Ph Effect - Hach QC8500 Series 2 User Manual

6.4.2 pH effect

6.4.2.1 Common causes of pH effect
This phenomenon occurs when a change in pH occurs. Most chemical reactions are pH
dependent, therefore the colored complex that is formed as a result of the reaction may
vary in concentration if the conditions of the analysis are altered. All of the QuikChem
methods have been developed at the optimal pH of the reaction necessary for the
analysis (Figure 56).
Figure 56 pH effect
• Buffer solution with different pH: The chemistry may include a buffer reagent at a
different pH than the method specifies. This could be due to improper preparation,
contaminated chemicals, contaminated container, old chemicals, etc. Check the
recipe in the QuikChem method. Frequently, the buffer pH has to be adjusted
according to the method. Changes in the buffer preparation may also result into low
responses.
• Sample pH: Improper sample preparation and/or preservation. Determine if the
problem occurs with standards or samples to find the cause of the problem.
• Wrong pump tubes: Verify if the color of pump tubes is correct. Refer to the manifold
diagram in the QuikChem method.
• Clogs or partial clogs: Look for any blockages on the manifold. Run a dye test to
help find blockages. Refer to
• Reagent preparation: Make sure all of the reagents are properly prepared according
to the QuikChem method.
section 6.5 on page 73.
Troubleshooting
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