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Analytical > Analytical Session 1 > Flashcards

Analytical Session 1 Flashcards

1
Q

Chromatography

A

Method of separating a mixture between two phases. Used for quantitative and qualitative analysis

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2
Q

To achieve separation

A

the analytes need to spend different lengths of time being retained by the stationary phase

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3
Q

Mode

A

How the analytes interact with stationary phase

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4
Q

What are the modes of separation?

A

the four modes: adsorption,partition, ion exchange, and size exclusion.

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5
Q

Chromatogram

A

a graph showing separating the components of a mixture by chromatography.

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6
Q

A good chromatogram will have:

A

All analytes separated
Well separated peaks
Symmetrical, sharp peaks
Short run times

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7
Q

normal phase chromatography

A

has a polar stationary phase (eg silica gel) and a non-polar mobile phase (eg hexane)

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8
Q

reverse phase chromatography

A

has a non-polar stationary phase and a polar mobile phase.

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9
Q

In thin-layer chromatography, the retention factor (Rf) is used

A

to compare and identify compounds.

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10
Q

The solvent system that gives the best resolution during TLC

A

can also be used to purify the compound using column chromatography

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11
Q

Phase

A

a distinct and homogeneous form of matter (i.e. a particular solid, liquid, or gas)

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12
Q

Analytes

A

a substance whose chemical properties are being identified and measured.

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13
Q

Sample binds to stationary phase bearing strong negative charges, and dissolves in mobile phase with high electrolyte concentration

A

Ion exchange chromatography

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14
Q

Sample equilibrates between a liquid trapped inside porous particles and mobile liquid outside the particles

A

size exclusion chromatography

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15
Q

Sample equilibrates between liquid bound tightly to stationary phase particles and a mobile phase

A

: partition chromatography eg gas chromatography (based on polarities)

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16
Q

The mode used in TLC

A

adsorption chromatography (based on polarities)

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17
Q

An ion exchange chromatography, what are the forces involved?

A

Electrostatic forces

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18
Q

absorption chromatography, what are the forces involved?

A

VanderWaal forces are involved. Polar interactions from dipole dipole forces and hydrogen bonding.

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19
Q

In adsorption chromatography a very nonpolar mobile phase as used

A

FALSE The mobile phase can be polar or nonpolar in absorption chromatography

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20
Q

In reversed-phase chromatography, the mobile phase is more polar than the stationary phase.

A

TRUE In normal phase chromatography the mobile phase is less popular than the stationary phase

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21
Q

In partition chromatography the stationary phase is a solid

A

FALSE In gas chromatography The stationary phase is a liquid

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22
Q

A cation exchange resin binda and exchanges positive ions

A

TRUE Once the positive ions have bound to the cation exchange resin, the mobile phase can be changed and the bound ions will be released

23
Q

Chromatography is a technique for the SEPARATION of a mixture, in which the sample is introduced into a system of two different PHASES.One of the latter is continually being added to the system and is called the MOBILE PHASE. Differences in ADSORPTION/PARTITIONS/ INTERACTIONS shown by the sample components due to their structures and properties cause them to travel at different speeds.

A

analysis, separation, determination, substances, chemicals, phases, adsorption, distribution, partition, liquid, mobile phase, system, narrowness of peaks or bands, degree of peak or band separation]

24
Q

Adsorption chromatography:
Stationary phase
Mobile phase
Interaction
Diagram
Uses

A

Solid eg silica gel
Liquid eg petroleum ether and acetone
Polarity VdV
TLC/ HPLC

25
Q

Normal and reverse phase applies to both

A

Adsorption (TLC) and Partition (GLC)

26
Q

Diagram of adsorption

A

See “analytical”

27
Q

Adsorption chromatography forces

A

Hydrogen bonding (VdV interactions)

28
Q

Polarity of silica

A

Has an OH group, makes the overall molecule polar

29
Q

Which is the non polar phase in reverse phase

A

The sp is non polar eg C18 and the mp is polar eg methanol and water

30
Q

In reverse phase chromatography of a non-polar sample, will increasing the polarity of the mobile phase cause the retention time to rise or fall?

A

In reverse phase the sp in non polar eg c18, making the mobile phase less like the sample will increase retention times

31
Q

Describe the important functional differences between both the stationary phase and the interactions leading to sample binding and separation, in the four cases of adsorption, partition, ion exchange and size exclusion chromatography.

A

Table

32
Q

Name the four principal classes of chromatography based on the interaction of components with the stationary phase. In each case, describe the type of interaction that results in retention of components, and also the basis for separation of different components.

A

Table

33
Q

What modes can use normal and reverse phase chromatography

A

Partition and adsorption

34
Q

Principles of size exclusion chromatography

A

mp continuously added.
Smaller molecule elute quicker (stick in a forest)

35
Q

Liquid liquid extraction

A

Pre analytical testing to prepare for analysis to isolate components in sample

Based on differential solvent

eg spinach pigments in a solvents add another immiscible solvent when they are put together they created two layers when slightly agitated. Can decant sample and solvent of interest

36
Q

What happens when 100% Hexane:0% Ethyl Acetate is used as the solvent?

A

The components remain on the baseline.

37
Q

The solvent in TLC is also known as the

A

Mobile phase

38
Q

Good separation occurs when rf

A

<1

39
Q

Retardation factor is the ratio of

A

Distance moved by substance from base line to distance moved by the solvent from base line

40
Q

In TLC, initially the sample is

A

Not in contact with mobile phase

41
Q

True or False: Hexane is more polar than Ethvl Acetate.

A

False

42
Q

In TLC, you allow the solvent to travel

A

To nearly the top of the plate.

43
Q

Atomic absorption spectrometry v AES

A

AAS
Energy and wavelengths absorbed by atoms

AES
Energy and wavelengths emitted by excited electrons

44
Q

What happens during when a sample absorbs radiation

A

When a sample is exposed to light energy that matches the energy difference between two levels, the electrons will be excited and the electrons will be promoted to the higher orbital. Energy is absorbed by the sample and a spectrometer records the degree of absorption at different wavelengths and the results are plotted, absorbance (A) versus wavelength
this is known as a spectrum.

45
Q

Lambda max

A

the wavelength at which there is a maximum adsorption
Example - Isoprene
The absorbance at 222 nm is due to excitation of electrons from pi to pi star

46
Q

Absorption coefficient

A

It is simply the absorption of light at a particular wavelength by a 1 mol/litre solution with a 1 cm light path. It is the factor a or ε seen in the Beer Lambert equation.

47
Q

Hplc experiment

A

In GLC, the two phases are Gas and Liquid. In HPLC, the phases are both liquid. Both can be changed to improve resolution and define the optimal conditions for separation. In this experiment Reverse Phase HPLC will be used. The mobile liquid (phase) is a polar mixture of 70 % methanol and 30 % water. The stationary phase is a non-polar long-chain alkane, octadecylsilane C18H38, which is bonded to the silicon beads which fill the column. Partition of the sample occurs between the mobile and stationary phases, depending on the polarity of its constituents.

48
Q

Internal standard practical

A

For your lab, a series of standards is prepared, having varying concentrations of Ethanol (Alcohol), but each having the same concentration (10%) of Propanol. Each of these is used to obtain a chromatogram, from which the ratio
Peak area Ethanol
Peak area Propanol
is obtained. A standard curve is drawn of this peak area ratio versus Ethanol
concentration.
Samples are also spiked with 10% Propanol, and the peak area ratio is obtained for each. This ratio can be used to obtain the % Ethanol from the standard curve. The Ethanol concentration of the actual samples can then be found by adjusting for the Propanol dilution and any other dilutions carried out.

49
Q

Beer lambert experiment

A

This experiment (and absorption spectroscopy in general) derives from the fact that most molecules will absorb electromagnetic radiation (visible and invisible ‘light’). Different compounds vary in the extent to which they absorb electromagnetic radiation and the wavelengths which they absorb. This experiment demonstrates these two points.
Theory

A=εcl
A = Absorbance
ε = Molar absorption coefficient (which reflects the extent of absorption by individual molecules in the solution)
l = Light path length through the solution
c = Concentration of test solution

The Beer-Lambert Law states that when light is shone through a solution, the amount of light absorbed depends on the nature of the molecules in the solution, the length of the light path through the solution and the solution concentration where:

Absorbance is directly proportional to
Concentration (A  C), since in any experiment ε and l are constant.

50
Q

Beer lambert experiment 2

A

This experiment concerns the ability of different molecules to absorb radiation (in this case visible light) to different extents at different wavelengths. A visual (graphical) display of this absorption pattern is called an absorption spectrum.

Tabulate your results. Plot a graph with all your results using Excel, absorbance on the vertical axis and wavelength on the horizontal axis.
This video shows how to create a graph (spectrum) of absorbance versus wavelength.
These graphs are called spectra, and the differences in complexity are due to differences in molecular structure of the two compounds. Find a published spectrum for carotene in a book or on the net for your report, and discuss yours and the published version

While the compounds used above absorb visible light (which is why they are coloured), in practice more compounds absorb ultraviolet light, or uv as well as visible light.

the very significant difference in double bond arrangement that gives rise to the differences in spectra. Include the spectra/observations in your report.

This experiment illustrates the fact that absorption intensity and spectrum are critically dependent on molecular structure.

51
Q

Session 8. Determination of Fe in Cu-Ni alloy by Atomic Absorption Spectrophotometry

A

A standard source of radiation, consisting of the atomic spectrum of Iron, is passed through a solution of Iron, which is atomised in an oxy-acetylene flame. Some of this radiation is absorbed by some of the Iron in the flame. This Absorbance obeys the Beer-Lambert Law.
We prepare standard solutions of known concentrations, obtain a standard curve from their Absorbances, and use this to find the Concentration corresponding to the Absorbance of a sample solution.

52
Q

Session 9. Standard Addition Method in AAS to determine the Fe content of a Cu-Ni Alloy

A

Prepare the sample so it has a concentration of approximately 4 ppm Fe. Measure its Absorbance, and then add increasing amounts of standard Fe solution to the sample, measuring Absorbance after each addition. Plot the results on a Gran’s Plot. The concentration of Fe in the sample will be indicated by the point where the line crosses the x-axis as in the example below:

53
Q

Session 3. Use of Gas Liquid Chromatography to:

A

1) Identify the number of components in a mixture of homologous alcohols
2) Identify each individual component
3) Determine the percentage composition of the mixture
Chromatography is based on the principle that different molecules interact to a different extent with different kinds of substances. This fact can be used to separate mixtures of various substances.
In GLC, the two phases are Gas (mobile phase) and Liquid (stationary pahse). In GLC chromatography, the stationary phase is generally a non- volatile liquid, which coats an inactive, pulverized, solid material packed within a very long (30 meters) thin (1/4 of a millionth of a meter) column. The mobile phase is generally an inert gas such as Nitrogen or Helium and is referred to as a carrier gas. Our gaseous phase is Helium.
The components of the mixture to be separated must be volatile. A very small amount of solution (perhaps 6/10 of one millionth of a liter) is injected into the injection port of the chromatography system using a syringe. The mixture is immediately vaporized and carried by the carrier gas into the column. The column, like the injection port and the detector, is kept at a controlled temperature inside an oven so that the mixture remains in vapour form. From the time the materials are injected into the instrument until they reach the detector, they are being retained by the liquid in the column (the stationary phase).
The time each substance is retained is called its retention time and is usually represented in minutes. Experimental conditions (for example, temperature and choice of column) are chosen so that each component of the mixture has a different retention time and, therefore, reaches the detector separately and appears as a peak on a chromatogram. There are several types of detectors, but the one used in this experiment is a flame ionization detector. This detector essentially counts carbon atoms, and therefore, the area under each peak represents the amount of component in the mixture. Thus, both qualitative and quantitative information can be gathered.

54
Q

Liquid liquid

WAPE

A

The lower phase is largely water and acetone, and the.

upper the petroleum ether since it has low density. Run off the lower phase into the original conical flask for discarding and collect the upper phase in a clean container

Analytical (9 decks)

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