Determination of Water Content in Coffee extract (Instant Coffee) 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
Coffee extracts contain very firmly bonded water. Extraction in methanol is very slow and dragging. The presence of formamide and salicylic acid accelerate the release of water (by DIN method). Additionally, titration under warm conditions as well as the use of a homogeniser are favourable. Alternatively the KF oven technique can be used in combination with coulometry. For the release of water a temperature of ca. 105 °C is recommended.
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
40 mL 188009 Aquastar® - CombiMethanol - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water
and
20 mL / 12 g 109684 / 100635 Formamide / salicylic acid - null
Titration Parameters:
Extraction time: 180 sec.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min
Sample size:
0.3 - 0.5 g
Procedure:
The titration medium is first placed into the cell 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 dissolution of the sample a stirring time of three minutes 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
40 mL 188015 Aquastar® - Solvent - Solvent for volumetric titration with two component reagents
and
20 mL / 12 g 109684 / 100635 Formamide / salicylic acid - null
Titration Parameters:
Extraction time: 180 sec.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min
Sample size:
0.3 - 0.5 g
Procedure:
The titration medium is first placed into the cell 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 dissolution of the sample a stirring time of three minutes is recommended.