Lecture 11 - Mineral Content

Question 1

What are minerals?

Answer 1

inorganic species of substances that re neither animal or plant origin ( no CHON skeleton)

Question 2

What is the relevance of the minerals?

Answer 2

• nutrition
• food safety
• foo fraud
• government regulation
• food processing

Question 3

What does a lack fo iron, calcium and Na/K lead to?

Answer 3

Anemia, osteoperosis and heart failure

Question 4

What is the importance of minerals in food safety

Answer 4

products could be adulterated or comtaminated

ex. mercury

Question 5

What is the importance of food fraud

Answer 5

manufacturers can lie about what is in a food
ex vegetable vs. animal protein
soy–> silica present can be adulterated with sand

Question 6

What is the importance of minerals and government regulation?

Answer 6

Nutrition labelling form the FDR, needed for Na, Fe, Ca because of their importance with hypertension, anemia, impeding development

Question 7

What is the importance of food processing?

Answer 7

Food can be fortified to allow for the addition of nutrients that would be lacking naturally

ex. iodized salt
ex. breakfast cereals

Question 8

What are the 4 classifications?

Answer 8

Macrominerals
Trace minerals
Ultra trace minerals
Heavy metals

Question 9

What are some examples of Macro mienrals, trace minerals, ultrea trace minerals and heavy metals?

Answer 9

Macro >100mg/day –> Ca, P, Na, K, Mg, Cl, S
Trace mg-ug/day –> Fe, I, Z, Cu, Cr, Mn, Mb, F, Se, Si
Ultra trace minerals: do not have clear defined biochemical role
Heavy metals: toxic–> Pb, Hg, Cd, As

Question 10

What is Potentiometry using ion-selective electrodes (ISEs)?

Answer 10

Based on a sensor (transducer) that specifically bind to the dissolved ions to produce electrical potential

Question 11

What is Anodic stripping voltammetry?

Answer 11

involves (i) pre-concentration of a metal phase onto a solid electrode surface or into Hg (liquid) at negative potentials and (ii) selective oxidation of each metal phase species during an anodic potential sweep. Depending on the type of metal ions present, the current will change when increasing potential is applied to the electrode.

Question 12

What are the two methods of Titrimetry

Answer 12

EDTA complexometric titration

Precipitation titration

Question 13

What is the principle of the complexometric titration

Answer 13

Usually used for the hardness of water
The hexadentate ligand ethylenediaminetetraacetate(EDTA) forms stable 1:1 complexes with numerous mineral ions.
This gives complexometric titration using EDTA broad application in mineral analysis.
Endpoints are detected using mineral chelators that have coordination constants lower than EDTA (i.e., less affinity for mineral ions) and that produce different colors in each of their complexed and free states

Question 14

What indicators are used in the titrimetry test?

Answer 14

Calmagite and Eriochrome Black T (EBT) are such indicators that change from blue to pink when they complex with calcium or magnesium.
- The endpoint of a complexometric EDTA titration using either Calmagite or EBT as the indicator is detected as the color changes from pink to blue.
○ Sample with Ca or Mg + Calmagite (pH 10)—> Pink complex
○ Pink Complex +EDTA –> Blue complex

Question 15

What is the steps of the EDTA complexomteric titration?

Answer 15

Calmagite Indicator: ( Analysis of calcium and Magnesium in milk)
1-Prepare 0.036M EDTA solution.
2-Prepare ammonia buffer. Mix of ammonium hydroxide and ammonium chloride (pH 10-11).– Stability
3-In a 250ml Erlenmeyer flask add 50ml of milk, 3ml ammonia buffer (to make alkaline solution )and few drops of calmagiteindicator.
4-Titrated with EDTA solution.

Question 16

What causes stability in the calmagite indicator?

Answer 16

the ammonium chloride buffer

Question 17

What is the relevance of the ammonia buffer?

Answer 17

• To maintain pH of solution at pH10 ± 0.1.
Calcium and Mg will precipitate if the pH goes too high or too low
• Improve the stability of EDTA-Metal ion complex
• Improves the sharpness of endpoint
If the solution is not stable, you will not be able to find the endpoint
• Make sure pH does not exceed 11 as Ca and Mg will precipitate as hydroxides

Question 18

What are the two types of preciptation reactions

Answer 18

Mohr Method

Volard Method

Question 19

What is the principle of the precipitation titration?

Answer 19

When the least one product of a titration reaction is an isoluble precipitate, it is referred to as the precipitate

Question 20

What is the mohr method?

Answer 20

Chloride determination
Direct titration method
Based on the formation of orange- coloured solid silver chromate after silver from silver nitrate has complexed with all the available chloride

Question 21

What is the importance of water in the mohr method?

Answer 21

water is important to determine because it can interfere with:K2CrO4 reacts with water and might have some chloride that is present in solution

Question 22

What are the steps in the Mohr method? (chloride in butter)

Answer 22

1-Weigh about 5 g of butter into 250-ml Erlenmeyer flask and add 100 ml
of boiling H2O.
2-Let it stand for 5–10 min with occasional swirling.
3-Add 2 ml of a 5% solution of K2CrO4in H2O.
4 Titrate with 0.1 N AgNO3until having an orange-brown color.

Question 23

What is the principle of the Volhard method? (Cl determination)

Answer 23

volume of AgNO3 solution added must be in excess of that required to react with the chlorides in the sample

Question 24

What indicator is used in the Volhard method?

Answer 24

Ferric ammonium sulfate (FeNH4(SO4)2)is added as an indicator

Question 25

What are the steps of the Volhard method?

Answer 25

- back-titrate the excess AgNO3 with potassium thiocyante(KSCN) solution. - The FeNH4(SO4)2 reacts with an excess of thiocyanate (when all the Ag ions from AgNO3are used up), forming the salmon colored complex, ferric thiocyanate FeSCN++, indicating the end point.

Question 26

What are the reactions with the Volhard

Answer 26

``` Ag+ + Cl- -> AgCl (until all Cl- is complexed and is precipitated) Ag+ + SCN- -> AgSCN (to quantitate silver not complexed with chloride) SCN- + Fe3 -> [FeSCN]2+ (red when there is any SCN that is not complexed to Ag+ after all the Ag+ ions are depleted) --> back titration ```

Question 27

What is the principle of the Volhard reaction?

Answer 27

1. The sample is added with AgNO3 where AgCl is precipitated out and excess of AgNO3 remains. We are measuring moles of AgNO3 left behind in the subsequent steps 2. The sample is wet-ashed with HNO3 (to digest organic matter), 3. The excess AgNO3 is back titrated with Potassium thiocyanate (KSCN), using ferric ammonium sulfate as indicator

Question 28

What is the Volhard reaction used for?

Answer 28

determination of high salt content

Question 29

What is the flow chart of the Volhard reaction?

Answer 29

Sample + AgNO3--> AgCl + Excess AgNO3 + Organic compounds --> (wet ashing with hNO3)--> AgCl +Excess AgNO3--> FeNH4(SO4)2 *12H2O (indicator) --> Back titratio with KSCN--> Ferric thiocyanate (endpoint)

Question 30

What is the colorimetric method?

Answer 30

- Chromgens are chemical that upon reaction with the compounds of interest, form colored products - Chromogens are available that selctively react with a wide variety of minerals - Each chromogen reacts with its corrsponding mineral to produce a soluble colored product that can be quantified by absorption of light at specified wavelength

Question 31

How do you determine the iron content in meat?

Answer 31

- By reacting ferrous iron (Fe2+) with o-phenanthroline to form an orange-red complex ion according to the followring equation

Question 32

What are the instrumental methods for mineral determination?

Answer 32

Atomic absorption spectroscopy (AAS) | Atomic Emission

Question 33

What is atmic absorption spectroscopy?

Answer 33

- Can determine a lot of minerals form one test | - Atomic absorption spectra produced whe the ground state atoms or ions absorb energy froma radiation source

Question 34

What is Atomic Emission

Answer 34

- Atomic absorption spectra ar produced when ground state atoms absorb energy form a radiation source - Atomic emission spectra are produced when excited neutral atoms emit energy on returning to the ground state or a lower energy state

Question 35

What is atomization?

Answer 35

Atomization involves separating particles into individual molecules (vaporization) and breaking molecules into atoms. It is usually accomplished by exposing the analyte (the substance being measured) to high temperatures in a flame or plasma although other methods may be used.

Question 36

Absorption spectroscopy

Answer 36

atoms absorb light

Question 37

Emission spectroscopy

Answer 37

ions emit light (at very high temperature)

Question 38

What does Atomic spectroscopy require?

Answer 38

that atomsof the element of interest be in the atomic state (not combined with other elements in a compound) and that they be well separated in space. -In foods, virtually all elements are present as compounds or complexes and, therefore, must be converted to neutral atoms (atomized) before atomic absorption or emission measurements can be made.