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Determination of Water Content in Rice 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

Cereals and starchy products such as wheat flour, rice or noodles contain very strongly bonded water in their cellular structures. In order to fully extract the water during KF titration, the samples must be crushed to fine powder prior to analysis. The presence of formamide during the direct volumetric determination increases the extraction of water. Alternatively, titration may be carried out under warm conditions (50 °C). The use of a homogeniser is also favourable. After water determination it is mandatory that both the cell and the indicator electrode be carefully cleansed. The coulometric method can only be applied in combination with KF oven technology. For the release of water a temperature of 110 °C is recommended (disintegration at higher temperatures).

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
or
40 mL / 20 mL 188009 / 109684 Aquastar™ - CombiMethanol / Formamide - solvent mixture for one component titration

Titration Parameters:
Extraction time: 180 sec.
Temperature: 50 °C
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.2 g (as a fine powder)

Procedure:
The titration medium is first placed into the cell, heated up to 50 °C and titrated dry by means of the titrant. Then the sample is added from a weighing boat (exact sample weight determination by weighing of weighing boat before and after addition) and the titration is started. For complete extraction of the water a stirring time of 180 seconds is recommended.

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
or
40 mL / 20 mL 188015 / 109684 Aquastar™ - Solvent / Formamide - solvent mixture for two component titration

Titration Parameters:
Extraction time: 180 sec.
Temperature: 50 °C
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.2 g (as a fine powder)

Procedure:
The titration medium is first placed into the cell, heated up to 50 °C and titrated dry by means of the titrant. Then the sample is added from a weighing boat (exact sample weight determination by weighing of weighing boat before and after addition) and the titration is started. For complete extraction of the water a stirring time of 180 seconds is recommended.

Materials

     
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