High-Throughput, Multi-Element Analysis of Milk and Milk Powder Using ICP-MS

Importance of the Topic

Milk and milk powder are staple foods providing major nutrients and essential trace elements, but they can also accumulate toxic metals through environmental and processing pathways. Rapid, accurate multi-element profiling is critical to ensure both nutritional labeling and food safety compliance for dairy products.

Objectives and Overview of the Study

This study demonstrates a streamlined method for simultaneous determination of major (Na, K, Mg, Ca, P) and trace (Se, Mn, Zn, As, Cd, Hg, Pb, and others) elements in milk and milk powders using a single quadrupole ICP-MS system. Key aims include:

• Developing a single-run analytical protocol that covers ppb to ppm concentrations without changing instrument settings.
• Validating method performance against a certified reference material and applying it to real commercial samples.

Methodology and Instrumentation

Sample Preparation:
Milk powders (0.5 g) and liquid milk (1 g) were digested with HNO₃ and HCl in a closed-vessel microwave system at 240 °C/150 bar. Digests were diluted to 10 mL, then further diluted 1:10 in acid mix for analysis. Triplicate preparations were performed for commercial samples and seven digests for NIST SRM 1549a.

Instrumentation:
An Agilent 7900 ICP-MS equipped with Ultra High Matrix Introduction (UHMI), glass concentric nebulizer, nickel cones, Octopole Reaction System (ORS4) collision cell (He mode), and optional ISIS 3 discrete sampling was used. Preset plasma mode HMI-4 (4× aerosol dilution) simplified operation. Key operating parameters (RF power 1600 W, carrier gas 0.8 L/min, He cell gas 4.3 mL/min) enabled robust performance with 150 s run time per sample.

Calibration and Quality Control:
Twenty-four analytes plus six internal standards were calibrated over appropriate ranges (0–200 000 µg/L for Na, 0–100 000 µg/L for Ca, 0–10 000 µg/L for Mg/P/K/Fe, 0–100 µg/L for Mn/Se/Cu, etc.). A continuing calibration verification (CCV) standard was measured every 10 samples, maintaining recoveries within ±10%.

Key Results and Discussion

Calibration curves exhibited excellent linearity (R² > 0.9998) across wide concentration ranges. Analysis of seven NIST SRM 1549a digests produced recoveries between 97% and 102% with precision typically <3% RSD. Seven commercial milk products were tested for 24 elements; measured levels of major and trace elements agreed with literature values and demonstrated the method’s applicability to diverse matrices.

Benefits and Practical Applications of the Method

• Single-run measurement of both macro- and trace elements without instrument mode changes.
• Expanded eleven-order dynamic range allows ppb to % level determinations together.
• High throughput (150 s per sample) supports routine dairy quality control.
• Robust collision cell interference removal (He mode) ensures accurate low-level detection.
• Preset plasma modes and autotune reduce method development time and operator intervention.

Future Trends and Opportunities

Advances in sample introduction (e.g., flow injection, laser ablation), further CRC chemistries, and integration with automated workflows will continue to enhance throughput and expand capabilities for complex dairy and food matrices. Emerging needs for isotopic analysis and speciation may also leverage this platform with minimal modifications.

Conclusion

The Agilent 7900 ICP-MS combined with UHMI and optional ISIS 3 delivers a robust, sensitive, and high-throughput solution for comprehensive multi-element dairy analysis. Its wide dynamic range, reliable interference control, and simplified operation make it ideal for routine quality assurance, nutritional labeling, and contaminant monitoring in dairy production.

References

1. Khan N, Jeong IS, Hwang IM, Kim JS, Choi SH, Nho EY, Choi JY, Park KS, Kim KS. Multi-element analysis of milk by ICP-MS. Food Chemistry. 2014;147:220–224.