Instrumental Analysis

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  • Created by: Jezebel
  • Created on: 15-05-13 09:03

Chromatography

Food scientist can ANALYSE different foods to see what ADDITIVES have been used. For example, food colourings can be detected by PAPER chromatography. They can use results from known compounds to positively IDENTIFY them.

  • Line drawn with pencil, and blobs of ink there.
  • Placed in a beaker of ethanol- because evaporates easily so raises the ink.
  • Not always accurate.
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Advanatges and Disadvantages of Instrumental Analy

ADVANTAGES:

  • many industries need RAPID and ACCURATE methods to analyse substances
  • HIGHLY ACCURATE
  • SENSITIVE
  • QUICKER
  • only SMALL samples are needed

DISADVANTAGES:

  • usually very EXPENSIVE
  • special TRAINING is required
  • results have to be compared to data from KNOWN substances- so new substances are hard to identify
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Gas Chromatography and Mass Spectrometry

GAS CHROMATOGRAPHY: (http://0.tqn.com/d/chemistry/1/0/Q/8/1/Gas_chromatograph.jpg)

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Gas Chromatography Steps

STEPS TO GAS CHROMATOGRAPHY:

  • Sample mixture VAPOURISED
  • 'Carrier' gas- CARRIES gas through coiled column
  • there is maetial in teh coil- comounds have DIFFERENT ATTRACTION to thsi material- either SLOWING/ SPEEDING up the time for gas to move
  • known as RETENTION TIME
  • compounds with WEAK attractions- SHORTER retention time
  • Compounds with STRONG attrctions- LONGER retention time
  • the different RENTION TIMES can be stored on: CHROMATOGRAPH
  • So the higher the peak on a chromatograph- MORE OF THAT COMPOUND IN THE SAMPLE
  • Peaks on the Chromatograph- compared to results of KNOWN substances---------------------------- BUT the known analysis MUST have taken place in the EXACTLY the same coditions to COMPARE rention times- to identify the substances.
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Mass Spectrometry:

  • To idenify UNKNOWN substances from the GAS CHROMATOGRAPHY- can be attatched to a MASS SPECTROMETER
  • identifies substances QUICKLY, ACCURATELY, and SMALL QUANTITIES

RELATIVE MOLECULAR MASS:

  • measures ACCURATELY the RELATIVE MOLECULAR MASS of a compound
  • each PEAK represents the substances in the sample
  • HIGHEST PEAK = more of the substance present.
  • The LAST peak on the mass spectrum ( graph) is the MOLECULAR ION PEAK- basically the X value of this peak is the RELATIVE MOLECULAR MASS- basically the relative formula mass of the entire mixture of substances.

Separating a MIXTURE  of compounds can be carried out by gas CHROMATOGRAPHY. Identifying compounds once they have been separated then uses techniques like GAS SPECTROMETRY. The pattern of peaks is like a FINGERPRINT for each unknown compound. It is matched against known compounds on a computer DATA BASE.

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