Appendix C - Quality Assurance >>

Appendix B - Predicting Minerals by NIR

Reference:
McNunn, Lora. 1992. Predicting Minerals in Mixed Feeds. In ISI Training Manual. Perstorp Analytical.

Inorganic molecules do not absorb light energy in the near infrared regions. Mineral calibrations are based on an indirect relationship with the organic molecules due to the association of minerals with organic molecules. In other words, the NIR reading reflects something in the organic region that is correlated to the mineral composition of the sample. Since a correlation exists, a calibration can be created to estimate the mineral content. However, because the reading is not a direct prediction, errors will be much higher than for organic constituents.

Further, the correlation is only valid for minerals that are associated with the organic matrix of plant or grain tissues. When manufacturing a mixed feed, inorganic mineral sources, such as limestone, are added to the complete mix. Since these sources are not related to the organic composition of the feed ingredients, they cannot be detected by NIR instruments. Mineral calibrations created for mixed feeds would only predict the mineral composition of the organic portion of the mixed feed, ignoring any added inorganic sources. This type of calibration is erroneous and misleading because the NIR prediction will be much lower than the expected value, based on the known amount of added mineral.

Similarly, calcium added to soymeal as a "flow agent" cannot be detected by NIR.

NIR can only be used to estimate macro mineral content of organic tissues (excluding inorganic additions, dirt, etc.) and that any result outside of a normal range must be verified by reference methods.

Appendix C - Quality Assurance >>

[ Table of Contents ]