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FAQ titration (I)
Select your question:
In the following, our experts are explaining to the most common questions concerning titration in general.
Select your Question
What is titration? What are the advantages of titration? In which industries or segments is titration used? What is an autotitrator? How does an autotitrator work? What is the historical development of autotitrators? Which types of chemical reactions are used in titration? What are the indication methods used in titration? What is the difference between the symmetric and the asymmetric evaluation principle? Are there other evaluation principles used in the titrator? How can one speed-up the titrant addition (incremental vs. dynamic)? What is the difference between endpoint and equivalence point titration?What is titration?
Titration is an analytical technique which allows the quantitative determination of a specific substance (analyte) dissolved in a sample. It is based on a complete chemical reaction between the analyte and a reagent (titrant) of known concentration which is added to the sample:
Analyte + Reagent(Titrant) -> Reaction Products
The titrant is added until the reaction is complete. In order to be suitable for a determination, the end of the titration reaction has to be easily observable. This means that the reaction has to be monitored (indicated) by appropriate techniques, e.g. potentiometry (potential measurement with a sensor) or with colour indicators. The measurement of the dispensed titrant volume allows the calculation of the analyte content based on the stoichiometry of the chemical reaction. The reaction involved in a titration must be fast, complete, unambiguous and observable.
A well-known example is the titration of acetic acid in vinegar with sodium hydroxide.
Titration is an analytical technique which allows the quantitative determination of a specific substance (analyte) dissolved in a sample. It is based on a complete chemical reaction between the analyte and a reagent (titrant) of known concentration which is added to the sample:
Analyte + Reagent(Titrant) -> Reaction Products
The titrant is added until the reaction is complete. In order to be suitable for a determination, the end of the titration reaction has to be easily observable. This means that the reaction has to be monitored (indicated) by appropriate techniques, e.g. potentiometry (potential measurement with a sensor) or with colour indicators. The measurement of the dispensed titrant volume allows the calculation of the analyte content based on the stoichiometry of the chemical reaction. The reaction involved in a titration must be fast, complete, unambiguous and observable.
A well-known example is the titration of acetic acid in vinegar with sodium hydroxide.
What are the advantages of titration?
+ Classical, well-known analytical technique
+ Fast
+ Very accurate and precise technique
+ High degree of automation
+ Good price/performance ratio compared to more sophisticated techniques
+ It can be used by low-skilled and trained operators
+ No need for highly specialised chemical knowledge
+ Classical, well-known analytical technique
+ Fast
+ Very accurate and precise technique
+ High degree of automation
+ Good price/performance ratio compared to more sophisticated techniques
+ It can be used by low-skilled and trained operators
+ No need for highly specialised chemical knowledge
In which industries or segments is titration used?
A non-comprehensive listing of industries using titration:
Car Manufacturing, Ceramics, Chemical industry, Coal products, Coating, Cosmetics
Detergents
Electronic, Electroplating, Energy, Explosives
Food
Glass, Government
Health
Leather
Machinery
Packing materials, Paints, Pigments, Paper&Pulp, Petroleum, Pharmaceuticals, Photo, Plastic products, Printing & Publishing
Rail, Rubber
Stone (Clay, Cement)
Textile, Tobacco
Water
Zeolite
A non-comprehensive listing of industries using titration:
Car Manufacturing, Ceramics, Chemical industry, Coal products, Coating, Cosmetics
Detergents
Electronic, Electroplating, Energy, Explosives
Food
Glass, Government
Health
Leather
Machinery
Packing materials, Paints, Pigments, Paper&Pulp, Petroleum, Pharmaceuticals, Photo, Plastic products, Printing & Publishing
Rail, Rubber
Stone (Clay, Cement)
Textile, Tobacco
Water
Zeolite
What is an autotitrator?
Automated titrators are microprocessor-controlled instruments which allow the automation of all operations involved in titration:
1. Titrant addition
2. Monitoring of the reaction (Signal acquisition)
3. Recognition of the endpoint
4. Data storage
5. Calculation
6. Results storage
7. Transfer of data to printer or computer/external system
Automated titrators are microprocessor-controlled instruments which allow the automation of all operations involved in titration:
1. Titrant addition
2. Monitoring of the reaction (Signal acquisition)
3. Recognition of the endpoint
4. Data storage
5. Calculation
6. Results storage
7. Transfer of data to printer or computer/external system
How does an autotitrator work?
Automated titrators follow a defined sequence of operations. This sequence is basically the same for all different models and brands. It is performed and repeated several times until the endpoint or the equivalence point of the titration reaction is reached (titration cycle). The titration cycle consists mainly of 4 steps:
1. Titrant addition
2. Titration reaction
3. Signal acquisition
4. Evaluation
Each step has different specific parameters (e.g. increment size) which have to be defined according to the specific titration application. More complex applications require more steps, e.g. dispensing of an additional reagent for back titrations, dilution, adjusting of the pH value. These steps and the corresponding parameters are resumed in a titration method.
Automated titrators follow a defined sequence of operations. This sequence is basically the same for all different models and brands. It is performed and repeated several times until the endpoint or the equivalence point of the titration reaction is reached (titration cycle). The titration cycle consists mainly of 4 steps:
1. Titrant addition
2. Titration reaction
3. Signal acquisition
4. Evaluation
Each step has different specific parameters (e.g. increment size) which have to be defined according to the specific titration application. More complex applications require more steps, e.g. dispensing of an additional reagent for back titrations, dilution, adjusting of the pH value. These steps and the corresponding parameters are resumed in a titration method.
What is the historical development of autotitrators?
The classical way:
Titration is a classical analytical technique widely used. Originally, it was performed by adding the titrant using a graduated glass cylinder (burette). With a tap the titrant addition was regulated manually. A change in colour indicated the end of the titration reaction (endpoint). At first, only those titrations showing a significant colour change upon reaching the endpoint were performed. Later titrations were coloured artificially with an indicator dye. The precision achieved depended mainly on the chemist's skills and, in particular, on his different colour perception.The modern way:
Titration has experienced a strong development: manual and -later- motorized piston burettes allow reproducible and accurate titrant addition. Electrodes for potential measurement replace the colour indicators, achieving higher precision and accuracy of the results. Graphical plot of potential versus titrant volume allows a more exact statement about the reaction than the colour change at the endpoint. With microprocessors the titration can be controlled and evaluated automatically. This represents a relevant step towards complete automation.
Today and tomorrow:
Developmentis not yet complete. Modern autotitrators allow the definition of complete analysis sequences achieving maximum flexibility in method development. For each application the specific method can be defined by combining simple operation functions like "Dose", "Stir", "Titrate", "Calculate" in a defined sequence. Auxiliary instruments (sample changers, pumps) help in reducing and simplifying the work load in laboratories. A further trend is the connection to computers and Laboratory Information Management Systems (LIMS).
The classical way:
Titration is a classical analytical technique widely used. Originally, it was performed by adding the titrant using a graduated glass cylinder (burette). With a tap the titrant addition was regulated manually. A change in colour indicated the end of the titration reaction (endpoint). At first, only those titrations showing a significant colour change upon reaching the endpoint were performed. Later titrations were coloured artificially with an indicator dye. The precision achieved depended mainly on the chemist's skills and, in particular, on his different colour perception.The modern way:
Titration has experienced a strong development: manual and -later- motorized piston burettes allow reproducible and accurate titrant addition. Electrodes for potential measurement replace the colour indicators, achieving higher precision and accuracy of the results. Graphical plot of potential versus titrant volume allows a more exact statement about the reaction than the colour change at the endpoint. With microprocessors the titration can be controlled and evaluated automatically. This represents a relevant step towards complete automation.
Today and tomorrow:
Developmentis not yet complete. Modern autotitrators allow the definition of complete analysis sequences achieving maximum flexibility in method development. For each application the specific method can be defined by combining simple operation functions like "Dose", "Stir", "Titrate", "Calculate" in a defined sequence. Auxiliary instruments (sample changers, pumps) help in reducing and simplifying the work load in laboratories. A further trend is the connection to computers and Laboratory Information Management Systems (LIMS).
Which types of chemical reactions are used in titration?
There are several assay reactions which are used in titration:
Acid/Base reactions:
Examples: Acid content in wine, milk. Acid content in ketchup. Content of inorganic acids like sulfuric acid.
Precipitation reactions:
Examples: Salt content in crisps, ketchup and food; Silver content in coins,
Sulfate content in mineral water; Sulfate content in electroplating bath
Redox reactions:
Examples: Content of copper, chromium and nickel in electroplating baths
Complexometric reactions:
Examples: Total hardness of water (Mg and Ca); Calcium content in milk and cheese; Cement analysis
Colloidalprecipitation reaction:
Examples: Anionic surfactant content in detergents; Anionic surfactant content in washing powders; Anionic surfactant content in liquid cleanser.
There are several assay reactions which are used in titration:
Acid/Base reactions:
Examples: Acid content in wine, milk. Acid content in ketchup. Content of inorganic acids like sulfuric acid.
Precipitation reactions:
Examples: Salt content in crisps, ketchup and food; Silver content in coins,
Sulfate content in mineral water; Sulfate content in electroplating bath
Redox reactions:
Examples: Content of copper, chromium and nickel in electroplating baths
Complexometric reactions:
Examples: Total hardness of water (Mg and Ca); Calcium content in milk and cheese; Cement analysis
Colloidalprecipitation reaction:
Examples: Anionic surfactant content in detergents; Anionic surfactant content in washing powders; Anionic surfactant content in liquid cleanser.
What are the indication methods used in titration?
Titrations can be classified according to the indication principles and the chemical reaction occurring:
Potentiometry:
The concentration-dependent potential (mV) of a solution is measured against a reference potential.
Examples: Acid/Base (aqueous/non-aqueous), redox, precipitation reactions.
Voltametry:
The concentration-dependent potential of a solution (mV) is measured at a constant polarizing electric current.
Examples: Karl Fischer water determination.
Amperometry:
The current flowing in a sample solution (µA) is measured at a constant polarizing potential.
Examples: Iron(II) and Vitamin C determination.
Photometry:
The light transmission (mV or % transmission) of a coloured or turbid solution is measured with a photometric sensor.
Examples: Complexometric and turbidimetric reactions.
Conductivity:
The conductivity of a solution (µS/cm) is measured by a conductivity meter.
Example: Alpha acids in beer.
Thermometry:
The temperature of a sample is measured by a temperature sensor.
Example: Boric acid content.
Titrations can be classified according to the indication principles and the chemical reaction occurring:
Potentiometry:
The concentration-dependent potential (mV) of a solution is measured against a reference potential.
Examples: Acid/Base (aqueous/non-aqueous), redox, precipitation reactions.
Voltametry:
The concentration-dependent potential of a solution (mV) is measured at a constant polarizing electric current.
Examples: Karl Fischer water determination.
Amperometry:
The current flowing in a sample solution (µA) is measured at a constant polarizing potential.
Examples: Iron(II) and Vitamin C determination.
Photometry:
The light transmission (mV or % transmission) of a coloured or turbid solution is measured with a photometric sensor.
Examples: Complexometric and turbidimetric reactions.
Conductivity:
The conductivity of a solution (µS/cm) is measured by a conductivity meter.
Example: Alpha acids in beer.
Thermometry:
The temperature of a sample is measured by a temperature sensor.
Example: Boric acid content.
What is the difference between the symmetric and the asymmetric evaluation principle?
Symmetric curve:
The curve has a symmetric profile and the equivalence point is the inflection point of the curve.
This curve is evaluated by plotting the first derivative dE/dV versus titrant consumption V. The maximum of the derivative is at the inflection point and indicates the equivalence point.
For the automatic evaluation of the symmetric S-curve the titrator provides the appropriate procedure ("STANDARD").
Examples: Acid/base titrations, redox titrations, precipitation titrations
Asymmetric curve:
This titration curve shows a different profile than the typical symmetric S-curve, and thus a different evaluation procedure is needed. This is based on the Tubbs procedure (see "Fundamentals of titration", ME-704153).
The asymmetry has to be taken into account for curve evaluation. The equivalence point is shifted towards the region with the stronger curvature.
The curve is fitted with two circles (better: two hyperbolas). The intersection point of the line connecting the two foci and the titration curve indicates the equivalence point.
Examples: Photometric titrations, redox titrations, turbidimetric titrations
Symmetric curve:
The curve has a symmetric profile and the equivalence point is the inflection point of the curve.
This curve is evaluated by plotting the first derivative dE/dV versus titrant consumption V. The maximum of the derivative is at the inflection point and indicates the equivalence point.
For the automatic evaluation of the symmetric S-curve the titrator provides the appropriate procedure ("STANDARD").
Examples: Acid/base titrations, redox titrations, precipitation titrations
Asymmetric curve:
This titration curve shows a different profile than the typical symmetric S-curve, and thus a different evaluation procedure is needed. This is based on the Tubbs procedure (see "Fundamentals of titration", ME-704153).
The asymmetry has to be taken into account for curve evaluation. The equivalence point is shifted towards the region with the stronger curvature.
The curve is fitted with two circles (better: two hyperbolas). The intersection point of the line connecting the two foci and the titration curve indicates the equivalence point.
Examples: Photometric titrations, redox titrations, turbidimetric titrations
Are there other evaluation principles used in the titrator?
Four different curves can be observed and evaluated with the corresponding procedures specified in the titration method.
Symmetric curve (see answer above)
Asmmetric curve (see answer above)
Minimum (Maximum) curve:
This curve shows the typical profile obtained from turbidimetric titrations, e.g., determination of the anionic surfactant content, where a colloidal precipitate is formed by adding the titrant. This leads to an increased turbidity of the solution. The profile of the curve is characterized by a minimum in the curve which indicates the equivalence point EQP. The precipitate formation is monitored with a photometric sensor, and the light transmission in the solution is measured with a phototrode. At the equivalence point, the turbidity reaches its maximum, i.e. the transmission has a minimum. A special evaluation procedure allows the determination of the minimum of the curve ("MINIMUM"). Curves showing a maximum are evaluated with the procedure "MAXIMUM". Example: Content determination of anionic surfactants in cooling lubricants.
Examples: Ionic surfactant determination (turbidimetric titrations).
Segmented curve:
The profile of this curve shows a clear bend at the equivalence point. This profile is obtained when conductometric titrations are performed (notice the unit of measurement in the graphical representation: S/cm, micro-Siemens). The EQP is defined by a sharp change in conductivity. The curve is evaluated by determining the maximum of its second derivative.
Examples: alpha-Acids in beer (conductometric titration), Vitamin C (amperometric det.).
Four different curves can be observed and evaluated with the corresponding procedures specified in the titration method.
Symmetric curve (see answer above)
Asmmetric curve (see answer above)
Minimum (Maximum) curve:
This curve shows the typical profile obtained from turbidimetric titrations, e.g., determination of the anionic surfactant content, where a colloidal precipitate is formed by adding the titrant. This leads to an increased turbidity of the solution. The profile of the curve is characterized by a minimum in the curve which indicates the equivalence point EQP. The precipitate formation is monitored with a photometric sensor, and the light transmission in the solution is measured with a phototrode. At the equivalence point, the turbidity reaches its maximum, i.e. the transmission has a minimum. A special evaluation procedure allows the determination of the minimum of the curve ("MINIMUM"). Curves showing a maximum are evaluated with the procedure "MAXIMUM". Example: Content determination of anionic surfactants in cooling lubricants.
Examples: Ionic surfactant determination (turbidimetric titrations).
Segmented curve:
The profile of this curve shows a clear bend at the equivalence point. This profile is obtained when conductometric titrations are performed (notice the unit of measurement in the graphical representation: S/cm, micro-Siemens). The EQP is defined by a sharp change in conductivity. The curve is evaluated by determining the maximum of its second derivative.
Examples: alpha-Acids in beer (conductometric titration), Vitamin C (amperometric det.).
How can one speed-up the titrant addition (incremental vs. dynamic)?
Incremental titrant addition (INC)
The titrant is added in constant volume increments dV. Incremental titrant addition is used in non-aqueous titrations, which sometimes have an unstable signal, and also in redox and in photometric titrations, where the potential jump at the equivalence point occurs suddenly. Notice that in the steepest region of the curve there are relatively few measured points.
Dynamic titrant addition (DYN)
A constant pH- or potential change per increment allows the variation of the volume increment between minimum and maximum volume increment.
Thus, the analysis can be speeded up by using big increments in the flat regions of the titration curve. In addition, more measured points are obtained in the steepest region of the curve leading to a more accurate evaluation.
Incremental titrant addition (INC)
The titrant is added in constant volume increments dV. Incremental titrant addition is used in non-aqueous titrations, which sometimes have an unstable signal, and also in redox and in photometric titrations, where the potential jump at the equivalence point occurs suddenly. Notice that in the steepest region of the curve there are relatively few measured points.
Dynamic titrant addition (DYN)
A constant pH- or potential change per increment allows the variation of the volume increment between minimum and maximum volume increment.
Thus, the analysis can be speeded up by using big increments in the flat regions of the titration curve. In addition, more measured points are obtained in the steepest region of the curve leading to a more accurate evaluation.
What is the difference between endpoint and equivalence point titration?
Endpoint titration mode (EP):
The endpoint mode represents the classical titration procedure: the titrant is added until the end of the reaction is observed, e.g., by a colour change of an indicator. With an automatic titrator, the sample is titrated until a predefined value is reached, e.g. pH = 8.2.
Equivalence point titration mode (EQP):
The equivalence point is the point at which the analyte and the reagent are present in exactly the same concentration. In most cases it is virtually identical to the inflection point of the titration curve, e.g. titration curves obtained from acid/base titrations.
The inflection point of the curve is defined by the corresponding pH or potential (mV) value and titrant consumption (mL). The equivalence point is calculated from the consumption of titrant of known concentration. The product of concentration and the titrant consumption gives the amount of substance which has reacted with the sample. In an autotitrator the measured points are evaluated according to specific mathematical procedures which lead to an evaluated titration curve. The equivalence point is then calculated from this evaluated curve.
Endpoint titration mode (EP):
The endpoint mode represents the classical titration procedure: the titrant is added until the end of the reaction is observed, e.g., by a colour change of an indicator. With an automatic titrator, the sample is titrated until a predefined value is reached, e.g. pH = 8.2.
Equivalence point titration mode (EQP):
The equivalence point is the point at which the analyte and the reagent are present in exactly the same concentration. In most cases it is virtually identical to the inflection point of the titration curve, e.g. titration curves obtained from acid/base titrations.
The inflection point of the curve is defined by the corresponding pH or potential (mV) value and titrant consumption (mL). The equivalence point is calculated from the consumption of titrant of known concentration. The product of concentration and the titrant consumption gives the amount of substance which has reacted with the sample. In an autotitrator the measured points are evaluated according to specific mathematical procedures which lead to an evaluated titration curve. The equivalence point is then calculated from this evaluated curve.