Instrumental Analysis

Chromatography

HPLC

Sensitive type of analysis.
i.e, Used to check purity of drugs.

Components detected
by UV

Mobile phase is a liquid.
i.e, could be water+ethanol

Best to use Medium to High Molecular Mass Organic compounds as analytes

LIMITATIONS

Sample must be soluble in the solvent

Gas Chromatography

Detected by heat absorption
and retention time is recorded

Most Sensitive type of chromatography.
i.e, Able to detect as little as 10^-12g

Mobile Phase is an inert gas.
i.e, Nitrogen

LIMITATIONS

Sample must be volatilized
without breaking down

Sample must be easily converted
into a gaseous form

TLC

Concentrated solution is applied
at base rises by capillary action

Spots visible if coloured or
under UV light

Cheapest method of chromatography

LIMITATIONS

Poor precision & accuracy

Uses Retention Factor (Rf)

It is the separation of mixtures

based on the principle of different rates of adsorption and desorbption to and from mobile and stationary phase

Infrared Spectroscopy

Each peak represents a bond

Can identify the bond through
the use of the data booklet

Can be detected due to the bonds in the molecule absorbing the infrared

Diff. bonds will absorb diff.
wavelengths of infrared

Most useful for qualitative analysis

Fingerprint or elucidation of structure

LIMITATIONS

Analyte has to be of organic molecules.
i.e, ethanol

- Moderately expensive
- Requires a trained technician

NMR Spectroscopy

H1 NMR

Identifies the structure of
molecules using radio waves

num of peaks = num of H enviro.

Chemical shifts are measured
relative to (TMS).
i.e, the furthest peak on the right

Area under peak = ratio of Hydrogen enviro

Peaks are split by the n+1 rule

This shows the number of protons
the hydrogen is adjacent to

When an external
magnetic field is applied to the protons spin state, they align either
against (high energy) or with (low energy) the field.

The can move between energy levels by emitting or absorbing radio waves

Thus protons in diff. enviro
absorb different frequencies

Carbon-13 NMR

num of peaks = num of C13 enviro

Area under the peak = ratio of C13 enviro

n+1 rule shows the num.
of Carbon the actualy carbon is adjacent to

LIMITATIONS

Has to be organic molecules

Very expensive to buy & operate

UV-Vis Spectroscopy

Arise when photons have enough energy
to move electrons from low energy to high energy level

Mainly used for determining the []
of a substance in sample

Have to select specific wavelength
which strongly absorbs the comp. but not other comp. in sample

i.e, determining the level of nutrients
in water and foods

LIMITATIONS

Low molecular mass & and it
has to be an organic molecule

AAS

Most of widely used of modern
instrumental techniques

Very versatile, able to
detect over 70 elements

Extremely sensitive

Usually measures [] of elements.
i.e, [] of mercury in fish

Each element has a unique absorption spectrum

Elements analysed need own light
source that emits the correct wavelength

Called a hallow cathode lamp

Sample is sprayed into flame

Atoms being analysed that are present in the flame absorb some radiation

Amount of light absorbed indicates the quantity of the element in the original sample

LIMITATIONS

Analyte needs to be metals

AES

Each element is unique

no. of occupied shells can be diff.

diff no of protons in nucleus

dist. of electrons from nucleus

Flame test

light emitted through split

through prism

E-spectrum

Flame atomises metals.
(converts ions -> atoms)

LIMITATIONS

Analyte needs to be metals

Moderately expensive instrument

Generally low-viscosity soln.