Lecture 13 - Minerals Flashcards
what are the major components of food?
water, ash, lipids, carb, proteins, dietary, fibers
what are the minor components of food?
minerals, vitamins, organic acids, enzymes and alcohol, nutraceuticals
define minerals
inorganic species or substances of neither animal or plant origin (doesn’t contain C, H, O or N skeleton)
why do we analyze for mineral content?
- nutrition
- food safety
- food fraud
- government regulations
- food processing (fortification, preservative)
requirement for macrominerals?
more than 100 mg per day
requirement for trace minerals?
milli or microgram quantities per day
what are some macrominerals?
calcium, phosphorus, sodium, potassium, magnesium, chlorine, sulfur
what are some trace minerals
iron, iodine, zinc, copper, chromium, manganese, molybdenum, fluoride, selenium, silica
requirement for ultra trace minerals
still under research
heavy metal definition?
toxic to the body
what are some ultra trace minerals
vanadium, tin, nickel, arsenic, boron
what are some heavy metals?
lead, mercury, cadmium, arsenic
what 5 methods do we have available for food minerals?
1) potentiometry using ISEs
2) anodic stripping voltammetry (ASV)
3) titrimetry (EDTA complexometric and precipitation titration)
4) colorimetric
5) instrumental (atomic absorption, atomic emission)
what method can you use to test for hardness of water?
- EDTA complexometric titration
describe the EDTA complexometric titration method
- EDTA forms 1:1 complexes with numerous minerals
- end points are detected using mineral chelators that have coordination constants lower than EDTA
- different colors are produced in each of their complexed and free states
what indicators are used for the EDTA complexometric method? (used for Ca or Mg)
- calmagite
- eriochrome black T (EBT)
describe the color changes that happen with calmagite
Ca or Mg reacts with a few drops of Calmagite under basic pH (ammonia buffer makes pH 10) and turns pink
the pink complex is then titrated with EDTA complex to make a blue complex
what’s the point of the ammonia buffer in the calmagite thing for EDTA complexometric titration
- maintain basic pH
- improve stability of EDTA-metal ion complex
- improves sharpness of endpoint
- makes sure pH doesn’t exceed 11 or else Ca and Mg would precipitate as hydroxides
what is precipitation titration?
when at least one product of a titration reaction is an insoluble precipitate, it is referred to as precipitation titrimetry
what methods of precipitation are there?
- Mohr method
- Volhard method
describe the Mohr method
- determines Cl
- AgNO3 reacts with Cl ions to make AgCl and NaNO3 until all Cl- ions are complexed
- Ag reacts with K2CrO4 to make Ag2CrO4, which is orange
describe the volhard method
mostly used for determining salt in high salt products
- sample added with excess AgNO3
- AgCl is precipitated out
- moles of AgNO3 is left behind in the supernatant solution is measured by:
- sample is wet ashed with HNO3
- excess AgNO3 is back titrated with KSCN; ferric ammonium sulfate
- end point forms a salmon-pink (ferric thiocyanate)
what happens if you add HNO3 before adding AgNO3? (volhard method)
get loss of chloride by volatilization
what are some of the chromogens used for colorimetric methods?
- Alizarin 3-sulphonate for Ca determination
- 0-cresolphthalein for Ca (under alkaline pH)
- Ferrozine and Ferene-S for Iron
- o-phenanthroline for Iron in meat
how can you determine iron in meat colorimetrically ?
react ferrous iron with o-phenanthroline to form orange-red complex ion
describe atomic absorption sepctroscopy
quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state
ground state to excited
what atomic absorption spectroscopy methods are there? which one of them is the most sensitive?
- flame atomic absorption spectroscopy (FAAS)
- graphite furnace atomic absorption spectroscopy (GFAAS)
- cold vapor atomic absorption spectroscopy (CVAAS)
GFAAS
describe atomic emission spectroscopy
based on the measurement of the electromagnetic radiation absorbed or emitted by the atoms of the measured element in a sample
excited to ground state
what atomic emission methods are there?
- flame atomic emission spectroscopy (FAES)
- inductively coupled plasma atomic emission spectroscopy (ICP-AES)
- inductively coupled plasma optical emission spectroscopy (ICP-OES)
atomic spectroscopy requires that _____ of the element of interest be in the _____ state and that they be well separated in space
atoms, atomic
in food, elements are present as _____ or _____
compounds or complexes
so they must be converted to neutral atoms before atomic absorption or emission measurements can be made
what is atomization?
separating particles into individual molecules and breaking molecules into atoms
how is atomization accomplished?
high temperatures in a flame or plasma
