Simple, Rapid Analysis of Trace Metals in Foods Using the Agilent 7700x ICP-MS

INTRODUCTION

The task of efficiently monitoring chemical and biological contaminants in imported and exported food can be overwhelming. Traditionally, analysis of metals in foods has required multiple techniques in order to cover the range of elements, concentrations, and food types. This approach is slow and expensive, so a more rapid, sensitive, and cost-effective screening test is necessary. The Agilent 7700x ICP-MS is capable of accurately analyzing a variety of foods for metals at trace and major levels using a single collision cell method. This method is simple to set up and operate routinely, and permits large numbers of samples to be quickly screened for total toxic metals. Samples that are found to contain metals where the potential toxicity is dependent on the chemical form can then be further analyzed for species composition as needed, using Agilent-supported hyphenated ICP-MS techniques such as LC-ICP-MS or GC-ICP-MS.

EXPERIMENTAL

To test the ability of the Agilent 7700x to analyze a variety of foods for a wide range of metals at highly variable concentrations, several certified reference food samples were analyzed. The 7700x was tuned using One-Click Plasma setting for robust plasma conditions and autotuned for optimum sensitivity, mass response, and minimal interferences. Operating conditions are shown in Table 1. To keep the method as quick and simple as possible, the Octopole Reaction System (ORS³) was operated in a single mode, using helium (He) cell gas, which provides a reliable and effective cell method to remove all polyatomic interferences, regardless of the analyte or matrix composition. The following acquisition masses and integration times (Table 2) provided more than sufficient sensitivity to meet all certified values. Total run time per sample was less than 3 minutes.

Table 1. 7700 Autotuning Conditions

Traditionally, covering this range of concentrations for these elements would have required ICP-OES for the major elements (Na and Ca), graphite furnace AA for Pb and Cd, either a dedicated Hg analyzer or cold vapor AA for Hg and possibly hydride AA for As and Se. The Agilent 7700x ICP-MS running in He mode was able to measure all elements in a single run easily. Even elements such as Be and Hg, which would typically be acquired under no-gas conditions when using ICP-MS, demonstrated excellent sensitivity in He mode (Be DL = 28 ppt, Hg DL = 1.6 ppt).

Table 2. List of analytes and acquisition times (All elements were acquired in He mode)

Example calibration curves for several critical and difficult elements are shown in Figure 1.

Figure 1. Calibrations for Be, Cr, As, Se, Cd, and Hg.

The food certi. ed reference materials were analyzed directly after microwave digestion. Between 0.5 g and 1 g of each sample was weighed (after determination of percent moisture) and digested using 6 mL of HNO₃ + 2 mL of H₂O₂ using microwave assisted digestion. All samples were brought to . nal volume of 100 mL using ultrapure water. Results are shown in Table 3. The trace elements, Ni, Mn, Cu, As, Se, Cd, Hg, and Pb exhibited excellent agreement with the certi. ed values for all three samples. Slight deviations from certi. ed values for Fe, Ca, and Zn were attributed to the digestion procedure rather than the analytical measurement.

Table 3. Measured and certified values for three certified reference food materials. Recoveries are dependent on digestion efficiency as well as analytical accuracy. All measured values are based on dry sample weight corrected for percent moisture. All certified elements are reported for each sample; not all samples are certified for all elements

CONCLUSIONS

Using a simple procedure based on microwave digestion and single He mode ICP-MS analysis, typical food samples can be quickly and accurately analyzed for trace and major element concentrations without the need for multiple sample preparations and analytical techniques. The Agilent 7700x using He mode alone can provide sensitive, accurate, interference-free analysis of a variety of metals in common foods. Because He mode is both sensitive and universal, it is applicable to trace analysis of all metals in any food sample digest. No prior information about the sample matrix or analyte elements present is required, as He mode removes all polyatomic interferences, regardless of the sample matrix.

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