Hach QC8500 Series 2, User Manual

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Troubleshooting
6.4.4.1 Common causes of carryover
• Wrong cycle period: If the cycle period is too small, carryover will occur when a
series of high standards are injected. Look up the correct cycle period in the
QuikChem method. The cycle period is specified in the Sample Timing. If overrange
samples are expected, increase the cycle period by ten seconds. Be aware that it will
take an extra ten seconds to analyze each sample.
• Wrong sample loop: Make sure the sample loop is not larger than specified in the
QuikChem method.
• Wrong standards: Verify the standards concentrations. The problem may be caused
by a standard that is higher in concentration than what the method specifies as the
high standard.
6.4.5 Flat-topped peaks
These peaks are the result of either reagent limitation or electronic limitation. The
electronic limitation is between 10 and 11 V. If the plateau of the peak is lower than 10 V,
the problem is due to reagent limitation (
Figure 58 ).
6.4.5.1 Common causes of flat-topped peaks
• Incorrect standards: The concentration of the standards may be much higher than
what is specified in the method. This may produce reagent or electronic limitation.
Make sure that the standards are not contaminated.
• Reagents: Reagents could be made improperly or the chemicals used are bad.
Check the reagent preparation procedure. A mistake in the color reagent preparation
could cause color reagent limitation. Check the age of the reagent and dry chemicals.
If they have been on the shelf for an extended period of time, they may be old and not
acceptable for running the analysis.
• Wrong sample loop: The sample loop may be too long. Verify the sample loop size in
the method.
Figure 58 Flat-topped peaks