Flashcards in Lecture 5 - Moisture pt 2 Deck (48)
how is H2O removed via distillation method?
- with distillation solvents (toluene or mineral oil)
- vapor is cooled and water collected and measured
distillation solvents should be chemically (stable/unstable) at distillation temps.
what are the 2 versions of distillation solvents?
- volatile (toluene)
- nonvolatile (mineral oil)
distillation is a (direct/indirect) method of moisture determination
is the distillation technique AOAC approved?
distillation is more effective with (volatile/non-volatile liquid)
which distillation solvent is more effective?
when distilling with toluene, which layer does the water go to?
disadvantages of distillation methods
- difficult to read meniscus
- toluene can be a health/env hazard
- toluene is flammable
- not adaptable to routine, fast testing
- possibility of decomposing CHO or inducing Maillard rxns
what is the karl fischer method?
titration method - adaptable to products that show erratic results when heated or subjected to vacuum
can the KF method determine bound water?
when is the KF method used?
for low and very low moisture foods (dried veggies, spices, chocolate)
reagents in KF titration method?
- sulfur dioxide
supplied as 2 solutions
describe the KF titration
- Iodine and SO2 are added by a buret to the sample in a closed chamber
- excess I2 not reacted with water produces dark red-brown color
what's the role of iodine in the KF titration?
reacts with water. it gets converted to iodide.
what's the role of sulfur dioxide in KF titration?
produces sulfuric acid
what's the role of pyridine in KF titration?
acts as base
what's the role of methanol in KF titration?
what do you do if your food sample is solid but you wanna use KF titration?
- moisture must be made accessible by extracting with an appropriate solvent (methanol) after powdering the sample
- methanolic extract is used for titration
what compound is used as a primary standard during KF titration? why?
sodium tartrate dihydrate
it's very stable and contains 15.66% water under all lab conditions
true or false: particle size of sample is not an issue with KF titration
false - fineness of grind is important for penetration of solvent
true or false: atmospheric moisture is problematic during KF titration
true or false: moisture can adhere to glassware
true - equipment should be carefully dried prior to analysis
what food constituents can potentially interfere with KF titration?
- ascorbic acid: overestimate
- acetal formation releases water: overestimation
- unsaturated fatty acids react with iodine: overestimation
describe coulometric KF titration
- iodine is generated electrochemically during titration to titrate water in sample
- amount of I required to titrate is determined by current needed to generate iodine
which is more sensitive: volumetric or coulometric KF titration?
what are the physical methods of determining moisture?
- electrical method (measures conductance and capacitance)
what is conductance?
reciprocal of resistance (1/R)
what is capacitance
related to dielectric constant