Hanna Instruments HI 903 - Manual (Page 211)

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TITRATION THEORY
4 TITRATION RESULTS
4.1 Accuracy
The factors most critical to achieving accurate results with the HI 900 titration systems are
the concentration of the sample, size of the sample and having an optimized set of method
parameters.
4.2 Repeatability
Repeatability, or the agreement between replicate determinations, is expressed quantitatively
as the relative standard deviation (RSD).
4.3 Sources of Error
One of the advantages of volumetric analysis is excellent accuracy and precision. The sources
of error can be grouped into sampling, titrant and standards, chemical reactions, endpoint
determination and calculations.
4.3.1 Sampling Errors
• Selection of a non-homogeneous or non-representative sample;
• Sample changed or was contaminated during collection, storage or transfers;
• Poor technique when transferring sample to beaker or flask;
• Errors in the balance, calibrate and check balance regularly.
4.3.2 Errors with Titrant and Standard
4.3.2.1 Preparation Errors
Incorrect preparation due to:
• Poor technique in weighing the salt or when transferring to volumetric glassware;
• Low-purity of salts or water used to make titrant and standard;
• Dirty or wet glassware;
• Improper storage of titrant or standard which allows water gain, evaporation or
deterioration;
• Failure to standardize frequently to adjust for change in titrant;
• Failure to flush titrator tubing with a volume of titrant before standardizing;
• Volume errors from pipettes and volumetric flasks, grade A glassware is required;
• Balance errors when weighing out salts, calibrate and check balance regularly.