It depends on the water content of the samples. For medium to high water content the most suitable option is to use volumetric KF, as it is appropriate for analyzing samples containing 0,1% to 100% of water. For those samples with water content between 10ppm and 1000ppm, the method of choice should be Coulometric KF, as volumetric KF may not be sensitive enough.
One-component reagents contain all the necessary compounds for the reaction in one bottle. It is simpler than, but not as fast as two-component reagents, since their pH (pH=5) means the reaction time is slower. Their shelf life is shorter because iodine and SO2 together are less stable, but is the best option if your sample requires the addition of modifiers to the solvent such as chloroform. Two component reagents’ pH value is 6. In this case, its less acid pH makes the reaction faster, allowing some reactions to be completed in as short a time as 1 minute. It is marginally more precise and, since iodine and SO2 are not combined, its shelf life is longer than that of one-component reagents.
In this case we would recommend using two-component reagents, but replacing Aquagent Solvent by a more specific solvent to help dissolve fats and oils such as Aquagent Solvent CM and Aquagent Solvent Oil. Aquagent Solvent CM contains chloroform, which improves the solubility of long-chain hydrocarbons. Aquagent Solvent Oil contains 1-hexanol and avoids using halogenated hydrocarbons.
For optimum results we advise using specific reagents. Aquagent® KF Reagents contain methanol as the solvent. Aldehydes and ketones in contact with methanol lead to a side reaction that results in water formation. The results using a standard methanol-containing reagent would not be reliable as the amount of water measured would be higher than the real water content of the sample. In this case it is best to use our Aquagent Complet K and Aquagent Medium K, both free of methanol and optimized to provide the best results when working with aldehydes and ketones.
In this case we would recommend adding dry formamide to the solvent. The ratio should be 20:10 methanol:formamide, and then use a one-component reagent. We do not recommend using coulometric KF to analyze this kind of sample.
An acid sample can be analyzed by volumetric KF, either using one-component or two-component reagents. If your choice is one-component reagents, our recommendation is to add Aquagent Buffer Acid to the solvent to neutralize the acid. If you prefer to use two-component reagents, some Aquagent Buffer Acid should be added to Aquagent Solvent. The amount of Aquagent Buffer Acid that should be added in each case depends on the sample; its buffer capacity is 5mmol acid/ml buffer.
If acid samples are to be analyzed using a coulometric KF, it can be done using both cells with and without diaphragm, just adding 20g imidazole/100mL of reagent.