Analysis of Iron

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Analysis of Iron

• Experiments 3, 19 20

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Experiment 3- Gravimetric Determination of Iron
as Fe2O3

• Gravimetric analysis is the quantitative
  measurement of analyte by weighing a pure, solid
  form of the analyte.
• Since gravimetric analysis is an absolute
  measurement, it is the principal method for
  analyzing and preparing primary standards.

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Advantages Disadvantages of Gravimetric Analysis

• Advantages
• Provides precise analysis, this process was used
  to determine the atomic masses of many elements
  to six figure accuracy.
• Provides little room for instrumental error and
  does not require a series of standards for
  calculation of an unknown.
• Doesnt require expensive equipment
• Also used to calibrate other instruments

• Disadvantages
• Provides for analysis of a single element
• This method is often complicated and the
  slightest error in procedure will mean disaster
  in analysis

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Experiment 19- Spectrophotometric Determination
of Iron in Vitamin Tablets

• The Beer-Lambert Law states that for
  monochromatic light (one wavelength) absorbance
  is proportional to length and concentration of
  the species.
• This means that if concentration doubles,
  absorbance will also double. If length triples
  then absorbance triples. If concentration is cut
  by half then absorbance will be cut by half.
• We are using the Beer-Lambert Law in a
  quantitative way, to determine the amount of iron
  in our vitamin supplement.

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Spectrophotometric Accuracy and Advantage

• Most accurate at intermediate levels of
  absorbance, A0.4-0.9
• If too little light gets through the sample (high
  absorbance), the intensity is hard to measure.
• If too much light gets through the sample (low
  absorbance), it is hard to distinguish the
  difference between the sample and the reference.
• The advantage with the Spectrophotometric a much
  more efficient method.

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Experiment 20- Microscale Spectrophotometric
Determination of Iron in Foods by Standard
Addition

• The experiment was similar to experiment 19
  except that this experiment dealt with smaller
  volumes.
• Standard addition is used in instrumental
  analysis to determine concentration of an analyte
  in an unknown sample by comparison to a set of
  samples of known concentration, similar to using
  a calibration curve.

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Spectrophotometric by Standard Addition Advantages

• Applied to most analytical techniques and is used
  instead of a calibration curve to solve the
  matrix effect problem. (The matrix effect problem
  occurs when an unknown contains many impurities)

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Summary of all 3 Methods