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principles of analytical chemistry > Newton 6 > Flashcards

Newton 6 Flashcards

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1
Q

How partition chromatography works?

A

Eluent and molecules are flowing through past the solid support, flowing in the gas phase. They will interact with the solid support, they will spend some time on the solid and liquid layer. And they will move back into gas (mobile phase)

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2
Q

What is eluent?

A

A fluid used to elute a substance.

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3
Q

How adsorption chromatography works?

A

There is no liquid layer on the solid surface. Molecules that are flowing past in the gas phase spend some time interacting with the surface and some time interacting with the gas.

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4
Q

What is gas-liquid chromatography?

A

It is based upon the partition of the analyte between a gaseous mobile phase and a liquid stationary phase that is immobilized on the surface of an inert solid.

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5
Q

Considering Gas Chromatography how do you choose gas phase?

A

Carrier gases must be inert (H2, He, N2)

Choice of gas is dictated by the type of detector employed, the nature of the stationary phase- separation, is it compatable with stationary phase, operation environment, cost of gas.

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6
Q

Considering gas chromatography how do you choose the sample?

A

Sample must me volatile, column efficiency requires that the sample must be introduced rapidly as a ‘plug’ of vapor. Slow injection of oversize causes band spreading and poor resulution.

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7
Q

What is used to introduce a sample to gas chromatography?

A

Sample is introduced as solution using microsyringe. Typical injection volume 0.1-1 μL

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8
Q

What is teh primary role of injector?

A

It is to volatilize the sample and introduce the appropiate quantity of the sample vapour onto the analytical column.

The temperature of the injector block is held constant - approximately 50oC higher than bp of the least volatile component.

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9
Q

Waht is the purpose of sample splitter (1:100 to 1:500) in capillary column?

A

It reduces volume of vapour imtroduced onto column.

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10
Q

What is autosampler?

A

It is a robot that injects the sample in precise and controlled quantities. It reduces error.

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11
Q

What is sampling valve?

A

It is 2 position valve that load/ inject the sample.

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12
Q

In general, what are two types of columns?

A

Packed and capillary

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13
Q

How is this capillary column called?

A

Wall coated open tubular coated

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14
Q

How is this capillary column called?

A

Support coated open tubular column

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15
Q

How is this capillary column called?

A

Fused silica open tubular column.

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16
Q

What is column tempearature and how it is maintained?

A

Column temperature equal to, or slightly above the boiling point of the sample will result in reasonable elution times (2-30 mins).

Generally, the temperature of the column is maintained by placing it in thermostatically controlled oven (air bath).

17
Q

What is advantage of temperature programming?

A

It can improve both resolution and reduce overall analysis time.

18
Q

How to achieve optimum resolution?

A

It is achieved at lower temperatures, however separation increases with column length (elution time) but so does peak width, zone broadening.

19
Q

What are ideal characteristics of detectors?

A

Highly sensitive,

stable and reproducible,

linear responce to analytes over large range of concentrations,

operating range from room temperature to 400oC,

a rapid responce to analytes that is independent of flow rate,

reliable and easu to use,

similar in responce to all samples or highly predictable and selective towards one or more types of sample,

nondestructive to the sample

20
Q

What are applicable samples of flame ionization detectors?

A

Hydrocarbons

21
Q

What are applicable samples of thermal conductivity detectors?

A

Universal detector

22
Q

What are applicable samples of mass spectrometer detector?

A

It is tunable for any species.

23
Q

What is typical detection limit for flame ionization detector?

A

0.2 pg/s

24
Q

What is typical detection limit for thermal conductivity detector?

A

500 pg/mL

25
Q

What is typical detection limit for mass spectrometer detector?

A

0.25-100 pg

26
Q

What thermal conductivity detector (TCD) measures?

A

Changes in the thermal conductivity of the eluent mixture as it flows through the cell.

27
Q

Why using TCD we low concentrations of analyte can be detected?

A

The thermal conductivity of carrier gases (H2, He) is roughly 6-10 times greater than that of a typical organic.

28
Q

Why for TCD twin detectors are normally used?

A

One is used as a reference for the carrier in the absence of analyte.

29
Q

What concentration sensitive means?

A

That the peak areas on a chromatogram will increase as flow rate decreases. Because it means that if your eluent is in contact with detector for longer you get a stronger responce.

30
Q

What is flame ionisatu=ion detector and how it works?

A

The FID is essentially a flame that burns the analyte as it elutes, ions generated in the flame are detected by monitoring the current between the grounded jet and a charged collector plate.

31
Q

What information FID produces?

A

Number of ions produced and it is proportional to the number of reduced C atoms in the flame.

32
Q

To what FID responds?

A

To number of C atoms entering the detector per unit of time. Flow rate does not matter.

33
Q

Why FID is mass sensitive?

A

Because it responds to the number of C atoms not flow rate.

34
Q

Why FID do not respond to H2O, CO2, SO2, NOX?

A

Because they are not flamable, they are in their higher oxidation state.

35
Q

What can be done to FID so it would detect CO and CO2?

A

FID can be connected to methanizers that converts non flamable gases to flamable

36
Q

When Ni catalyst used in FID as methanizers how does CO and CO2 react?

A

CH4 can be easily detected

37
Q

How do you calibrate a detector?

A

Samples of known concentration are prepared and multiple analyses are carried out on each solution. Calibration curve is ploted and using linear reagion we can find a concentration of the unknown.

principles of analytical chemistry (11 decks)

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