ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: Shark 774 on April 07, 2011, 03:50:39 pm

Title: SPECTROSCOPY
Post by: Shark 774 on April 07, 2011, 03:50:39 pm

Hey guys, can someone give me a bit of a run down on the advantages and disadvantages between AAS, UV-Vis and Infrared? For examples: costs, accuracy, ease of use, etc. Would be greatly appreciated.

Thanks -

Title: Re: SPECTROSCOPY
Post by: Vincezor on April 07, 2011, 05:49:20 pm

AAS
Typical Uses: Analysis for metals/metalloids; e.g. Mercury in fish, Lead in soil samples, trace metals in mineral waters.

Advantages
- High sensitivity + Precision

Disadvantages
- Moderately Expensive
- Training required in order to operate

UV-Vis
Typical Uses: concentration of some coloured pharmaceuticals in blood serum, concentration of food colourings

Advantages
- Qualitative and Quantitative
- High Precision

Disadvantages
- Not suitable for substances with very low concentrations
- Limited to coloured solutions or compounds
- Equipment is expensive

Infrared
Typical Uses: Analysis of organic substances (measures covalent bonds)

Advantages
- Huge range of analytes/samples
- Only small sample size needed for analysis

Disadvantages
- Moderately expensive
- Requires training in order to operate

Title: Re: SPECTROSCOPY
Post by: scocliffe09 on April 10, 2011, 05:02:12 pm

Quote from: Vincezor on April 07, 2011, 05:49:20 pm

AAS
Typical Uses: Analysis for metals/metalloids; e.g. Mercury in fish, Lead in soil samples, trace metals in mineral waters.

Advantages
- High sensitivity + Precision - (these are two separate points) - can work at extremely low concentrations and is very accurate


Disadvantages
- Moderately Expensive
- Training required in order to operate
and only works for about 70 metal elements, for which you can get a HCL (hollow cathode lamp)

UV-Vis
Typical Uses: concentration of some coloured pharmaceuticals in blood serum, concentration of food colourings

Advantages
- Qualitative and Quantitative
- High Precision

Disadvantages
- Not suitable for substances with very low concentrations
- Limited to coloured solutions or compounds (I don't think this is correct - the whole point is that UV vis works in the UV spectrum too!!)
- Equipment is expensive

Infrared
Typical Uses: Analysis of organic substances (measures covalent bonds)

Advantages
- Huge range of analytes/samples
- Only small sample size needed for analysis

Disadvantages
- Moderately expensive
- Requires training in order to operate
- doesn't give 100% conclusive evidence about structure
- limited to organic compounds

Also - UV/Vis and AAS are both used to measure concentration via a set of standards, whereas IR is used to determine molecular structure. UV/Vis can be used to help determine the composition of a solution (qualitative) as well.

Title: Re: SPECTROSCOPY
Post by: Jdog on April 11, 2011, 03:08:23 pm

ive got a quick question, but i can't seem to find an answer to it anywhere!

in IR spec, why don't we get discrete lines, if the bonds in the molecule absorb specific quantas of energy in order to alter vibrational energy. Hieneman seemed to stress the point that the bonds absorb specific "discrete" energies but didn't explain why the peaks are broad.

and the same thign with Uv-VIs spec, however i think they don't absorb specific amounts because the enegry levels in molecules are altered when in aqueous form or molecular form

any help would be appreciated !