Titration Results; Accuracy; Repeatability; Sources Of Error - Hanna Instruments Hi934 Bedienungsanleitung

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4. TITRATION RESULTS

4.1. ACCURACY

The factors most critical to achieving accurate results with 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 transfer
• Poor technique when transferring sample to beaker or flask
• Errors in the balance (calibrate and check balance regularly)
4.3.2. 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)
4.3.3. DISPENSING ERRORS
Incorrect dispensing due to:
• Dead valve volume and leaking valve
• Inaccuracy in motor drive and gear lash/backlash
• Poor burette/piston seal
• Non-uniform diameter of burette glass cylinder
• Chemical incompatibility with tubing or bubble generation
• Density/temperature changes in titrant
• Inadequate volume to cover electrode
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HI900 titration systems are the concentration of the