Rapid Determination of Seven Elements in Milk Powder by Microwave Digestion and Flame Atomic Absorption Spectrometry

Significance of the Topic

Milk powder is a key source of essential nutrients for infants and adults. Accurate quantification of macroelements (K, Na, Ca, Mg) and trace elements (Fe, Zn, Cu) in dairy products is crucial for nutritional labeling, quality control, and regulatory compliance.

Study Objectives and Overview

This study demonstrates a rapid and efficient workflow for the simultaneous determination of seven elements in milk powder using microwave digestion combined with Fast Sequential Flame Atomic Absorption Spectrometry (FAAS) on an Agilent 280FS instrument. The approach aims to reduce analysis time, gas consumption, and potential errors associated with multiple sample aspirations.

Methodology and Instrumentation

• Sample Preparation and Digestion: 0.500 g of milk powder digested in 5 mL of nitric acid via a three-step accelerated microwave program, followed by evaporation and dilution to 50 mL with lanthanum oxide addition.
• Instrument Setup: Analysis on Agilent 280FS FAAS equipped with seven single-element hollow cathode lamps (K, Na, Ca, Mg, Fe, Zn, Cu) operating in Fast Sequential mode.
• Fast Sequential Mode: Simultaneous lamp operation with rapid mirror and wavelength switching, enabling measurement of all elements from a single flame aspiration.
• Calibration: Five-point external calibration for each element (0.05–0.80 mg/L for alkali metals, up to 8 mg/L for alkaline earth and transition metals) yielded correlation coefficients above 0.9987.

Main Results and Discussion

The method achieved high linearity with r2 > 0.9987 for all elements. Precision and accuracy were evaluated via six replicates of a certified milk powder reference: recoveries ranged from 90 to 102% and RSDs were below 2.5% (except Ca at 3.7%), demonstrating robust performance for routine quality control.

Benefits and Practical Applications

• Reduced analysis time by fourfold compared to conventional FAAS.
• Lower acetylene and air consumption due to single-sample aspiration.
• Minimized operator interventions and potential sample handling errors.
• Cost-effective solution for laboratories conducting multi-element nutritional analysis.

Future Trends and Potential Applications

Advancements in fast sequential atomic absorption and integration with automated sample preparation promise further throughput gains. Expansion to additional food matrices, coupling with other detection techniques, and adaptation to inline monitoring in dairy processing are potential directions.

Conclusion

The combined microwave digestion and Fast Sequential FAAS method on the Agilent 280FS offers a rapid, accurate, and economical approach for multi-element determination in milk powder. Its high precision and simplicity make it suitable for routine food testing laboratories.

References

1. Li Y., Siqi W., Junjie G., Chengcheng P., Rapid Determination of Seven Elements in Milk Powder by Microwave Digestion and Flame Atomic Absorption Spectrometry, Agilent Technologies Application Brief, May 2021.