KF VS LOD

In pharmaceuticals, several methods are employed to determine the water content of a substance/product. Among which Karl Fischer Titration (KF) and Loss on Drying (LOD) are most honored and largely reliable methods.

Loss-on-Drying (Weight Loss)

This method uses the principle of drying a sample of the product and comparing the weight before and after drying. The difference in weight represents the moisture that is in the product. This can be accomplished by using various manner such as drying ovens, infrared balances, and infrared lamps. Whatsoever, the drying conditions are strictly specified. The difference in weight after drying is due to the loss of all evaporated matter, which is taken to represent the moisture content. Repeatability and accuracy of this method solely depend up on the temperature and time controls adopted during testing.

The difficulty is that this technique measures all the moisture lost from the sample, which includes not just water but also any other volatile component already present in the sample (like residual volatile solvents) or created by polymerization or degradation of the sample.

Karl Fischer (KF) Titration

Karl Fischer titration is a very specific determination method which detects and measures only water, including water of crystallization and surface-absorbed water. It is based upon a redox reaction involving water and iodine in the presence of a base, an alcohol, and sulfur dioxide. The water-iodine reaction is dependent upon the presence of water, and therefore the titer of reagent used up in the reaction reflects the amount of water in the sample as there is no other source of water.

The KF reagent contains iodine and when it has completely reacted with the total water, excess iodine appears in the solution, causing a color change as well as an electrometric change which can be detected by a double platinum electrode. KF titration measures total water and is not affected by the presence of residual volatile solvents. It has a wide and sensitive range of determination from a water content of 100% to 1 ppm.

KF	LOD
KF is a method, which measures only the water content (i.e. it's water-specific) in a product sample.	LOD on the other hand, measures the total change in weight of a material as a result of drying. For some products, components such as alcohol or fat evaporate with the water. Therefore, the LOD method measures both the water and volatile impurities such as those mentioned previously
Karl Fischer titration is a chemical method. It involves adding a reagent to the sample to cause a reaction that converts the water in a product to a non-conductive chemical.	Loss on Drying compares the weight of a product before and after it is dried. This difference in weight is taken as the percentage of moisture in the product.

Key Words Loss On Drying Water determination LOD Vs KF Karl Fischer Vs Loss –On Drying –Which Method is Best?