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• What are common interferences?
  
• Are two-component systems better?
  
• How do I clean and maintain my CKF system?

What are common interferences?

Anode - Cell Body Interferences
If any iodine is present in the anode solution (Coulomat A or AG) before a titration, the titration will not start and the instrument will display an "Over Dry"” message. Inject a small quantity of wet methanol or a small amount of water standard to remove this excess iodine and the titration sequence will begin. Never inject pure water into the cell body, it will exhaust your reagents sooner and cause more cleaning and maintenance.

Any moisture that seeps into the cell via a compromised injection septum or cracked o-rings are removed automatically during the "Calculating Drift" phase. It is recommend that you replace injection septa and caps with o-rings when needed.

Similarly, the anolyte can condense on the upper walls of the cell and absorb moisture. This moisture is calculated as drift or background and subtracted out of final results. In spite of the background drift being calculated out of the results, a higher drift rate will proportionally cause increasing issues. Therefore anolyte should be removed occasionally by emptying, cleaning, and drying the cell. Recommended drift rate is < 10 ug/min. Anode solution should be replaced approximately every 50 mL of samples that are injected into the cell body. A drift rate > 20 ug/min is an indicator that it is time to perform cleaning and change out the reagents.

Cathode - Generator Electrode Interference
The generator interferences, by far are the most common interference that can occur on a CKF system. To achieve the most accurate results the cathode solution should be renewed at least on a weekly or biweekly basis regardless of the quantity of water that has been injected into the cell body.

It is very important that extraneous moisture be kept from the generator chamber. When water accumulates in the generator, it is never fully eliminated because the water removing part of the Karl Fischer reaction takes place only in the anode cell body. If cathode solutions are used for too long, they will eventually create an unpleasant odor, darken the electrode, and form yellowish precipitates in the generator chamber. Similarly, if catholyte has been over used, other compounds will start to dissolve in it and reduce its concentration. This will ruin the chemical composition of the catholyte and the ability to run the KF reaction sufficiently. These interferences can seep through the diaphragm into the anodic cell body, causing high background drift rates and fouls the diaphragm. Ultimately, all interferences in the anode and generator chambers can cause the sample results to be erroneously high or low.
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Are two-component systems better?

In the beginning of the titration, protons (H+) are reduced to hydrogen (H2). You will notice titration is occurring when bubbles of hydrogen in the cathode solution appear. The diaphragm’s function is to prevent the iodine, which is generated at the anode, from being reduced immediately at the cathode. This reduction can occur in one-component system and causes erroneous readings. Therefore, two-component systems with diaphragms produce more accurate readings.

When setting up a two-component system, 5 mL of catholyte are added to the cathode generator chamber. Then 150 mL anolyte is placed in the cell body. Make sure both the catholyte and anolyte reagents are level. In two simple steps, you are ready to start CKF fast and accurate titrations on your Denver Instrument.

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How do I clean and maintain my CKF system?

Solid samples can also block this diaphragm, and therefore it is recommended that solid samples be prepped by pre-dissolving them in a suitable solvent that is compatible for your sample matrices as well as with CKF reagents. Perform a solvent blank analysis to determine the water present in the solvent to back calculate it out of the sample results. Alternatively, solid samples can use oven method in conjunction with your Denver Instrument CKF cell. Oven setups tend to be more expensive then finding a suitable solvent.

Cell Body Cleaning
The glass anode cell body is easy to clean using water or a suitable solvent like methanol. It can be dried in an oven at 70 ° C.

Generator Cleaning
The generator electrode with a diaphragm can be cleaned by placing a beaker underneath the generator while filling the generator chamber full of methanol. Let the methanol migrate through the diaphragm into the inner part of the ceramic frit and drip into the beaker below. A more stringent cleaning can be performed using a sink aspirator or vacuum. Place a beaker full of 150 mL methanol and suck the solvent through the ceramic frit. Repeat steps as many times as needed.

If there is still visible contamination on any part of the generator chamber, these procedures can be carried out with nitric or chromosulfuric acid and then repeated with methanol to rinse the acid away. If there is blackening in certain areas, the anode or cathode chamber can be dipped in nitric or chromosulfuric acid and then rinsed with a solvent like methanol. After the last rinse of methanol has evaporated, the glassware can be dried in an oven at 70°C.

Avoid using water if at all possible when cleaning the generator. This can contribute to high drift rates and exhaust your reagent sooner. Introducing water into the generator will contribute to erroneous high results.

pH and Conductivity of the samples
Dependable results from CKF titration require that the pH be maintained between 4 and 7. Samples capable of altering the pH value outside this range or that can react with iodine or alcohol may cause unwanted side-reactions that in turn contribute to erroneous result. Similarly, some samples can lower the conductivity of the reagents, which effects repeatability of the measurements. In either case a message is given of "Reagent Low", indicating the reagents have to be change out and or refreshed.
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