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Common errors and hints -

• Types of errors
  
  
• Examples
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• Types of errors
  
  
• Errors in accuracy produce values that are unacceptably divergent to the true or correct value.
  
  
  Not to be confused with precision
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• Errors of precision will result in inconsistent values.
  
  
  Precision produces consistent results but not necessarily accurate results
  
  Errors in precision are usually systemic errors.
  
  
  
• Systemic errors are due to defective equipment operation such as defective weighing equipment
  
  
• Operator errors are caused by the operator (i.e. human error).

• securing an unrepresentative sample due to -
  
  
  • poor dispersion and integration of additions especially
    • in musts with skins
    • in large tanks
    • with additions of undissolved powdered forms
    
    
  • contamination of sample by -
    • contaminated equipment

• inaccurate preparation of standard solutions -
  
  
  • inaccurate dilutions
  • inaccurate volume/weight measurements
  • inaccurate standardisations
  • inaccurate measures of volume, weight etc.
  • contaminations

• Faulty equipment usage -
  
  
  • loss of SO₂ being aspirated through loose fitting joints
  • incorrect aspiration/flow rate (see flow rate )
  • decrease/increase in 15 min. aspiration time

• General -
  
  
  • incorrect use or reading of volumetric glassware.
  • incorrect labeling
  • contamination of solutions, glassware and/or equipment
  • deterioration of solutions and/or solution strengths
    • 0.03% Hydrogen peroxide (H₂O₂) soln. needs to be prepare daily (see preparation)
      
    • 0.01M NaOH needs to be prepared daily with 0.1 M NaOH needing protection and standardisation.
  • Errors in mathematical calculations

• Contamination of stock solutions should be avoided by pouring an estimated working volume of stock solution into a separate container (e.g 100 ml beaker).
  
  Discard working solutions after use.
  
  
• Cross contamination of solutions can be avoided by working systematically.