Analysis of Food and Agricultural Samples Using the aurora M90 ICP-MS with Collision Reaction Interface (CRI)

By AZoM

Table of Contents

Introduction

Trace amounts to percentage levels of multiple concentrations of nutrients can be found in foods and agricultural products. While most of the nutrients are essential to maintaining human health, the concentrations of these elements can compromise the benefits of the essential mineral content by becoming toxic to humans and/or animals. Studies have been done to understand the health impacts of dietary exposure to varying levels of metals and minerals for humans.

Division of Inorganic Elements Based on Studies

The inorganic elements are categorized into four groups based upon the concentrations at which deficiencies and toxicities can be observed-

• Macrominerals – Large quantities of P, K, Mg, Na, S, Fe, Cu, Ca and Zn are required to be consumed for nourishment and support of life.
• Essential trace minerals – Small quantities of B, Mn, Cr, Br, Si, I, V, Li, Se, Ge, Mo, Co, and others provides good health.
• Possibly required trace minerals – Some studies propose the human body’s requirement for other elements, for example, F, As, Rb, Sn, Nb, Sr, Au, Ag, and Ni.
• Toxic metals – Dietary intake of these deleterious elements should be minimized, for example, Be, Hg, Pb, Cd, Al, Sb, Bi, Ba, and U.

Some of today’s medical conditions (such as hypothyroidism, diabetes, and cancer) are attributed to the extent of exposure to toxic metals in the modern diet. It has also been noted that correct balance of macrominerals and trace metals in livestock feed helps the animals to thrive and be disease free.

Examples from the Agricultural industry

Certain examples from the Agricultural sector include the following:

• Cobalt supplements are often used for enhancing the well-being of sheep
• Magnesium supplements for ruminants are known to prevent grass tetany
• Selenium has been proved to enhance the fertility of cows

Precise measurement of elemental composition in food and agricultural products is higly important in ensuring product safety and maintaining proper levels of nutritional content. The concentrations range from sub parts per- billion to high parts-per-million in solution.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

The ICP-MS is an important tool for performing quick, accurate and routine analysis of samples in a large concentration range. The measurement of key elements in food and agricultural sample materials from trace to major levels are examined for the purpose of this application note by utilizing the ICP-MS within a single analysis.

Instrumentation

The aurora M90 is an ICP-MS model that features:

• Patented 90-degree ion mirror- provides unique transmission of ions from the interface to the mass analyzer
• Can achieve excellent sensitivity that exceeds 1000 million c/s per mg/L of analyte while being able to maintain the oxide ratios (CeO⁺/Ce⁺) below 3%.
• Comprises the patented Collision Reaction Interface (CRI) interference management System that attenuates polyatomic ions found in the plasma, which can interfere with the determination of elements, such as Se, As, V, Cr and Fe, thus improving their detection limits
• Comprises completely digitized, discrete dynode electron multiplier (DDEM) detection system, which provides nine orders (10⁹) of linear dynamic range in only one mode i.e. ‘pulse-counting’ mode, thus ensuring routine measurement of elements from ultra trace to percentage levels within a single analysis.
• Linearity of the DDEM is advantageous to achieve an equivalent dynamic range.
• Dual-mode detectors- when the ion signal is very strong, the detector will have to switch to an analog measurement mode that extends further three orders. For operating across the same concentration range, the dual-mode detector has to employ a complex and inaccurate cross-calibration to bridge the separation in linearity that happens while switching between its disparate modes. Cross-calibrations are inconvenient but by using the ICP-MS detector technology in the DDEM, the need for analog measurements is not required while maintaining maximum dynamic range.
• Three attenuation modes of none, medium, and high are available and can be automatically set for each element during the sample analysis. This enables isotope ratios and element concentrations from sub parts-per-trillion to high parts-per-million to be correctly measured in pulse-counting mode only.

Conditions

The operating parameters are represented in Table 1. The method parameters were formulated using Automax routine of the ICP-MS software, which automates setting of the CRI and plasma gas flow rates and ion optic voltages.

Table 1. aurora M90 ICP-MS instrument operating parameters

Sample Preparation

By accurately weighing about 0.5 g of the sample into a microwave vessel into which 10 mL of HNO₃ and 1 mL HCl were later included, thus the sample was prepared. Next the vessel was heated for 25 min. and held at 200 °C for another 30 min. Samples were cooled to ambient temperature and made up to 20.00 mL using ultra-pure water (>18 MW•cm).

Sample Analysis

The samples were diluted ten-fold with ultrapure water (>18 MW•cm) before the analysis. An internal standard solution was prepared with 20 mg/L of 45Sc, 89Y, 103Rh, 159Tb, and 175Lu, which was added online to the sample line via a ‘Y piece’. Isotopes were operated in regular sensitivity mode and CRI mode in one continuous method. When operating in the CRI mode, helium or hydrogen gas was added to the CRI skimmer cone to attenuate all polyatomic interferences. Hydrogen was used for elements Fe, Se, Ca and helium for Ni, V, Cr, Cu, and As. Non CRI mode was used the other remaining elements.

Calibration

Calibration standards were established from highly pure, multi-element solutions and acid matrix matched to the samples.

Results and Discussion

A wide range of food and agricultural sample materials, such as, bread, tea leaves, coffee, milk powder, kidney, bread, and loam, and intra-laboratory samples such as hay, lime, and animal feed were studied. The results are summarized in Tables 2–10, where Tables 2–6 provide the results obtained for five different food samples. Measured concentrations for each of the samples were typically within the certified range or }10% of the certified value, thus affirming the validity of the method.

Table 2. Results for tea leaf reference material INCT-TL-1

Table 3. Results for skim milk powder reference material BCR-150

Table 4. Results for pig kidney reference material BCR-186

Table 5. Results for brown bread reference material BCR-191

Table 6. Results for coffee powder reference material T0759 (FAPAS)

Table 7. Results for Silty Clay Loam reference material CRI7003 (aqua regia soluble)

Table 8. Results for Lime intra-laboratory reference material

Table 9. Results for Feedstuff intra-laboratory reference material

Table 10. Results for Hay intra-laboratory reference material

Conclusion

This application work has productively explained that the aurora M90 ICP-MS along with the CRI technology can provide a simple but effective solution for the direct determination of elements from trace to percentage levels in food and agricultural samples within a single and reliable analysis.

About Bruker

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• Gas Chromatography-Mass Spectrometers (GC/MS and GC/MS/MS)
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