It’s the water that matters: that simple statement turns out to be true more than some people might imagine. The moisture content of numerous products, from cantaloupes to semiconductors, impacts crucial properties, and an accurate moisture analyzer is essential to ensure product quality.
Also known as moisture balances, these devices measure how much weight a sample loses as it dries. Some equipment can detect very low moisture levels—in the parts per billion by volume—in a sample, which might range from foods and pharmaceuticals to soils and sludge.
“For food and pharmaceutical manufacturers, cosmetics producers, and others seeking to ensure consistent uniformity through each stage of production, moisture determination is a necessary step in product quality,” explains John Viero, senior director of lab essentials at Cole-Parmer. “The moisture content can reveal properties of the material relative to purity, concentration, stability, shelf life, and nutritional value.”
Selection criteria for moisture analyzers
Selecting the best moisture analyzer for a lab depends on a range of features, such as the technical specifications. For example, potential customers should review a device’s datasheet to make sure that it can meet the necessary detection levels, and to ensure it is suitable for the sample types to be analyzed. Some samples, such as volatiles, can require special handling. Also, keep in mind how many operators might use a device and how much experience they might have. Less experience in the operator requires a device that’s easier to use.
Another distinguishing feature comes from how a device dries a sample, which can be hastened with a halogen or infrared (IR) heat lamp. “Halogen lamp heating elements are suited for applications that require accelerated temperature regulation during sample drying,” Viero explains. “Halogen heats up quickly and provides improved repeatability over infrared, plus it is not as costly as microwave types.” On the downside, a halogen lamp can heat so fast that it scorches a sample. Conversely, IR is not as fast and repeatable as halogen, but an IR-based moisture analyzer is less expensive.
After making the IR-versus-halogen decision, Viero recommends some specific features to consider before buying. For example, a moisture analyzer should provide built-in operational modes that fit the intended applications. Plus, the device should log information like the ambient conditions during a measurement, the user, drying mode, and other needed information.
Connectivity should also be considered, and the method should meet good laboratory practice (GLP) or good manufacturing practice (GMP) standards. Then, Viero says, devices might include a variety of connectivity methods, including RS-232, USB interfaces, Ethernet port, or a Wi-Fi external connection to a computer or printer.
A moisture analyzer also needs testing over time—some of that can be performed by a user, but some factory adjustments or repairs could eventually be required. A vendor should provide information on options for service.
Comparing heating modes of moisture analyzers
Moisture analyzers fill an obvious need in the food industry, especially for analysis of storage methods. It’s easy to imagine how food stored at the wrong moisture content would end up with an unappetizing consistency—noticeably soggy or hard or just not quite right. In the food industry, halogen-based moisture analyzers have been used for some time. In 2014, researchers in India used one of these devices to analyze the quality of red-chili fruits after vacuum packing and long-term storage. Here, the scientists showed that just a two percent difference in the moisture content of the stored chilies impacted the quality of the product.
Given the long history and wide-ranging use of moisture analyzers, it seems like scientists could easily find independent data on performance, but that’s not always the case. Just one year ago, a group of scientists working in France explored halogen technology to measure the moisture content in powders. The researchers pointed out that halogen-based drying is considered the top choice for moisture analysis in powders due to the technology’s accuracy, reliability, and speed, but they added that there’s little or no data to support those claims. So, this team took on that task: comparing a halogen analyzer with three reference thermogravimetric instruments on 14 powders across a range of chemical compositions. The halogen device produced data with a five percent coefficient of variation—not significantly different from the thermogravimetric platforms tested. The scientists concluded that these devices do make a good choice for moisture analysis in powders, especially for small companies and labs that cannot afford more expensive methods, such as microwave-based drying.
Build your own moisture analyzer
Some scientists prefer to make their own instruments where possible. A research team in France, for instance, made a moisture analyzer based on a capacitive sensor. Although the researchers considered this to be a prototype only, they found that it equaled the performance of many commercial devices.
Beyond a DIY spirit, some circumstances require novel approaches to moisture analysis. That’s what one group of scientists in Japan concluded when analyzing semiconductor devices, which require a water concentration below one part per million by volume. Using a ball surface acoustic wave sensor and custom sampling electronics, this team developed an analyzer that could detect water at 0.05 parts per billion by volume.
From a design bench to a catalog, many options exist for moisture analyzers. The best choice depends on how a device meets the criteria for a particular application. On a planet with more than one billion cubic kilometers of water, there will be moisture to analyze for a long, long time.