Powders and other bulk solids represent a wide array of products across nearly all industries. From food products like milled flours and flavorings to inorganic powders used in the plastic industry, moisture matters for all types of powders.
Before final processing, it is important for these materials to be within a certain moisture range to uphold internal and external quality standards. The moisture level of these products may change while being stored in intermediate warehouses or from being shipped in bulk around the world.
Standard oven and vacuum oven methods have been have been used to monitor the moisture levels of these products with a high degree of accuracy. However, using these methods have proven to be quite lengthy with test times ranging from 30 minutes to several hours or even days. No matter what the industry, test times such as these may be too long for a practical business approach in such a fast-paced economy.
A rapid loss-on-drying (LOD) Instrument for bulk solid moisture analysis uses the same theory as standard oven methods:
- An empty sample pan is weighed and tared
- Sample is added and recorded as the initial starting weight
- Heat is applied to sample to evolve moisture (or other volatiles)
- Difference in sample weight is recorded and calculated as % Moisture using the equation
With a rapid LOD instrument, the balance and heat source are coupled together allowing the user to view real-time moisture curves and rate graphs as moisture is evolved. In the integrated system, test times are substantially faster with the same level of accuracy one would expect from traditional oven methods.
Using the Computrac® MAX® 4000XL Moisture Analyzer, various powdered samples were run in tandem with traditional oven methods to determine moisture content. Samples included flour, food flavorings and inorganic polymers ranging as high as 14% moisture to as low as 0.03% moisture. The instrument is robust and designed for onsite analysis using small sample sizes (<40 g). Along with being able to view real-time graphs during each test, data from each run can also be stored via Ethernet connection or USB memory stick for graphical analysis.
Sample Prep – All samples tested were analyzed as they were received from the manufacturer. Samples were stored in air tight Mason jars to prevent excessive desiccation during testing.
Test Conditions – For flour samples AOAC 925.09 or 925.10 methods were used. For all other samples a modified 925.09 or AOAC 925.45 were used.
Computrac® MAX® 4000XL – Flour Samples
Test Temperature: 150 °C – 170 °C
Results Display: % Moisture (3 or 4 decimals)
Computrac® MAX® 4000XL – Food Powders
Test Temperature: 85 °C – 120 °C
Results Display: % Moisture (3 or 4 decimals)
Computrac® MAX® 4000XL – Inorganic Polymers
Test Temperature: 75 °C – 160 °C
Results Display: % Moisture (4 decimals)
For information regarding specific parameters for each sample, contact Arizona Instrument LLC for further assistance.
All samples were sifted evenly over waffle pan and run using parameters listed above. Flour samples that were analyzed using these methods included All-Purpose, Pastry, Whole Wheat, Soy, Black Bean, and Pinto. Food powders samples included Vanilla, Tomato, Blueberry, Parmesan, and 3 different cheese powders. The last set of samples included inorganic powders named polymer 1, polymer 2 and powder coating. All trade names and manufacturer names were withheld for this study.
Figure 1 represents a typical graph of whole wheat flour that can be viewed during routine testing. The blue line corresponds to the % Moisture while the red line corresponds to the Rate (% loss per minute). The data was downloaded into Microsoft® Excel® and graphed using graphical analytical tools in Excel®. Once a rate drops below a set ending rate the test will terminate. (time, prediction, temp then rate are also other ending options that can be used)
Figure 2 shows a set of flour samples analyzed with their corresponding oven method. All oven and MAX® 4000XL tests were performed in triplicate (x3). Error bars represent the standard deviation (S.D.) of the individual data set.
The array of flour samples demonstrate equivalency to their corresponding oven reference methods at various moisture levels.
It is also important to test other material to demonstrate the versatility of the MAX® 4000XL. Figure 3a &3b are a collection of food powder flavors that also demonstrate the MAX® 4000XL’s equivalency to the oven method as well as maintaining a tight standard deviation (error bars). Figure 3b consists of three ‘cheese powder’ samples which highlight the resolution of the instrument measuring these slightly varying moisture levels from the same product.
Table 3 represents the raw data from ‘Cheese 1’ to demonstrate the significant difference in test times.
Figure 4 presents another variety of samples analyzed by both standard oven and rapid LOD methods. This set of data corresponds to the inorganic powders used in the plastic/coating industries. The data demonstrates that even at low moisture levels, accuracy and precision are not compromised on the MAX® 4000XL as seen by the error bars (± S.D.).
Table 4 represents the raw data with statistics of figure 4. The MAX® 4000XL (4K) has a smaller S.D. than the oven even at low moisture levels when run in triplicate.
A rapid loss-on-drying (LOD) instrument such as the Computrac® MAX® 4000XL allows the technician to accurately and precisely measure % moisture at high and low levels in various powders. Data presented in this paper demonstrate that test times are substantially shorter when compared to standard oven references, with virtually no prep work (no need to purge pans or allow for cool time). Having a real-time graphing LOD unit, allows the technician to view the rate of loss as its occurring or digitally save it for later analysis. This is helpful in determining the appropriate ending criteria and maximizing the efficiency of each test. Using the MAX® 4000XL will save both time and money and is robust enough to withstand the stresses of a distribution or manufacturing floor.