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

The importance of molecular weight is not trivial. The bioactivity of collagen and elastin peptides, their absorption in the gut, and ultimately their claimed effects on skin hydration, elasticity and photoaging all depend heavily on the size of the peptide fractions. Smaller peptides, particularly those below 1 kilodalton, are generally considered the most bioavailable and biologically active. Previous work by the same research group had already shown that a collagen peptide beverage maintained a stable distribution during three months of accelerated storage, with more than 65 percent of peptides below 1 kDa and antioxidant activity, measured by ABTS radical scavenging, preserved at 80 to 90 percent. But existing national and industry standards for molecular weight determination were written for simple peptide powders, not for multi-ingredient beverages.

Leading the study, researchers from China compared three mainstream gel permeation chromatography methods drawn from Chinese national and enterprise standards, designated Methods A, B and C, each using a different acetonitrile-water-trifluoroacetic acid mobile phase composition. All three relied on the same TSK-GEL G2000 SWXL size-exclusion column, UV detection at 220 nanometers, and calibration with a suite of peptide standards ranging from cytochrome C at 12,384 daltons down to glycylglycylglycine at just 189 daltons. The team tested the methods on a pure collagen and elastin peptide powder and on two commercial beverages, one fortified with vitamin C and one with epigallocatechin gallate, both made from the same production batches of peptide raw material, allowing a rigorous like-for-like comparison.

The first major finding concerned calibration curve fitting, a detail with outsized consequences. Gel permeation chromatography estimates molecular weight from retention time via a calibration curve, and the researchers showed that the relationship between the logarithm of molecular weight and retention time is inherently sigmoidal rather than linear, consistent with established theory in size-exclusion chromatography. Linear fits produced coefficients of determination between 0.9898 and 0.9925 but left systematic U-shaped residual patterns, revealing hidden bias. Refitting with cubic polynomials raised the R-squared values to between 0.9970 and 0.9999 and slashed the root mean square error, with Method B achieving an extraordinary R-squared of 0.9999 and residuals within ±0.01. In short, the mathematical model used to process the data mattered as much as the chromatography itself.

Repeatability was another pillar of validation. Standard samples re-injected before and after each batch showed retention time relative standard deviations below 0.1 percent, and theoretical plate numbers for the smallest standard exceeded system suitability requirements across all methods, confirming that the column remained in good condition. When the researchers calculated the distribution across five molecular weight ranges and three average molecular weight parameters, the RSD values for all samples stayed below 3 percent under both fitting models, demonstrating that each of the three methods is internally precise and suitable for the comparative analysis that followed.

The most commercially significant breakthrough, however, was the solution to matrix interference. In principle, any peak eluting after the smallest peptide standard, around 20.5 minutes, must represent compounds smaller than 189 daltons. The team hypothesized that this late-eluting region might instead contain aromatic beverage excipients absorbing UV light. Testing pure vitamin C and EGCG under identical conditions confirmed it: both additives eluted after the 20.5-minute cutoff, and the apparent sub-189 dalton fraction swelled to as much as 20 percent of the total distribution in the beverages. By simply excluding peaks after 20.5 minutes, the researchers eliminated the interference entirely. After the cutoff was applied, chromatographic profiles of powder and beverages overlapped almost perfectly, all relative deviations fell below 10 percent, and chromatographic fingerprint similarity analysis using the system recommended by the Chinese Pharmacopeia Commission returned correlation coefficients above 0.99 between each beverage and the pure peptide reference.

With interference removed, the study turned to the question of whether different laboratories using different official methods could ever agree on a number. Under linear fitting, significant differences appeared among the methods, particularly in the high molecular weight range above 3 kDa and in key parameters such as the weight-average molecular weight, whose ranking even flipped depending on the fitting model. Under cubic fitting, those systematic discrepancies largely vanished. In the critical sub-1 kDa region, where bioactive small peptides concentrate, all three methods became statistically consistent, with inter-method RSD values below 5 percent. The authors propose that if the industry adopts cubic polynomial fitting as a shared data-processing convention, results from different platforms become directly comparable; failing that, Method A, which proved most robust across both fitting modes, could serve as an interim reference method.

Perhaps the most reassuring result for product developers is that formulation freedom and analytical rigor can coexist. The two beverages deliberately contained ingredients chosen to adjust pH, viscosity, flavor and stability, including sodium hyaluronate, chitosan oligosaccharide and broccoli seed extract in the EGCG formulation. Electronic nose and electronic tongue profiling confirmed that the drinks delivered noticeably richer, more balanced flavor profiles than the plain peptide powder, with more harmonious distributions of umami, saltiness, sweetness and sourness. Crucially, none of this sensory engineering disturbed the measured molecular weight profile of the peptides. Manufacturers can therefore optimize taste, mouthfeel and shelf life without compromising the verifiable quality of the functional ingredient, provided the 20.5-minute exclusion rule and appropriate fitting model are applied.

The authors are candid about limitations. All experiments ran on a single HPLC platform, so cross-instrument validation remains to be done, and the exclusion rule has so far been tested only in these two matrices, with spiking recovery or blank matrix runs recommended for unknown formulations. The TSK-GEL G2000 SWXL column also has limited resolution below 500 daltons, where a difference of one or two amino acid residues barely changes hydrodynamic volume; the authors suggest LC-MS/MS or dedicated small-molecule columns such as Superdex 30 Increase for fine characterization in that range, and point toward future work linking precise peptide spectra to in vitro bioactivity and clinical endpoints. Even so, the framework delivers three concrete contributions: a validated chromatographic cutoff to strip away non-peptide interference, clear evidence that cubic fitting slashes inter-method variability, and demonstration that the approach survives contact with real, commercially formulated products. For an industry racing to capitalize on collagen’s popularity, that combination of rigor and practicality may prove as valuable as the peptides themselves.

Subject of Research: Molecular weight analysis of fish-derived collagen peptides in beverages by comparative gel permeation chromatography

Article Title: Developing an Analytical Framework for the Molecular Weight Analysis of Fish‐Derived Collagen Peptides in Beverages: A Multi‐Method Comparative Study

Article References: Feng, M., Li, Y., Luo, Y., Jiang, Y., & Zhao, C. (2026). Developing an Analytical Framework for the Molecular Weight Analysis of Fish‐Derived Collagen Peptides in Beverages: A Multi‐Method Comparative Study. Food Science & Nutrition, 14(9), Article e72386. https://doi.org/10.1002/fsn3.72386

Image Credits: AI Generated

DOI: 10.1002/fsn3.72386

Keywords: collagen peptides, gel permeation chromatography, molecular weight distribution, functional beverages, fish-derived peptides, matrix interference, calibration curve fitting, quality control, elastin peptides, food analysis, skin health, HPLC

The research, led by Anoja N of the National Water Supply and Drainage Board in Sri Lanka, together with R. C. L. De Silva of the University of Kelaniya and J. Prabagar of the University of Jaffna, was driven by a pressing regional and global problem. Coastal waters in northern Sri Lanka carry total dissolved solids (TDS) of approximately 39,400 milligrams per liter, while hypersaline brines in the same region exceed 56,000 milligrams per liter — far above the roughly 35,000 milligrams per liter of natural seawater. With desalination facilities expanding worldwide to combat freshwater scarcity, the concentrated brines they discharge, laden with sodium, chloride, magnesium, and trace metals such as cadmium, lead, and zinc, represent a growing environmental concern. Monitoring these waters for toxic metals is essential, but conventional analytical methods buckle under the extreme salinity.

The analytical difficulty is rooted in what chemists call matrix interference. In a graphite furnace atomic absorption spectrometer, a small volume of sample is dried, pyrolyzed, and finally atomized at high temperature inside a small graphite tube, and the absorption of light by free cadmium atoms is measured at a characteristic wavelength of 228.8 nanometers. The problem is that when the sample contains enormous quantities of dissolved salts, those salts produce their own nonspecific absorption and physical effects that scatter or suppress the analyte signal. In conventional measurements without correction, blank artificial seawater produced an apparent cadmium concentration of 41.88 micrograms per liter — a massive phantom signal — while blank artificial brine yielded 54.18 micrograms per liter. Without intervention, such readings would be catastrophically misleading.

The Sri Lankan team attacked the problem on two fronts. First, they exploited the three-field Zeeman background correction system of their Analytik Jena ZEEnit 700P instrument, which uses a magnetic field to separate the true atomic absorption signal from nonspecific background absorption. The effect was striking. With Zeeman correction applied, the apparent cadmium in blank artificial seawater plummeted from 41.88 to 0.92 micrograms per liter, and in blank artificial brine from 54.18 to 0.24 micrograms per liter. For samples spiked with 10 micrograms per liter of cadmium, measured values dropped from 39.45 to 8.48 micrograms per liter in seawater and from 52.78 to 6.78 micrograms per liter in brine. The second front was the optimization of the graphite furnace temperature program itself — the sequence of drying, pyrolysis, and atomization steps that determines how cleanly the salty matrix is driven off before cadmium atoms are measured.

Using a one-variable-at-a-time approach, the researchers systematically explored drying temperatures of 110, 150, and 200 degrees Celsius; pyrolysis temperatures from 700 to 1000 degrees Celsius; and atomization temperatures from 1200 to 1600 degrees Celsius. For artificial seawater, the sweet spot proved to be drying at 150 degrees Celsius, pyrolysis at 800 degrees Celsius, and atomization at 1400 degrees Celsius. The pyrolysis step is the critical one: it must be hot enough to vaporize the salt matrix but not so hot that volatile cadmium is lost. Above 800 degrees Celsius, cadmium signals declined, evidence of analyte volatilization. For the far more concentrated artificial brine, everything remained the same except the atomization temperature, which needed to rise to 1500 degrees Celsius to achieve maximum absorbance and excellent precision, with a relative standard deviation of just one percent. Three distinct furnace programs emerged: a manufacturer default for clean standards and certified reference materials, and matrix-specific programs tuned for seawater and hypersaline brine respectively.

The payoff of this matrix-specific tuning was dramatic in the recovery studies. When the default furnace program was used both to calibrate and to measure cadmium in seawater, salt-induced signal suppression crushed recoveries to a mere 5 to 26 percent — essentially useless. But when aqueous calibration was paired with measurement under the optimized seawater program, recoveries jumped to between 85 and 107 percent in both undiluted and diluted samples. Hypersaline brine, with its stronger suppression, required an additional step: simple dilution. Undiluted brine analyzed with the optimized brine program yielded recoveries of 83.8 to 92.9 percent, and after two-fold dilution the recoveries reached 94.1 to 95.1 percent. Notably, the study found that cadmium recovery correlates strongly and inversely with electrical conductivity, a practical indicator that higher ionic strength intensifies matrix interference.

Calibration strategy mattered as much as furnace chemistry. External calibration with aqueous standards delivered excellent linearity, with coefficients of determination exceeding 0.999, and precision improved as cadmium concentrations rose, with the relative standard deviation falling from 7 percent at 2.5 micrograms per liter to 2 percent at 10 micrograms per liter. Matrix-matched calibration, though superficially linear, systematically overestimated cadmium — a signal enhancement bias that ruled it out for routine work. The standard addition method, in which samples are spiked incrementally, performed best of all, with a coefficient of determination of 0.9995 and a recovery of 92.7 percent for a fortified seawater sample measured at 0.93 micrograms per liter, confirming negligible residual matrix effects even at ultra-trace levels.

The method’s sensitivity and reliability were rigorously quantified. The limit of detection was 0.50 micrograms per liter in ultrapure water, 0.76 micrograms per liter in artificial seawater, and 0.59 micrograms per liter in artificial brine — comfortably below the concentrations of environmental concern. Measurement uncertainty, evaluated under the EURACHEM/CITAC framework by accounting for standard preparation, calibration, repeatability, and recovery bias, produced a combined standard uncertainty of 0.31 micrograms per liter and an expanded uncertainty of plus or minus 0.62 micrograms per liter at a 95 percent confidence level. The dominant contributor was day-to-day analytical repeatability rather than any systematic bias, and the fortified seawater sample measured 10.16 plus or minus 0.62 micrograms per liter — comfortably within the generally accepted plus-or-minus 10 percent performance criteria for trace metal analysis in complex matrices.

What makes the study especially timely is its explicit embrace of Green Analytical Chemistry. Traditional approaches to taming salt matrices — solid-phase extraction, dispersive liquid-liquid microextraction, cloud point extraction — consume hazardous organic solvents, generate chemical waste, and demand laborious sample preparation. Even greener alternatives such as deep eutectic solvents struggle under the extreme salinity of hypersaline brine. The new method sidesteps all of this: it requires no chemical modifier at all, uses just 20 microliters of sample per analysis, relies on ultrapure water and dilute nitric acid, and completes each determination in roughly two to three minutes. A formal assessment using the Green Analytical Procedure Index (GAPI) classified 13 of 15 evaluation criteria as green, reflecting low reagent consumption, minimal waste, and reduced handling risk. Even the graphite tubes proved durable, surviving approximately 543 analytical cycles and minimizing solid waste.

The authors are careful to note that further validation with natural seawater samples from different geographical locations would strengthen the method’s broader applicability, and the instrument’s instantaneous energy demands are higher than those of low-energy extraction techniques — though the short atomization cycle keeps total energy use modest. Still, the study demonstrates something analytically satisfying: that a conventional, widely available instrument can be coaxed into reliable performance in one of the harshest sample matrices in environmental chemistry simply by understanding and exploiting the volatility differences between the salt matrix and the analyte. As desalination expands across water-stressed coastlines worldwide, this modifier-free, Zeeman-corrected approach offers monitoring laboratories a practical, sustainable route to safeguarding marine waters against cadmium contamination — no exotic reagents required.

The findings carry practical weight for environmental regulators. Cadmium is listed by the World Health Organization and national agencies as a priority pollutant, and drinking water guidelines typically sit in the low microgram-per-liter range, so a detection limit of 0.76 micrograms per liter in seawater places the method squarely within the sensitivity window needed for compliance monitoring. Because the procedure relies on equipment already installed in many water quality laboratories, adoption barriers are low compared with techniques requiring dedicated inductively coupled plasma instrumentation.

The study also illustrates a broader trend in analytical chemistry: rather than adding complexity to overcome interferences, careful exploitation of fundamental chemistry — here, the volatility gap between a chloride-rich salt matrix and a relatively volatile metal — can achieve cleaner results with fewer reagents. The one-variable-at-a-time optimization strategy, though simpler than modern multivariate designs, proved sufficient to isolate the critical temperature thresholds, and the confirmation experiments demonstrated that the resulting furnace programs were robust across repeated cycles.

Alignment with the United Nations Sustainable Development Goals on responsible consumption and life below water underscores the motivation. As brine discharges intensify in arid coastal regions, routine, low-waste monitoring of trace metals becomes a necessity rather than an aspiration. Extending the validated approach to other trace metals such as lead and zinc, and to natural field samples across diverse oceanographic settings, represents the logical next step for this line of research.

Subject of Research: A modifier-free, Zeeman-corrected GFAAS method for trace cadmium determination in seawater and hypersaline brine

Article Title: Environmentally sustainable modifier-free, Zeeman-corrected graphite furnace atomic absorption spectrometry for trace cadmium determination in seawater and hypersaline brine

Article References: N, A., De Silva, R. C. L., & Prabagar, J. (2026). Environmentally sustainable modifier-free, Zeeman-corrected graphite furnace atomic absorption spectrometry for trace cadmium determination in seawater and hypersaline brine. BMC Environmental Science, 3(1), Article 20. https://doi.org/10.1186/s44329-026-00062-w

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00062-w

Keywords: cadmium, graphite furnace atomic absorption spectrometry, seawater, hypersaline brine, matrix interference, Zeeman background correction, green analytical chemistry, desalination brine, GAPI, trace metal analysis, measurement uncertainty, environmental monitoring