Moisture levels matter

Being able to measure moisture content accurately is critically important in a variety of industries. In the food and beverage sector, for example, too high a water content leads to reduced shelf-life as moulds appear earlier than the suggested ‘Best before date’ – typical eg in dry fruits. Too low a water content, on the other hand, impacts the taste and texture of the product. 

It can also affect profitability. Butter is regulated to have a 15% water content and producers are averse to any lower as this would lead to reduced profit margins. In the oils and fuels sector, mean-while, incorrect water measurement can have seri-ous cost implications, with buyers potentially over-charged for the oil they purchase. High moisture content can also make the oil conductive, leading to short-cuts in generators and safety hazards. In aviation fuel, if water content is too high, the fuel can freeze when airborne and cause serious risks. 

Pharmaceuticals, however, are even more sensitive to inaccurate water determination, with production stoppages every time an error is detected. Pharma products also require special handling. For example, lyophilised or freeze-dried vaccines are very hygroscopic and require special techniques to work in controlled environments to avoid moisture absorption and inaccurate results. 

Since its invention in the early 1900s, Karl Fischer (KF) titration has been the most accurate technique for moisture analysis. Superior accuracy aside, it has gained popularity due to several practical advantages over other methods of moisture determination, such as increased speed and selectivity. 

Despite the long history of use, unfortunately some process errors are often repeated, caused most frequently by lack of expertise. Karl Fischer titration is typically not taught in universities or during apprenticeship. Chemists and sometimes non-chemists typically learn the method on the job and while standard operating procedures (SOPs) are helpful, they don’t necessarily prevent errors caused due to the lack of knowledge.

Common KF titration errors include:

• Unawareness of side reactions. For instance, a sample may react with the solvent to create or consume water, resulting in inaccurate water determination. This error is prevalent in oils and chemicals, but can affect other sample types too. 
• Poor sample solubility. A sample may not fully dissolve and therefore render water determina-tion inaccurate. Food and beverage is one of the industries struggling with this issue the most.
• Incorrect sample handling. A sample may lose or take up additional water during incorrect sample handling resulting in inaccurate read-ings. This is often seen in the pharma sector.
• Incorrect calibration of KF instruments. Instrument performance may vary over time with use. Proper functioning requires regular checking of calibration using water standards.
• Choosing the wrong method. Sample needs vary and there are a variety of factors to consider when choosing a method. Making the wrong choice leads to multiple additional errors. 

Of these five errors, the last two stem from a clear skills gap that can be reduced with proper training. The others are more challenging and require more experience to understand and correct. In fact, an expert might suggest modifications to the standard Karl Fischer technique. Examples of such errors that frequently impact water determination in critical industries can be specific to industry sector. 

A critical challenge working with food samples, for example, is that they don’t dissolve easily and the method must be adjusted for accurate results, such as using a homogeniser/disperser or heating up the titration vessel in advance.

For oils and fuels, it is important to note that oils contain additives for performance, which not only lead to poor solubility in common alcohol-based Karl Fischer reagents, but also often cause side reactions during titration that lead to incorrect readings. To avoid these, it’s suggested lab analysts use an indirect method, such as the KF Oven, which avoids contact with the additives, buffering the KF vessel to suppress the side reactions. Alternatively, they can consider working with specialised methanol free reagents, suitable for titrating oils. 

Determining the water content of plastics presents another interesting challenge since they do not dissolve at all in Karl Fischer reagents. Again, indirect techniques like the KF Oven can be used to accurately determine the true water content. This however requires knowledge of the temperature range that would yield accurate results. It is critical to determine water content accurately. If water content is too high, it may evaporate during plastic moulding and/or production, leading to rough and porous surfaces. Automobile and electronic components routinely face this issue. 

Looking at the various KF titration issues commonly requiring troubleshooting, it’s clear that know-how is the key component, besides proper equipment and perfect reagents.