Final Study Guide Questions Flashcards
(30 cards)
Define HPLC and UPLC. What is their difference?
HPLC: high pressure liquid chromatography
UPLC: ultra high pressure liquid chromatography
The main difference is because the pressure is higher during UPLC the particles can be smaller leading to better separation.
What kind of compounds elute first from the column in normal and reverse phase HPLC? Why?
Normal phase: stationary polar phase and mobile non polar phase so non polar analytes elute more quickly
Reverse phase: stationary non polar phase and mobile polar phase so polar analytes elute more quickly
It all depends on the affinity between the stationary phase and the analyte. If they have a high attraction it will take longer to elute
Why do you need to degas the HPLC solvent?
Degassing prevents bubbles from forming which would ruin separation, break up flow, and change the pressure - all of which will skew results
How can you determine orange juice is adulterated with grape juice?
To determine adulteration, spike the orange juice with compounds known to be in grape juice such as anthocyanins. Then conduct HPLC on both of them. If the peaks are the same at the anthocyanin region the orange juice was adulterated
How do grapefruit compounds promote bioavailability of certain drugs?
Grapefruit has a certain compound called beragamottin which when taking lipitor will cause lipitor concentration to increase along with its side effects. Beragamottin inhibits the detoxification enzymes from modifying the lipitor into a water soluble compound
How many ways are there to quantitatively evaluate the compounds eluting from the column? Which is better?
No detector is really better than the other - it all depends on the components that you’re looking for
There are five ways to quantitatively evaluate the compounds eluting from the column: PDA detector, fluorescence detector, emission detector, refractive index detector, and mass spectrophotometer
What is a PDA detector?
A PDA detector is a detector that can be connected to an HPLC or UPLC
Looks at how much light is absorbed by the compound
Good for measuring carotenoids
What is a mass spectrophotometer?
MS can be connected to an HPLC or UPLC
It ionizes the molecules by the addition of electrons and tells you the mass charge ratio and the fragmentation pattern
What is the difference between isocratic and gradient flow in HPLC?
Isocratic: slow elution, ratio of non polar to polar compounds in mobile phase remains constant
Gradient: rapid elution, the strength of the mobile phase increases to favor the molecules that elute first (two different mobile phases)
What are some advantages gas chromatography has over liquid chromatography?
GC requires a small sample with little preparation, it is good at separating complex mixtures, results are rapidly obtained, it is very precise, can detect volatile organic mixtures at low concentrations and the equipment is not very complex
What are some disadvantages of gas chromatography over liquid chromatography?
GC samples and mobile phases must be volatile and thermally stable
What are the three ways components are separated in GC?
Components are separated in GC by their boiling point, size of the compound, and the interaction with the stationary phase
What are the main components of a GC?
Gas –> flow control –> injector port –> column (in oven) –> detector –> recorder
What are some food applications for GC?
Food applications: triglycerides, cholesterol, aromatics, volatile oxidation products, ethanol, and antioxidants
What is the difference between the stationary phase in a capillary tube and a packed tube?
A capillary tube has a viscous liquid chemically bonded to the sides of the tube
A packed tube has a solid material bonded to the sides of the tube
Compare and contrast a packed tube and a capillary tube.
Packed: beads, porous layer, conventional, stainless steel/glass
Capillary: porous layer open tube, hollow fused silica glass, smaller diameter, longer column
What is an FID detector?
An FID detector is a flame ionization detector that is sometimes connected to a GC
Measures the ions formed during combustion of organic compounds in a hydrogen flame
What is the detection range of an FID?
The detection range is very broad and stretches 10^7 places
What are the three most common carrier gases used in GC? Compare and contrast them.
The three most common carrier gases used in GC are nitrogen, helium, and hydrogen. Nitrogen is the slowest but it is also safe and cheap. Helium is the most common and has the highest detector compatibility but it is becoming increasingly expensive. Hydrogen results in the quickest elution but it is also dangerous to use
What compound in citrus fruits is responsible for the aroma?
D-limonene is a volatile component found in fruits that is responsible for the aroma
When is split or split-less sample injection appropriate?
A sample must be split when there is too much analyte present or sample volume is too high (capillary).
A sample is split-less when there is a little amount of analyte in order to increase sensitivity
What are some examples of chemical modification or derivatization of food analytes?
Make thermally stable
make volatile
Change properties for better separation
When is chemical modification of analytes appropriate?
Chemical modification should be done when the compound is not thermally stable, not very volatile, or there is poor chromatographic separation due to polarity
What is mass spectrometry?
MS is a process of ionizing molecules, atoms, or molecular fragments and measuring the amount of electrons are produced
