topic 15E

separate components of a mixture based on their attraction to the mobile phase and the stationary phase.

solvent (liquid or gas) that carries the components of the mixture through or over the stationary phase.

Components that are more attracted to the mobile phase move faster and further.

the stationary phase is the solid or liquid supported on a solid surface that stays fixed in place.

Components that are more attracted to the stationary phase move slower.

: Separation happens because different substances have different affinities for the mobile and stationary phases.

A substance that spends more time in the mobile phase moves further.

A substance that spends more time in the stationary phase moves less.

To prevent the mixture from dissolving directly into the solvent, ensuring it travels up the paper or plate

Because the solute can never move further than the solvent front — it travels with the solvent, not beyond it.

The substance is more soluble in the mobile phase.

It moves further up the plate/paper.

It has weaker attraction to the stationary phase.

The substance is less soluble in the mobile phase.

It has stronger attraction to the stationary phase.

It moves shorter distance.

depends on experimental conditions such as:

Type of solvent used (polarity).

Temperature.

Type of stationary phase (paper vs silica).

Thickness of the TLC layer.

Column chromatography separates substances based on their different retention times as they pass through a column containing the stationary phase.

he retention time is the time a substance takes to travel through the column and reach the detector.

It depends on how strongly the substance interacts with the stationary phase and how volatile or soluble it is in the mobile phase.

Stationary phase: solid or liquid on a solid inside the column.

Mobile phase: liquid solvent pumped at high pressure through the column.

Stationary phase: liquid or solid coated on the inside of a long capillary column.

Mobile phase: inert carrier gas (e.g., helium or nitrogen).

Substances are separated because they spend different amounts of ti

HPLC or GC separates the mixture into individual components based on their retention times.

Then, mass spectrometry identifies each component by measuring its mass-to-charge ratio (m/z) and producing a mass spectrum unique to each substance.

Forensic analysis (identifying drugs, toxins, explosives).

Drug testing in sport (detecting banned substances).

Environmental analysis (pollutant detection).

Pharmaceuticals (purity and composition testing).

difficult to control all the variables
different substances may have the same retention times
a reference(data-book) is needed to identify the substance

Y-axis: Absorption (signal intensity)

X-axis: Chemical shift (δ) in ppm (parts per million)

CDCl₃ (deuterated chloroform)

D = deuterium, a heavy isotope of hydrogen

TMS (Tetramethylsilane)

Its signal is used as a zero point for chemical shifts.

All other carbon signals are measured relative to TMS.

Chemically inert (doesn’t react with the sample)

Gives a single sharp signal (all carbons equivalent)

Volatile (easily removed from the sample)

CH₃: one environment → 1 peak

CH₂: one environment → 1 peak

Because they are chemically equivalent,

Example: CH₃ groups in CH₃CH₂CH₃ (the two CH₃ carbons are in different environments, so different peaks).