal can occur after a number of short measurement cycles that follow closely one after the others these changes to the signal are reversible, at least in part, after a lengthy recuperation phase.
Since integration is carried out over almost the whole course of the measured signal in order to determine the concentration component of the alcohol vapor in the gas sample, changes to the shape of the curve will affect the content of the area and will thus have an effect on measurement precision, so that repeated calibration cycles using a gas sample containing a known concentration of alcohol have to be carried out. Such calibration cycles make it more difficult to use the apparatus, particularly if the measurement cell has to be gassed at frequent intervals.
In addition, in the known analysis process, the composition of the substance that is to be indicated is known. Accompanying substances, such as methanol or acetone, are not recognized during this kind of analysis.
An apparatus for measuring the concentration of alcohol as the substance in the breath that is to be indicated is described in U.S. 4.770.026. In this known apparatus, a gas sample with an alcohol-vapor component acts on a fuel cell, and the physical process variable i(t) that is obtained by electrochemical conversion is passed to an analysis circuit that determines a value that is proportional to the alcohol vapor concentration by integrating the signal pattern of the physical process variable over time. When alcohol vapor acts on the measuring cell, the measured signal increases, starting from a base line, passes through a maximum value I max and returns to the minimal value that is close to the base line after the complete electro-chemical conversion of the alcohol molecules. The area that is enclosed between the function value of the measured signal and 2173904 ~ ~~
the base line represents the flowed electrical charge and is proportional to the quantity and concentration of the alcohol vapor in the gas sample.
In the known measuring cell, the shape of the curve of the measured signal changes as the measuring cell ages, i.e., the curve becomes flatter and wider during the period of use. A
similar change in the shape of~the curve of the measured signal can occur after a number of short measurement cycles that follow closely one after the others these changes to the signal are reversible, at least in part, after a lengthy recuperation phase.
Since integration is carried out over almost the whole course of the measured signal in order to determine the concentration component of the alcohol vapor in the gas sample, changes to the shape of the curve will affect the content of the area and will thus have an effect on measurement precision, so that repeated calibration cycles using a gas sample containing a known concentration of alcohol have to be carried out. Such calibration cycles make it more difficult to use the apparatus, particularly if the measurement cell has to be gassed at frequent intervals.
In addition, in the known analysis process, the composition of the substance that is to be indicated is known. Accompanying substances, such as methanol or acetone, are not recognized during this kind of analysis.
DE-43 44 196 refers to a determination procedure of this kind, in which quantitative statements with respect to the quantity and type of the substance that is to be indicated are meant to be made with the help of integration across sections of the curve for the process value.
All known analysis procedures suffer from disadvantages, in particular the high computing costs for the integration procedure in particular, and the way in Which the shape of the curve depends on the age of the sensor, on temperature and on marginal effects. No accompanying substances are identified, and neither are deviant shapes of the curve that may be attributable to faulty sensors or defective equipment.
It is the task of the present invention to so improve an analysis procedure for electrochemical measuring cells that the type and quantity of a substance in the gas sample, Which can be electrochemically converted, can be determined rapidly and in a manner that can be replicated.
According to a broad aspect, the present invention provides a method for determining the type and/or amount of an electrochemically convertible substance in a gas sample, which method comprises subjecting the substance in the sample to electrochemical conversion in a measuring cell to produce a currant whose intensity changes over time in that it rises from a reference value to a maximum value and then falls back to the reference value again, wherein at least one of the type and amount of the substance is established from a linear relationship between the currant intensity and the charge that has flo'ved in the time period after the maximum value of the currant intensity has been reached.
An important advantage of the present invention is that the linear connection bet'veen current strength and floraed charge - 3a -makes it very simple to determine the type and quantity of the substance that is to be indicated. Furthermore, temperature and aging effects are reduced during the determination, since only the linear area of the measured curve in the time frame directly after the maximal value is used as a basis for the current strength.
Most surprisingly, it has now been found that the Coulometric analysis procedure and its underlying theory, formerly used in for liquid samples, can also be used in the gas phase. This means, in particular, that current strength and flowed charge are in a linear relationship; that the total flowed charge can be determined from the condition of current strength equals zero from the corresponding linear equation/lines: and that, finally, the quantity/concentration of the substance in the gas sample can be determined from the total flowed charge. A description of the known theory can be found, for example, R. Greef et al., Instrumental Methods in Electrochemistry, 1985, pp. 44-47.
In particular, the determination of ethanol in gas samples has been examined as a known area of application for the present invention.
Figure 1 shows a typical measurement curve for the current strength I (in uA) ("sensor current") as a function of the time t (in s) for the determination of ethanol with an electrochemical sensor.
If one now measures current strength I (in uA) as a function of the flowed charge Q (in uC), as is shown graphically in Figure 2 for a 2- and 3-electrode operation of an electrochemical measuring cell (reference number 2:2 - electrode operation;
reference number l:3 - electrode operation), on linear matching of the section of the curve behind the maximum one obtains the total charge that has flowed because of the electrochemical conversion of the ethanol. This follows from the theoretical condition for potential-controlled Coulometry, to the effect that in the case of a linear relation between current strength and charge, the total flowed charge results from the condition current strength equals zero on the charge axis. This applies in to a specific measuring cell in each instance. In the example that is shown in Figure 2, the slope of the linear section behind the maximum is identical for both curves, which is obviously an "indicator" for the identical measured substance. The regression lines are numbered 3. Further on, the slope of the curve and shape of the curve change, which could be an indication of continuing or subsequent electrochemical reactions of the ethanol, expressed for the three-electrode sensor (curve 1).
Taken all in all, the measurements corroborate the fact that the linearly matched section of the curve behind the maximum is substance specific, which is to say that the presence of additional substances that affect the measurement method, e.g., methanol, results in a modified slope of the line, and can be recognized thereby. Parallel lines result for a substance, e.g., ethanol, for different measuring cells. The total flowed charge quantity is thus different, as can be seen from Figure 2. The correlation coefficient for the regression lines 3 is an indication of the quality of the sensors and can thus serve to check their function.
In comparison to the prior art, the present procedure permits considerably faster and more reliable evaluation of measurements, since the line equation can be computed with fewer measurement points and it is no longer necessary to go through the whole evaluation.
In practical application, the evaluation of the measurement and the computation of the concentration of the substance to be examined that is ultimately desired can be effected with the help of suitable electronic components, in particular by using a microprocessor.
All known analysis procedures suffer from disadvantages, in particular the high computing costs for the integration procedure in particular, and the way in Which the shape of the curve depends on the age of the sensor, on temperature and on marginal effects. No accompanying substances are identified, and neither are deviant shapes of the curve that may be attributable to faulty sensors or defective equipment.
It is the task of the present invention to so improve an analysis procedure for electrochemical measuring cells that the type and quantity of a substance in the gas sample, Which can be electrochemically converted, can be determined rapidly and in a manner that can be replicated.
According to a broad aspect, the present invention provides a method for determining the type and/or amount of an electrochemically convertible substance in a gas sample, which method comprises subjecting the substance in the sample to electrochemical conversion in a measuring cell to produce a currant whose intensity changes over time in that it rises from a reference value to a maximum value and then falls back to the reference value again, wherein at least one of the type and amount of the substance is established from a linear relationship between the currant intensity and the charge that has flo'ved in the time period after the maximum value of the currant intensity has been reached.
An important advantage of the present invention is that the linear connection bet'veen current strength and floraed charge - 3a -makes it very simple to determine the type and quantity of the substance that is to be indicated. Furthermore, temperature and aging effects are reduced during the determination, since only the linear area of the measured curve in the time frame directly after the maximal value is used as a basis for the current strength.
Most surprisingly, it has now been found that the Coulometric analysis procedure and its underlying theory, formerly used in for liquid samples, can also be used in the gas phase. This means, in particular, that current strength and flowed charge are in a linear relationship; that the total flowed charge can be determined from the condition of current strength equals zero from the corresponding linear equation/lines: and that, finally, the quantity/concentration of the substance in the gas sample can be determined from the total flowed charge. A description of the known theory can be found, for example, R. Greef et al., Instrumental Methods in Electrochemistry, 1985, pp. 44-47.
In particular, the determination of ethanol in gas samples has been examined as a known area of application for the present invention.
Figure 1 shows a typical measurement curve for the current strength I (in uA) ("sensor current") as a function of the time t (in s) for the determination of ethanol with an electrochemical sensor.
If one now measures current strength I (in uA) as a function of the flowed charge Q (in uC), as is shown graphically in Figure 2 for a 2- and 3-electrode operation of an electrochemical measuring cell (reference number 2:2 - electrode operation;
reference number l:3 - electrode operation), on linear matching of the section of the curve behind the maximum one obtains the total charge that has flowed because of the electrochemical conversion of the ethanol. This follows from the theoretical condition for potential-controlled Coulometry, to the effect that in the case of a linear relation between current strength and charge, the total flowed charge results from the condition current strength equals zero on the charge axis. This applies in to a specific measuring cell in each instance. In the example that is shown in Figure 2, the slope of the linear section behind the maximum is identical for both curves, which is obviously an "indicator" for the identical measured substance. The regression lines are numbered 3. Further on, the slope of the curve and shape of the curve change, which could be an indication of continuing or subsequent electrochemical reactions of the ethanol, expressed for the three-electrode sensor (curve 1).
Taken all in all, the measurements corroborate the fact that the linearly matched section of the curve behind the maximum is substance specific, which is to say that the presence of additional substances that affect the measurement method, e.g., methanol, results in a modified slope of the line, and can be recognized thereby. Parallel lines result for a substance, e.g., ethanol, for different measuring cells. The total flowed charge quantity is thus different, as can be seen from Figure 2. The correlation coefficient for the regression lines 3 is an indication of the quality of the sensors and can thus serve to check their function.
In comparison to the prior art, the present procedure permits considerably faster and more reliable evaluation of measurements, since the line equation can be computed with fewer measurement points and it is no longer necessary to go through the whole evaluation.
In practical application, the evaluation of the measurement and the computation of the concentration of the substance to be examined that is ultimately desired can be effected with the help of suitable electronic components, in particular by using a microprocessor.
Claims (5)
1. A method for determining the type and/or amount of an electrochemically convertible substance in a gas sample, which method comprises subjecting the substance in the sample to electrochemical conversion in a measuring cell to produce a current whose intensity changes over time in that it rises from a reference value to a maximum value and than falls back to the reference value again, wherein at least one of the type and amount of the substance is established from a linear relationship between the current intensity and the charge that has flowed in the time period after the maximum value of the currant intensity has been reached.
2. A method according to claim 1, wherein the total amount of charge that has flowed, and thus the amount of the substance, which is directly proportional thereto, are established from the linear relationship between the currant intensity and the charge that has flowed as a value corresponding to a current intensity of zero.
3. A method according to claim 1 or 2, wherein, from the linear relationship between the current intensity and the charge that has flowed, a proportionality constant is used to determine the type of the substance.
4. A method according to any of claims 1 to 3, wherein the relationship between the currant intensity and the charge that has flowed is effected with the aid of a microprocessor.
5. A method according to any of claims 1 to 4, wherein the electrochemically convertible substance is ethanol, methanol or a mixture of ethanol and methanol.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19514215.2-52 | 1995-04-15 | ||
| DE1995114215 DE19514215C2 (en) | 1995-04-15 | 1995-04-15 | Method for determining the type and amount of an electrochemically convertible substance in a gas sample |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2173904A1 CA2173904A1 (en) | 1996-10-16 |
| CA2173904C true CA2173904C (en) | 2000-02-01 |
Family
ID=7759763
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2173904 Expired - Fee Related CA2173904C (en) | 1995-04-15 | 1996-04-11 | A procedure for determining the type and quantity of a substance that can be converted electrochemically and that is contained in a gas sample |
Country Status (5)
| Country | Link |
|---|---|
| AU (1) | AU675765B2 (en) |
| CA (1) | CA2173904C (en) |
| DE (1) | DE19514215C2 (en) |
| FR (1) | FR2733054B1 (en) |
| GB (1) | GB2299864B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102004062051B4 (en) * | 2004-12-23 | 2011-07-14 | Dräger Safety AG & Co. KGaA, 23560 | Method for determining the concentration of a gas with an electrochemical gas sensor |
| ATE545022T1 (en) * | 2009-12-01 | 2012-02-15 | Draeger Safety Ag & Co Kgaa | METHOD FOR VERIFYING AN ELECTROCHEMICAL SUBSTANCE IN A GAS SAMPLE |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8330268D0 (en) * | 1983-11-12 | 1983-12-21 | Lion Lab Ltd | Discriminant analysis of gas constituents |
| US4770026A (en) * | 1987-01-15 | 1988-09-13 | Alcotek, Inc. | Method of and apparatus for testing breath alcohol |
| US5048321A (en) * | 1990-05-11 | 1991-09-17 | Intoximeters, Inc. | Method of discriminating breath contaminants and apparatus therefor |
| DE4344196C2 (en) * | 1993-12-23 | 1997-08-07 | Draegerwerk Ag | Method for determining parameters of an electrochemically convertible substance in a gas sample |
-
1995
- 1995-04-15 DE DE1995114215 patent/DE19514215C2/en not_active Expired - Fee Related
-
1996
- 1996-04-03 FR FR9604478A patent/FR2733054B1/en not_active Expired - Fee Related
- 1996-04-10 GB GB9607462A patent/GB2299864B/en not_active Expired - Fee Related
- 1996-04-11 AU AU50615/96A patent/AU675765B2/en not_active Ceased
- 1996-04-11 CA CA 2173904 patent/CA2173904C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE19514215C2 (en) | 1997-09-18 |
| AU675765B2 (en) | 1997-02-13 |
| GB2299864B (en) | 1997-03-19 |
| FR2733054B1 (en) | 1998-05-29 |
| DE19514215A1 (en) | 1996-10-24 |
| CA2173904A1 (en) | 1996-10-16 |
| GB9607462D0 (en) | 1996-06-12 |
| FR2733054A1 (en) | 1996-10-18 |
| GB2299864A (en) | 1996-10-16 |
| AU5061596A (en) | 1996-10-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |