Moisture Content Analysis in Powder Samples

An introduction to Moisture content analysis:
People often encounter moisture in their daily lives, whether through humidity in the air, the dampness of clothes, or the moisture content in food. High humidity levels, such as those in Dubai or the Asian tropics, can affect comfort and health, prompting the use of dehumidifiers or multiple air conditioners (AC). Moisture refers to the presence of water, typically in the form of tiny droplets or vapor, within a material or the atmosphere. It is formed through processes like evaporation, where water transitions from a liquid to a gaseous state, and condensation, where water vapor cools and changes back into liquid droplets, such as when hot 45-degree air hits the windows of a villa with the AC running at 19 degrees Celsius.

Regardless, moisture is vital for life, providing the necessary hydration for biological processes in plants, animals, and humans. In the context of powder technology, moisture content is key as it affects the flow, compaction, and stability of powders in general. Adequate moisture can prevent powders from becoming too dry and dusty, facilitating better handling and processing. However, excessive moisture can lead to clumping and reduced shelf life, impacting the quality and usability of powders. Therefore, balancing moisture levels is beneficial in optimizing the performance and longevity of powders in various industrial applications. So, while not always at the forefront of our minds, moisture significantly impacts daily routines and activities across various contexts. That’s why Moisture content analysis is of utmost importance.

Understanding Moisture Content

Moisture content refers to the amount of water present in a material, usually expressed as a percentage of the material’s total weight. In powders, moisture can exist in various forms, such as free water on the surface, as water bound within the particles, or as chemically bound water. Accurately determining the moisture content is important for controlling product quality, optimizing storage conditions, and ensuring smooth processing.

In powder processes, managing moisture content is essential in preventing bacterial growth, in addition to ensuring flowability, stability, reactivity, and shelf life. The critical factor for inhibiting bacterial growth is water activity (aw), which measures the free moisture available for microbial proliferation, ranging from 0 (completely dry) to 1 (pure water). Bacterial growth is significantly inhibited at water

activities below 0.6 aw, with most bacteria unable to thrive under these conditions. However, some molds and yeasts can grow at slightly higher water activities, typically around 0.7 aw. While the specific minimum moisture content varies depending on the powder’s composition, maintaining a low water activity is a reliable indicator of safety. The 0.6 aw moisture level, often referred to as the (safe moisture level) or (critical moisture content), is essential to preserve the overall integrity of powdered products.

Regulatory guidelines, such as those provided by the U.S. Food and Drug Administration (FDA), and the European Food Safety Authority (EFSA). In Asia, countries like Japan and China also have strict regulations through agencies, such as the Ministry of Health, Labor and Welfare (MHLW) in Japan and the National Health Commission (NHC) in China. The International Organization for Standardization (ISO), establishes comprehensive and acceptable moisture safety

standards for moisture content. For instance, the FDA Food Code and various compliance policy guides detail these standards for food safety, while ISO 21807:2004 offers guidelines for determining water activity in food and animal feedstuffs.  By adhering to these standards, the risk of bacterial contamination and other moisture-related issues in powders can be effectively minimized, ensuring product safety and longevity on a global scale.

Moisture content also plays a significant role in the properties and performance of powder materials, affecting their stability, flowability, reactivity, and shelf life. Accurate determination of moisture content is essential in various industries, including pharmaceuticals, food processing, agriculture, and materials science, where it ensures quality control, optimizes processing conditions and complies with industry standards.

Gravimetric Method

Presently, the gravimetric method is one of the most widely used techniques in determining moisture content. Test samples are weighed before and after drying, the difference in weight will represent the amount of moisture lost. The procedure typically involves placing the sample in a drying oven that is usually set between 105°C and 110°C for a pre-defined period. After drying, the sample is cooled in a desiccator to prevent moisture absorption from the environment and then reweighed. This method is commonly used in the food and pharmaceutical industries due to its simplicity and accuracy. However, its simplicity comes with a drawback, it is quite time-consuming and unsuitable for materials sensitive to heat because high temperatures could cause decomposition or chemical changes to the sample. A similar method is the Loss on Drying (LOD) where the sample is also heated to remove moisture. The sample is weighed before and after drying,

measuring the total amount of volatile substances, including moisture, that are lost upon heating. This method is widely used in the food and pharmaceutical industries because of its simplicity and minimal equipment requirements. However, it does not always distinguish between water and other volatile substances, possibly leading to inaccuracies.

Similarly to the previous methods, the thermogravimetric analysis also uses heat in a controlled environment to measure a sample’s weight change, providing detailed information about the sample’s thermal stability and moisture content. The weight loss at different temperatures indicates the presence of moisture and other volatile substances and is used in materials science and pharmaceuticals. The thermogravimetric analysis provides comprehensive data on weight changes and decomposition temperatures. However, it requires specialized equipment and interpretation of more complex data.

Karl Fischer Titration

Another method used in testing moisture content is the Karl Fischer titration technique which is a chemical method specifically designed to measure water content using a water reacting reagent. This testing method is highly accurate and is extensively used in pharmaceuticals and other industries where precise moisture determination is a critical factor.

The procedure involves dissolving or dispersing the powder sample in a suitable solvent, followed by the addition of the Karl Fischer reagent which is a solution of iodine, sulfur dioxide, and a base of methanol. After which the water content is determined by the amount of reagent consumed. Its main advantages include high specificity for water and accurate results, even for low moisture content. However, it requires careful handling of the chemicals used and accurate calibration of the titration system.

Infrared (IR) Spectroscopy

As with Karl Fischer titration, Infrared spectroscopy also requires careful calibration but could be less accurate since it may be affected by other components in the sample that absorb infrared light. This method measures the absorption of infrared light by the sample, which correlates with its moisture content. In this technique, the powder sample is exposed to infrared light, and the absorption at specific wavelengths corresponding to water is measured. The moisture content is calculated based on the absorption intensity. Infrared spectroscopy is used in various industries for non-destructive, fast moisture analysis, and its ability to be used in continuous monitoring such as water content in milk powder during production, soil moisture levels in agricultural fields, reaction mixture during chemical synthesis, and the monitoring the atmosphere

Dynamic Vapor Sorption

within controlled environments like greenhouses, to name a few. Out of several other methods not covered, dynamic vapor sorption (DVS) is worth mentioning.  DVS is mainly used in pharmaceuticals and the food industry to study hygroscopicity and moisture-related properties. It provides detailed information on moisture sorption kinetics and equilibriums. Unlike the previously mentioned methods using light or heat, DVS measures the sample’s moisture uptake and loss, while it is exposed to varying humidity levels.
In a chamber with controlled humidity, the weight change of a sample is measured as the humidity changes, providing a profile of moisture sorption and desorption. Although it gives accurate data, it is a time-consuming method that requires precise control over the humidity and temperature scales.

Applications Across Industries

In pharmaceuticals, moisture content analysis ensures the stability and efficacy of drug formulations, prevents degradation, and optimizes storage shelf life. Excess moisture can also lead to the formation of unwanted compounds or affect the drug’s dissolution rate and/or bioavailability. In the food industry, moisture content affects texture, taste, and the product shelf life, making it essential for quality control and regulatory compliance. In agriculture, moisture content impacts the quality and storage of products, preventing spoilage and loss. Moisture content also plays a significant role in materials science, exerting influence on the processing and performance of various materials, especially ceramics, coatings, and composites. Here, moisture can affect the curing process and the mechanical properties of the finished material.

Future Directions of Moisture content analysis

Despite advancements in moisture content analysis, several challenges still remain. Sample variability can lead to inconsistent results, requiring consistent human effort and attention to sample preparation and handling. Continuous instrument calibration and maintenance are essential for reliable measurements. Additionally, selecting the appropriate method based on material properties and required accuracy can cause delays.

As technological advancements continue to unfold even in moisture content analysis, artificial intelligence (AI) could eventually play a central role. AI technology could offer solutions such as advanced sensors for real-time monitoring, which can provide continuous feedback on moisture levels. Additionally, AI-driven automation in sample preparation and analysis would reduce or even eliminate human error, enhancing overall efficiency. By integrating AI and machine learning algorithms that never get tired and that will perform the same task 10,000 times with the same accuracy, data interpretation and predictive analysis will also be significantly improved, leading to more accurate and insightful insights into moisture content dynamics. As a result, full AI-driven systems have the potential to drastically change moisture content analysis, offering enhanced precision and reliability in various industrial applications due to the overall systemic complimentary nature it will offer.