Instrumental Analysis

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Astronomical spectroscopy

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Instrumental Analysis

AES

Generally low-viscosity soln.

Moderately expensive instrument

Flame test

light emitted through split

through prism

E-spectrum

Flame atomises metals. (converts ions -> atoms)

Each element is unique

dist. of electrons from nucleus

diff no of protons in nucleus

no. of occupied shells can be diff.

AAS

Analyte needs to be metals

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

Each element has a unique absorption spectrum

Elements analysed need own light source that emits the correct wavelength

Called a hallow cathode lamp

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

Extremely sensitive

Very versatile, able to detect over 70 elements

Most of widely used of modern instrumental techniques

UV-Vis Spectroscopy

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

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

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

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

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

NMR Spectroscopy

Very expensive to buy & operate

Has to be organic molecules

Carbon-13 NMR

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

Area under the peak = ratio of C13 enviro

num of peaks = num of C13 enviro

H1 NMR

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

Peaks are split by the n+1 rule

This shows the number of protons the hydrogen is adjacent to

Area under peak = ratio of Hydrogen enviro

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

num of peaks = num of H enviro.

Identifies the structure of molecules using radio waves

Infrared Spectroscopy

- Moderately expensive - Requires a trained technician

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

Most useful for qualitative analysis

Fingerprint or elucidation of structure

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

Diff. bonds will absorb diff. wavelengths of infrared

Each peak represents a bond

Can identify the bond through the use of the data booklet

Chromatography

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

It is the separation of mixtures

TLC

Uses Retention Factor (Rf)

Poor precision & accuracy

Cheapest method of chromatography

Spots visible if coloured or under UV light

Concentrated solution is applied at base rises by capillary action

Gas Chromatography

Sample must be easily converted into a gaseous form

Sample must be volatilized without breaking down

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

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

Detected by heat absorption and retention time is recorded

HPLC

LIMITATIONS

Sample must be soluble in the solvent

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

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

Components detected by UV

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