Determination of Water Content in Tobacco Using Karl Fischer Titration

Product Group

Foodstuffs

General Information concerning the product group

Foodstuffs

Foodstuffs encompass the most diverse products. Depending on whether carbohydrate-rich, fatty or proteinrich substances are under investigation, different working techniques are favourable. Complex matrices that dissolve slowly, or where the water can only be slowly extracted, necessitate the use of solubilisers. In addition, titration under heating and the application of a homogeniser to accelerate water release are expedient.

Special Information concerning the sample and the methods

During direct volumetric analysis the slow extraction of water from tobacco leads to long titration times and dragging end points. The external extraction with methanol is therefore preferred. The water concentration of the extract may be determined both volumetrically as well as coulometrically.

Titration one component system

Reagents:

Titrant
188005 Aquastar™ - CombiTitrant 5 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 5 mg water

Solvent
50 mL 188009 Aquastar™ - CombiMethanol - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
5 mL sample solution

Procedure:
Sample preparation: 1 g of the sample (m1) is accurately weighed into a 50 mL conical flask. After addition of 25 mL methanol (m2) the solution is stirred for one hour. KF titration: The titration medium is first placed into the titration cell and titrated dry by means of the titrant. An aliquote of the sample is injected with a syringe (exact sample weight determination by weighing of syringe before and after addtition) into the titration cell and the titration is started. The water concentration (W3) is then determined. Subsequently, the blank value of the solvent (W2) is determined. Calculation of the water concentration of the sample (W1) is carried out as follows: W1 = [W3 x (m1 + m2) - W2 x m2] / m1

Titration two component system

Reagents:

Titrant
188010 Aquastar™ - Titrant 5 - Titrant for volumetric titration with two component reagents, 1 mL = approx. 5 mg water

Solvent
50 mL 188015 Aquastar™ - Solvent - Solvent for volumetric titration with two component reagents

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
5 mL sample solution

Procedure:
Sample preparation: 1 g of the sample (m1) is accurately weighed into a 50 mL conical flask. After addition of 25 mL methanol (m2) the solution is stirred for one hour. KF titration: The titration medium is first placed into the titration cell and titrated dry by means of the titrant. An aliquote of the sample is injected with a syringe (exact sample weight determination by weighing of syringe before and after addition) into the titration cell and the titration is started. The water concentration (W3) is then determined. Subsequently, the blank value of the solvent (W2) is determined. Calculation of the water concentration of the sample (W1) is carried out as follows: W1 = [W3 x (m1 + m2) - W2 x m2] / m1

Coulometry with diaphragm

Reagents:

Catholyte
5 mL 109255 Aquastar™ - CombiCoulomat frit - Coulometric Karl Fischer reagent for cells with diaphragm

Anolyte
100 mL 109255 Aquastar™ - CombiCoulomat frit - Coulometric Karl Fischer reagent for cells with diaphragm

Titration Parameters:
Default coulometer settings for cell with diaphragm:
For end point indication, e.g.:
I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criterion: drift < 10 µg/min

Sample size:
1 mL sample solution

Procedure:
Sample preparation: 1 g of the sample (m1) is accurately weighed into a 50 mL conical flask. After addition of 25 mL methanol (m2) the solution is stirred for one hour. KF titration: The titration medium is first placed into the titration cell and titrated dry by means of the titrant. An aliquote of the sample is injected with a syringe (exact sample weight determination by weighing of syringe before and after addition) into the titration cell and the titration is started. The water concentration (W3) is then determined. Subsequently, the blank value of the solven (W2) is determined. Calculation of the water concentration of the sample (W1) is carried out as follows: W1 = [W3 x (m1 + m2) - W2 x m2] / m1

Coulometry without diaphragm

Reagents:

Working medium
100 mL 109257 Aquastar™ - CombiCoulomat fritless - Coulometric Karl Fischer reagent for cells with or without diaphragm

Titration Parameters:
Default coulometer settings for cell without diaphragm:
For end point indication, e.g.:
I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criterion: drift < 10 µg/min

Sample size:
1 mL sample solution

Procedure:
Sample preparation: 1 g of the sample (m1) is accurately weighed into a 50 mL conical flask. After addition of 25 mL methanol (m2) the solution is stirred for one hour. KF titration: The titration medium is first placed into the titration cell and titrated dry by means of the titrant. An aliquote of the sample is injected with a syringe (exact sample weight determination by weighing of syringe before and after addition) into the titration cell and the titration is started. The water concentration (W3) is then determined. Subsequently, the blank value of the solven (W2) is determined. Calculation of the water concentration of the sample (W1) is carried out as follows: W1 = [W3 x (m1 + m2) - W2 x m2] / m1

Materials

     
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