Moisture content is a key parameter in the manufacture of modern oral pouches, a growing area of alternative nicotine delivery. Many of the modern oral pouches emerging onto the market have high levels of moisture (30% – 50%) as a design parameter. CORESTA has developed an oven volatiles method, CRM76, which takes over 3.5 hrs to complete a measurement and so is of little practical use when considering manufacturing feedback control. The most rapid oven method takes ~10 minutes to perform.

To provide faster feedback alternative methods based upon a microwave cavity were explored and found unsatisfactory as the response curve of the cavity showed a point of inflexion at around 35% moisture resulting in uncertainty and insensitivity to moisture content above 25% moisture.

A further alternative based on the electrical properties of the pouch, using contact resistance, was developed. Correlation between CRM76 and contact resistance was possible with a simple procedure. Using a “generic” moisture curve ±5% accuracy could be routinely obtained for a sample of 8 pouch types, and where specific curves based on pouch type are adopted the accuracy with respect to CRM76 becomes ±2%. Pouch to pouch variability is clearly seen with individual pouch moisture SD of between 0.2% and 4% that is dependent upon brand. Limitations of the method are noted, the method is unsuitable for pouches with less than 10% moisture and the correlation is with oven volatiles not true water content. Finally the need for pouch type specific curves may be a function of the pH of the pouch.