New Calibration Trick Makes Mineral Testing in Animal Feed Faster and More Accurate

Every mineral analysis in a feed laboratory faces the same stubborn problem: the sample itself interferes with the measurement. When scientists dissolve animal feed and try to measure its calcium, iron, or zinc content with a plasma spectrometer, components of the feed matrix can suppress or distort the signals from the very elements they want to quantify. A research team from Brazil has now demonstrated that a calibration strategy known as Multi-Signal Calibration, or MEC, can sidestep this interference, delivering faster and more accurate mineral profiles of animal feed using two common instruments: inductively coupled plasma optical emission spectrometry with either radial or axial viewing configurations.

The principle behind MEC is elegantly simple. Instead of relying on a single emission line for each element, the method exploits the fact that a plasma spectrometer records multiple emission lines simultaneously for every element in the sample. The researchers prepare two solutions: one containing the sample spiked with a known amount of analyte, and one containing the unspiked sample. They then plot the signals from these two solutions against each other across all available emission lines. Because the spiked and unspiked solutions differ only by the known addition, the resulting plot reveals the analyte concentration directly, while interference effects that affect both solutions equally cancel out in the comparison.

The team applied this strategy to real animal feed samples, measuring ten elements: calcium, phosphorus, sodium, magnesium, iron, zinc, copper, manganese, cobalt, and molybdenum. For each element, they recorded multiple emission lines and constructed the calibration plots. Emission lines that showed interference appeared as outliers in the plots and were discarded, a diagnostic feature that the researchers highlight as a key advantage of the method. Rather than guessing which lines are trustworthy, the calibration itself identifies the problematic lines.

To evaluate accuracy, the team analyzed certified reference materials, including bovine liver and a mineral supplement from the Brazilian Agricultural Research Corporation, EMBRAPA. The measured concentrations agreed well with the certified values, demonstrating that the method recovers true elemental content in complex biological matrices. The researchers also compared their results with those obtained by conventional calibration with external standards, finding that MEC delivered comparable or better accuracy without the need for extensive matrix matching.

Detection limits achieved with the method were competitive with those reported in the recent literature. For most elements, the limits of quantification fell in the low microgram-per-gram range, sufficient for the mineral levels typically found in animal feed. The team notes that the multi-signal approach can even improve detection limits for some elements, because averaging information across multiple emission lines reduces the impact of noise on any single line.

Precision was another strong point. The relative standard deviations of replicate measurements were generally below ten percent for most elements, and often below five percent, meeting the quality requirements for routine feed analysis. The researchers emphasize that the method requires no additional instrumentation beyond what a standard plasma spectrometer already provides, making it accessible to any laboratory with existing equipment.

The implications for animal nutrition are significant. Feed formulations depend on accurate mineral profiles to ensure that animals receive adequate calcium, phosphorus, and trace elements for growth, bone development, and immune function. Errors in mineral analysis can propagate into feed formulations, leading to deficiencies or excesses that affect animal health and productivity. A calibration method that reduces matrix interference and improves accuracy directly supports better feed quality control.

The team also highlights the practical advantages for busy laboratories. Because the calibration uses the sample itself as the matrix, there is no need to prepare extensive matrix-matched standards or to apply complex correction procedures. The two required solutions, spiked and unspiked sample, are straightforward to prepare, and the calibration plots are constructed automatically by the instrument software. The entire workflow integrates into existing routines with minimal disruption.

The researchers conclude that the multi-signal calibration strategy represents a practical, accurate, and accessible approach for mineral analysis in animal feed. By exploiting the full spectral information that modern plasma spectrometers already record, the method turns a longstanding source of error into a diagnostic tool, identifying interference and correcting for it in a single step. As feed laboratories worldwide face increasing demands for rapid, reliable mineral profiling, this calibration trick offers a way to meet those demands with the instruments they already own.

The study behind these findings was conducted by researchers at the Federal University of São Carlos and the Federal University of Mato Grosso in Brazil, together with collaborators at the National University of La Pampa in Argentina, and was published in Frontiers in Analytical Science in February 2025. The work focused on thirteen swine feed samples collected from a local farm in La Pampa, Argentina, covering the full range of physiological stages in a pig’s productive life. These included growth stages for animals weighing between three and fifty kilograms, development and completion phases extending up to eighty kilograms, and finishing categories that reached bristle animals between eighty and one hundred twenty kilograms, as well as gestating and lactating sows. This life-stage coverage matters because mineral requirements shift considerably as animals grow, reproduce, and lactate, so a calibration method must perform reliably across widely varying feed compositions.

Sample preparation played a central role in the analytical workflow. The feed samples were stored in polyethylene bags in a dry, dark place and then pulverized with cryogenic milling equipment, a step that improves homogeneity and helps ensure that the small aliquots taken for analysis are representative of the bulk material. For the inductively coupled plasma measurements, the samples were digested in a single reaction chamber microwave oven, a design that subjects all vessels to identical pressure and temperature conditions and is well suited to high-throughput laboratories. Residual organic carbon and suspended solids remaining after incomplete digestion are well documented sources of spectral and non-spectral interference in plasma spectrometry, which is precisely the problem that the calibration strategy was designed to overcome.

The instruments used in the study reach very different plasma temperatures, and this difference shapes what each can do. An inductively coupled plasma operates at roughly ten thousand kelvin, while a microwave induced plasma runs at about five thousand kelvin. Both are hot enough to atomize, excite, and ionize many elements, generating the multiple characteristic atomic and ionic emission lines that the multi-energy approach exploits. The microwave induced plasma instrument, which typically uses nitrogen or argon at lower power and gas flow, offers lower operating costs, but its cooler plasma can struggle with more refractory species, making the comparison between the two techniques particularly informative for laboratories deciding which platform suits their needs.

The elements targeted in the study were chosen for their nutritional significance rather than analytical convenience. Calcium, phosphorus, magnesium, sodium, and potassium are macrominerals required in gram quantities and are central to skeletal development, electrolyte balance, and metabolism. Copper, iron, manganese, zinc, and cobalt are trace elements needed in much smaller amounts but still essential for enzyme function, oxygen transport, and immune response. Both deficiencies and excesses of these minerals can cause disease in livestock, and because animal-derived products enter the human food supply, feed mineral content has implications that extend beyond the barn. Feed itself represents roughly seventy percent of pork production costs, so even modest improvements in formulation accuracy carry real economic weight.

The quantitative results illustrate where the calibration strategy delivers its clearest advantages. With the inductively coupled plasma instrument, limits of quantification ranged from 0.09 milligrams per kilogram for manganese up to 31 milligrams per kilogram for calcium and sodium, while the microwave induced plasma method ranged from 0.08 milligrams per kilogram for manganese to 354 milligrams per kilogram for phosphorus. Conventional external calibration produced limits ranging from 0.4 milligrams per kilogram for cobalt to 195 milligrams per kilogram for potassium on the inductively coupled plasma instrument, and from 2.0 milligrams per kilogram for magnesium to 607 milligrams per kilogram for iron on the microwave induced plasma instrument. Recoveries between eighty and one hundred five percent, the range generally accepted as evidence of accurate measurement, were achieved consistently with the multi-energy approach.

The broader context of this calibration strategy helps explain its appeal. Since it was first proposed, the multi-energy concept has been applied across several plasma-based and related techniques, including laser-induced breakdown spectroscopy, which accounts for the largest share of published applications. A survey of the literature shows that publications clustering around these techniques were concentrated in particular years, with a notable peak around 2020, and that comparative studies pairing the two optical emission techniques used here remain limited to a narrow window of prior work. The authors point out that no publications applying the strategy to these plasma techniques appeared in 2022 or 2023, suggesting that the field would benefit from renewed attention and from systematic comparisons of the kind presented in this study.

What distinguishes the approach from other interference-correction options is its diagnostic transparency. Internal standardization and standard addition methods can compensate for matrix effects, but they do not readily reveal which specific wavelengths are compromised. By plotting signals from two solutions against each other across every available emission line, the multi-energy method makes compromised lines visible as outliers that can be identified and excluded, while the remaining lines converge on a reliable concentration estimate. This turns the calibration plot itself into a quality-control artifact that analysts can inspect and archive.

For feed laboratories, the practical appeal is that the method demands only two calibration solutions per sample and requires no modification of existing instrumentation. The sample itself serves as its own matrix match, eliminating the need to prepare matrix-matched standards that mimic the composition of each feed batch. As confined animal production systems expand and the demand for nutritionally balanced feed supplements grows alongside the projected global population, calibration strategies that combine accuracy, simplicity, and compatibility with routine workflows are likely to find increasing application in agricultural and food analysis laboratories.

Subject of Research: Multi-signal calibration for mineral analysis of animal feed by ICP-OES

Article Title: Multi-energy calibration in plasma emission spectrometry: elemental analysis of animal feeds

Article References: Cora Jofre, F., Barros, A. I., Nóbrega, J. A., & Savio, M. (2025). Multi-energy calibration in plasma emission spectrometry: elemental analysis of animal feeds. Frontiers in Analytical Science, 5, Article 1527110. https://doi.org/10.3389/frans.2025.1527110

Image Credits: AI Generated

DOI: 10.3389/frans.2025.1527110

Keywords: animal feed, mineral analysis, plasma spectrometry, calibration, matrix interference, ICP-OES, feed quality control, animal nutrition, Multi-energy, plasma, emission, spectrometry