Automated moisture/ash determination in feed

A fully automated method with high sample throughput for moisture and/or ash analysis by loss on weight principle…

Michael Jakob
European Field Product Manager
LECO Europe

The determination of moisture and ash is an important standard parameter in animal feed analysis. There are several possibilities to do this e.g., with traditional drying oven/muffle furnace methods or with NIR/NIT technology. One of the most common moisture determination methods is mass loss-on-drying or mass loss on ignition/combustion utilizing an air oven or a muffle furnace for ash determination.

This technique involves recording the sample mass before and after exposure to an elevated temperature in an oven (typically ~ 105°C) with air ventilation for moisture. Ash is normally done at higher temperatures like 550°C or even up to 900/1000°C for some materials. After a certain time or after checking of the weight constancy the analysis is considered for being ready.

Picture 1: TGA 801 Crucible placed on the built in balance        Picture 2: TGA 801

The resulting sample mass loss is calculated and represents the moisture and/or ash content of the sample. In this article an automated moisture/ash determination system will be described that is using weight loss on drying/combustion method for the determination of moisture and ash.

The LECO TGA 801 is a macro thermogravimetric analyzer that is widely used for the determination of moisture and ash content of food and feed. Nineteen (or thirty-eight) samples, with sample weights of up to 5 g can be analyzed simultaneously. Both parameters are analyzed in one run, just by running one step after the other. The system is fully automated, so only sample input must be done manually.

Picture 3: TGM 800 – Moisture only analyzer.

The samples are weighed directly into a ceramic crucible, the crucible is in a sample carousel that moves every crucible sequentially onto a balance pedestal where the sample weights are measured throughout the analysis sequence using an integrated 4 place balance. The carousel has a capacity of 19 samples plus one empty reference crucible for buoyancy correction. Weight loss is recorded for a fixed time or until weight constancy has been determined. When all samples show weight constancy for moisture, then the next step (e.g. ash at 550°C) can start and the instrument will automatically determine this parameter.

If moisture only is needed as a parameter there is also a system with the same working principle but limited temperatures (up to 175°C) available, the TGM800.

Typical results for moisture and ash analysis in feed samples are shown in Table 1. As seen, the results have a very high precision generally for homogenous samples an RSD of <0.5% can be expected. Most feed and food samples can be analyzed with the system using the same analytical setup.

In comparison to the manual method, you will see an example in Table 2 that the results are perfectly matched for this specific sample. Moisture and ash values are precise and accurate, and the standard deviation is in most cases smaller compared to manual methods. The analysis time is normally significantly shorter with the TGA method compared to the manual measurements, since the desiccator step is not needed, and mass constancy is automatically determined during the run.

Moisture and ash – determination with automated primary TGA methods is saving time and manual labor of the lab. The TGA and TGM systems are working simultaneously for multiple samples with full documentation of the sample results and all method steps. Generally, the critical requirements of analytical standard methods like temperature control, mass resolution and precision, furnace atmosphere and flow, analysis time or mass constancy criteria can be matched.

About Michael Jakob
Michael Jakob, European Field Product Manager at LECO Europe, studied material science at the FAU Erlangen-Nürnberg. Since 30 years Michael is working for LECO in different positions. He is responsible for technical information and communication of analytical methods and procedures.