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Food Analysis > Lecture 5 - Moisture Analysis 2 > Flashcards

Lecture 5 - Moisture Analysis 2 Flashcards

1
Q

2 parts of distillation methods?

A
  1. recovery of water by distillation

2. measurement of volume of water

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2
Q

steps in distillation

A

H2O is removed by distillation solvents –> vapour is cooled –> water is collected and measured

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3
Q

distillation solvents should be….

A

stable (chemically) at temp of distillation and free of water

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4
Q

2 versions of distillation solvents are

A
  1. immiscible and non volatile (ie mineral oil)

2. immiscible and volatile (toluene)

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5
Q

is the distillation method AOAC approved for moisture content analysis?

A

yes

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6
Q

is distillation direct or direct method of moisture determination?

A

direct

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7
Q

why is there less decomposition in distillation?

A

b/c there is faster heat transfer and water is removed quickly

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8
Q

what are the two distillation methods?

A
  1. direct

2. reflux

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9
Q

properties of mineral oil?

A

1-immiscible with water
2-non volatile
3-Boiling point 200-3100C
4-Density 0.8 g/ml.

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10
Q

properties of toluene

A 
1-immiscible with water
2-volatile 
3-Boiling point 110.60C 
4-Density  0.87 g/ml 
5-flammable.
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11
Q

differences and similarities between mineral oil and toluene?

A

similar: immiscible with water

diff:
min oil: non volatile
toluene: volatile and flammable

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12
Q

what is a important property of distillation solvents?

A

must be immiscible with water

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13
Q

why is it better to use volatile (toluene) than non volatile liquid?

A

distillation is more effective with volatile liquid

bp of toluene (110 degC) is fairly close to bp of water

both toluene and water will evaporate and be collected in receiving trap, but will not mix

water is heavier and will be the lower layer, thus volume can be measured directly

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14
Q

disadvantages of distillation methods?

A
  • meniscus layer is hard to read
  • toluene is aromatic hydrocarbon which is carbinogenic and an environmental hazard
  • solvents are flammable
  • not adaptable to routine testin
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15
Q

what method is used for chemical methods of moisture analysis?

why is it used?

A

the karl fisher method

  • adaptable to food products that show erratic results when heated or submitted to a vacuum
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16
Q

___ is a reactant in a chemical reaction

17
Q

advantages of chemical methods?

A
  • more specific for h2o than oven drying and distillation
  • fast (1-2 mins)
  • selective for water
  • accurate and precise
  • wide measuring range (ppm to %
18
Q

applications of chemical methods?

A

used in low moisture foods (ie dehydrated vegetables, spices and chocolate)

non food applications (ie cosmetics, plastics, fertilizers)

19
Q

what are chemical methods based on?

what solvents are needed?

A

reaction of bunsen

2H2O + SO2 + I2 H2SO4 + 2HI

needs non-aqueous solvents such as benzene, methanol and pyridine

20
Q

result of using benzene in the bunsen reaction?

chem methods

A

benzene can give erratic variable results because of incomplete reaction

21
Q

ratio of iodine : so2: pyridine in a methanol karl fisher solution

(chem methods)

22
Q

basic ingredients of KF reagents?

chem methods

A

iodine

sulfur dioxide (to produce sulphuric acid)

pyridine (base)

solvent: methanol

23
Q

to minimize losses of active reagent from side rxns that consume iodine, the reagent can be supplied as what two solutions? (chem methods)

A

solution of Iodine in methanol

sulfur dioxide in pyridine

24
Q

what does hydranal reagents use as a base instead of pyridine? (chem methods)

A

imidazole of diethanolamine

25
Q

what are accessories and reagents needed for chemical methods?

A

analytical balance

syringe to insert sample to bottle

karl fischer reagents

26
Q

what environment should KF instruments not be set up in?

A

areas subject to large temp fluctuations or high humidity

27
Q

can the KF reaction measure anything these besides water?

A

no, only water will be determined

28
Q

can KF titration determine bound water?

A

yes it can determine free and bound water

29
Q

steps for KF titration?

30
Q

types of KF titration?

A
  1. volumetric KF titration

2. Coulometric KF titration

31
Q

what do physical moisture analysis methods take advantage of?

A

physical properties of water

32
Q

examples of physical methods?

A

electrical

conductance (reciprocal of resistance 1/R)

capacitance (related to dielectric constant)

33
Q

electrical methods require ___ against samples of known moisture content as determined by standard methods

A

calibration

34
Q

what is infrared analysis

A

measures the absorption of infrared radiation by molecules in food

35
Q

what are other physical moisture analysis methods?

A
  1. infrared analysis
  2. nuclear magnetic resonance (NMR)
  3. chromatography techniques

Food Analysis (17 decks)

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