When a measurement problem arises, it is best to try to locate the cause first. Here's a list of all possible reasons that might cause measurement issues:

• Is there sample carryover?
• Are there sample interferences or complexing agents present?
• Is the reference electrode junction contaminated?

• Was the electrode stored in the wrong solution?
• Was the electrode poisoned by the sample?

• Is the electrode plugged into the controller properly?
• Is there a reference electrode present?
• Is there enough fill solution left in the reference electrode?
• Is the electrode placed in the sample solution?

• Are the standards too old, contaminated, or made wrong?
• Has the sample pH been adjusted properly to the operating range of the electrode?
• Is there an air bubble on electrode surface?
• Is the controller okay?
• Is there enough fill solution left in the reference electrode?

• Is the controller grounded?
• Is there an air bubble on electrode surface?
• Is the controller operating properly?
• Is there enough fill solution left in the reference electrode?

• Is there excessive leaking at the reference electrode junction?
• Is the reference electrode junction clogged?
• Was the sensing membrane poisoned by the sample?
• Are there temperature problems?
• Is the sample too concentrated?
• Does the sensing membrane need conditioning?

• Are the standards incorrect?
• Was the sample pH adjusted properly?
• Is there sample carryover?
• Are there sample interferences or complexing agents present?