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Food Chem Midterm #2
Terms in this set (42)
What does the acronym SPE stand for?
Solid phase extraction
An HPLC system consists of what parts?
Injector, pump, solvent reservoir, column, detector.
Which type of HPLC separation was used in the caffeine analysis?
In order to work quantitatively what aspects in an analytical method need to known/determined?
all of the above
What type of inonization was used in the Saturn 2000 (the MS you used) for the GC-MS lab on caraway volatiles?
Electron Impact Ionization (EI)
The mass spectrometer does what?
All of the above
What is the separation method for the ionized mass fragments that the Saturn 2000 uses?
Why are the thermal desorption unit and transfer lines all held at 250 degree C in a GC-MS method such as the one used to determine caraway seed volatiles?
To prevent condensation of volatiles
The Biuret method for protein determination is based on the reaction/complex formation of the copper reagent with the
amines in the peptide bond
In order for the Biuret method to work, the protein/peptide has to be at least a
Of the three protein methods, Kjeldahl, Biuret, and Bradford, which one has the best detection limit?
The quantitation of the protein in the biuret method is done by using
an external standard curve.
In the biuret method the sodium potassium tartrate is used to
keep the copper-protein complex in solution.
In the Kjeldahl method, the nitrogen is transferred into boric acid for titration. What exactly is being titrated?
The borate ions that are formed during the transfer
In the Kjeldahl method the first step is the digestion off the sample. The step involves:
The digestion of the sample with a strong acid (sulfuric acid), Breakdown of all the proteins, and the conversion of all nitrogen into ammoniumsulfate
In the Kjeldahl neutralization step, not only is the acid, which was used to digest the sample, neutralized, but the nitrogen is also released in the form of
The Kjeldahl method for protein is called a "crude protein analysis" because
it measures all the nitrogen
In the Kjeldahl method the nitrogen is transferred from the original digestion flask to the boric acid "recepticle" by
Of the three protein methods, Kjeldahl, Biuret and Bradford, which one has the best detection limit?
The Bradford method uses which dye?
Coomassie Brilliant Blue
The Bradford method for protein determination is based on the reaction/complex formation of the dye with the
Protein due to ionic interactions.
The quanititation in the Bradford method is done by using
an external curve
What type of ionization was used in the Saturn 2000 for the GC-MS lab on caraway seed volatiles?
Electron Impact Ionization (EI)
The acronym SPME stands for
Solid Phase Micro Extraction
Why are the thermal desorption unit and transfer lines all held at 250°C in a GC-MS method such as the one used to determine caraway seed volatiles?
to prevent condensation of volatiles.
In SPME extractions, increasing the temperature of the sample vial has what effect?
It changes the equilibrium for a volatile chemical so that less of the chemical goes from the headspace onto the fiber.
In headspace extractions, increasing the temperature of the sample has what effect?
It changes the equilibrium for a volatile chemical so that more of the chemical goes into the headspace.
What are the 3 requirements for the internal standard?
1. Must not be naturally present 2. Must chemically behave like the chemical of interest 3. Peak must be separate from other peaks
What is the retention index?
The retention time for hydrocarbons (hexane, nonane, etc.) multiplied by 100.
What is the difference between static and dynamic headspace analysis?
Static: Sample and headspace come to an equilibrium. Dynamic: a carrier gas flows through the sample chamber.
Enzyme efficiency increases with ___ of the Michaelis constant
The michaelis constant in the Lineweaver Burke plot is
the negative inverse of the x-axis intercept
The Lineweaver Burke Plot shows
the inverse substrate concentration versus the inverse velocity
The maximum velocity in the Lineweaver Burke plot is
the inverse of the y-axis intercept
The Michaelis constant
is the substrate concentration at half maximum enzyme velocity.
The velocity of an enzyme-catalyzed reaction is
linearly related to enzyme concentration.
Mobile phase stays the same throughout the run
Use multiple mobile phases. This changes the retention times.
What is the GC equivalent to an isocratic system?
Isothermal- the temperature stays the same.
= highest point of peak - lowest point of peak
= (peak height)(Length of peak base)
HPLC vs. GC
HPLC- slow, a good run separate about 20 chem/hour column like a packed column. GC- Fast, separate about 100 chem/hour, people make non-volatiles into volatiles in order to use GC over HPLC.
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