Determination of Nutritional and Toxic Elements in Food

Agricultural products are crucial for maintaining good health by providing essential nutrients and fibers in daily diets. The agricultural products and resulting foods contain nutritional elements in various concentrations but also elements deemed toxic to humans and/or animals.

Apart from the organically bound elements like hydrogen, carbon, nitrogen, and oxygen, there are more than 30 dietary elements that are needed to ensure the correct functioning of living organisms.

These elements are categorized based on their concentration as macroelements (such as Ca, Mg, Na, K, P, S, Fe, Cu, Zn) with levels above 0.01% and microelements (like Ge, B, Cr, Sn, Zn, F, I, Co, Si, Li, Mn, Cu, Mo, Ni, Se, V, Fe) present in bodily fluids and tissues at less than 0.001%.

The significance of these dietary elements cannot be overstated. They play a crucial role in body composition and various metabolic processes. For instance, calcium is essential for human bones and teeth, blood clotting, and nerve signal transmission.

A calcium deficiency can lead to osteoporosis, metabolic disorders, and other health issues in humans and animals.

Magnesium plays a crucial role in preventing grass tetany in ruminants, while selenium greatly influences cows' fertility. Additionally, a lack of manganese can lead to skeletal deformities in animals and hinder collagen production, affecting wound healing.

However, beyond essential nutrients vital for life, there are harmful elements with detrimental effects on organisms. Examples of such toxic elements include Be, Sb, Bi, Ba, U, Al, Tl, Hg, Cd, and Pb. These toxic elements tend to accumulate in organs like the liver, kidneys, and pancreas.

For instance, cadmium can cause kidney damage and cardiovascular disease. Lead, a highly poisonous metal, adversely impacts nearly every organ and system in the body, particularly affecting the brain and nervous system in children.

Mercury, classified by the World Health Organization (WHO) as one of the top ten toxic chemicals, is also of significant concern.

Mercury exerts toxic effects on various bodily systems, including the nervous, digestive, and immune systems, as well as the lungs, kidneys, skin, and eyes. Exposure primarily occurs through the consumption of fish and shellfish contaminated with methylmercury.

In examining the early stages of our food supply chains, especially in agriculture, it is evident that ensuring livestock receive a balanced diet of macro minerals and trace metals is crucial. This balanced nutrition helps them flourish and stay free from diseases.

Accurate measurement of elemental composition in food and agricultural products is therefore essential for ensuring product safety and maintaining adequate nutritional content.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS), typically used for concentrations ranging from sub-parts-per-billion to high parts-per-million in solution, serves as a vital tool, offering fast, reliable, and routine analysis of samples across a wide concentration range.

This article will discuss the measurement of key elements in food and agricultural reference materials using ICP-MS, which is capable of analyzing traces to major levels within a single analysis.

Materials and Methods

Instrumentation

The analysis was conducted using a PlasmaQuant MS, which features ReflexION ion optics. This patented technology ensures exceptional ion transmission from the interface to the mass analyzer.

Capable of achieving a sensitivity exceeding 500 million c/s per mg/L of analyte (115In), the PlasmaQuant MS maintains oxide ratios (CeO+/Ce+) below 2%. Moreover, it features the patented Integrated Collision Reaction Cell (iCRC) to enable interference-free analysis.

The iCRC mitigates polyatomic ions generated in the plasma, which could otherwise disrupt the determination of elements like As, Se, Cr, V, and Fe, thereby enhancing their detection limits.

Another notable innovation in the PlasmaQuant MS is the All-Digital Detection System (ADD). The system operates in 'pulse-counting' mode, offering an 11-order linear dynamic range. This allows for the routine measurement of elements, spanning from ultra-trace to percentage levels, all within a single analysis.

Utilizing cutting-edge ICP-MS detector technology, the ADD detector system removes the need for analog measurements while preserving the system's maximum dynamic range.

Conditions

The method parameters underwent optimization through the ICP-MS software's Auto-Optimization routine, streamlining the configuration of iCRC, plasma gas flow rates, and ion optic voltages.

Sample Preparation

All samples were accurately prepared by weighing 0.5 g into a microwave vessel. Following this, 10 mL of HNO3 and 1 mL of HCL was added.

The vessel was then heated for 25 minutes and was then maintained at 200 °C for an additional 30 minutes. After cooling to ambient temperature, samples were adjusted to a volume of 20 mL using ultra-pure water (>18 MΩ•cm).

Sample Analysis

Prior to analysis, samples underwent a ten-fold dilution with ultrapure water (>18 MΩ•cm). An internal standard solution was prepared, containing 20 µg/L each of Sc, Y, Rh, Tb, and Lu, and introduced into the sample line via a 'Y piece.' Isotopes were run continuously in normal sensitivity and iCRC mode.

During iCRC mode, hydrogen or helium gas was introduced to the iCRC skimmer cone to mitigate polyatomic interferences. Specifically, hydrogen was utilized for Ca, Fe, and Se, while helium was employed for V, Cr, Cu, Ni, and As. The remaining elements were analyzed in non-iCRC mode.

Calibration

The calibration standards were formulated using high-purity, multielement solutions, with the acid matrix tailored to match that of the samples.

Results and Discussion

A range of different food and agricultural reference materials underwent analysis, such as tea leaves,1 coffee, milk powder,2 bread, kidney, and loam,3 alongside 'intra-laboratory' samples of lime, hay, and animal feed. Table 1 summarizes the results of some of these analyses.

The measured concentrations for each sample generally fell within the certified range or were within ±10% of the certified value, affirming the reliability of the method. Moreover, most results comfortably fell within ±5% of the certified value.

The chosen correction mode was "Interpolated" internal standard correction, which automatically adjusted calibration and sample solution measurements to account for matrix and long-term drift effects.

Table 1. Source: Analytik Jena US

Element Tea leaf Brown bread Silty Clay Loam Hay
Measured Certified Measured Certified Measured Certified Measured Certified
  mg/kg    
23Na 24.0 24.7         0.33% (0.34%)
24Mg     513 500     0.19% (0.21%)
27Al 2145 2290            
31P             0.37% (0.39%)
39K     3128 3100     0.34% (0.35%)
44Ca     422 410     0.54% (0.57%)
51V 1.84 1.97            
52Cr 1.84 1.91 0.077 (0.068-0.360) 41.4 42.4 1.8 (1.9)
55Mn 1540 1570 19.9 20.3 ± 0.7 517 529 79.1 (81.9)
56Fe 423 432 39.0 40.7 ± 2.3     498 (531)
59Co 0.350 0.387     10.1 10.3 0.18 (0.19)
60Ni 6.04 6.12 0.46 (0.44) 28.4 28.8 1.53 (1.61)
65Cu 20.4 20.4 2.6 2.6 ± 0.1 24.8 25.4 7.5 (7.8)
66Zn 34.6 34.7 19.0 19.5 ± 0.5 68.8 69.4 33.0 (34.9)
75As 0.104 0.106 0.024 (0.023) 11.3 11.6 0.27 (0.28)
78Se 0.062 0.076 0.026 (0.025)     0.047 (0.049)
114Cd 0.027 0.03 0.0270 0.0284 ± 0.0014 0.31 0.32 0.079 (0.083)
121Sb 0.046 0.050            
202Hg     0.003 (0.002) 0.091 0.093 0.014 (0.015)
205Tl 0.064 0.063            
206-208Pb 1.56 1.78 0.182 0.187 ± 0.014 24.6 25.2 1.14 (1.19)
238U 0.100 0.099            

Values in brackets are not certified
Range of results observed

Conclusion

This study effectively showcased the capability of the PlasmaQuant MS equipped with iCRC technology and the All-Digital Detection System (ADD10) as a straightforward and efficient solution for directly determining elements across a wide range, from trace to percentage levels, in food and agricultural samples.

This system enabled a single, dependable, and routine analysis. The method's high-throughput nature was demonstrated across various sample types during routine operations.

This was facilitated by swift transitions between iCRC and non-iCRC modes and the innovative detection system, allowing rapid, precise, and accurate measurements across element concentrations ranging from sub-parts-per-trillion to high parts-per-million.

PlasmaQuant MS

PlasmaQuant MS. Image Credit: Analytik Jena US

References

  1. Dybczynski R., Danko B., Kulisa K., Maleszewska E., Polkowska-Motrenko H., Samczynski Z. and Szopa Z. 2004. Preparation and preliminary certification of two new Polish CRMs for inorganic trace analysis. Journal of Radioanalytical and Nuclear Chemistry, 259 (3): 409
  2. Certified Reference Materials 2004, Institute for Reference Materials and Measurements
  3. LGC Standards, Analytical Reference Materials Catalog 2008/2009.

This information has been sourced, reviewed and adapted from materials provided by Analytik Jena US.

For more information on this source, please visit Analytik Jena US.

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