Direct Analysis of Milk Powder by Axially-Viewed Simultaneous ICP-OES

Significance of the Topic

The direct elemental profiling of milk powder is critical for both environmental monitoring of toxic metals and assessment of nutritional constituents. Traditional wet digestion or dry ashing protocols are laborious, time-consuming and employ hazardous reagents. A robust direct analysis approach using inductively coupled plasma-optical emission spectrometry (ICP-OES) streamlines sample preparation and enhances laboratory throughput.

Objectives and Study Overview

This study aimed to develop and validate a simultaneous axially-viewed ICP-OES method for direct quantification of major, minor and trace elements in milk powder suspensions using aqueous calibration standards. Key goals included:

• Correction of viscosity effects via scandium internal standard.
• Suppression of ionization interferences using cesium.
• Measurement of elements ranging from abundant macro-nutrients to toxic trace metals in a single analysis.

Methodology and Used Instrumentation

A Vista simultaneous axial ICP-OES equipped with a 40 MHz RF generator, cooled interface, echelle polychromator and CCD detector was employed. Operating conditions included 1.35 kW power, 15 L/min plasma gas, and 0.6 mL/min sample uptake. Sample preparation involved:

• Creating 2% (w/v) milk powder suspensions in 18 MΩ water with 0.002% Triton X-100 without acid to prevent protein precipitation.
• Sonication and magnetic stirring to maintain homogeneity.
• Online addition of 1% CsCl with 0.5 mg/L Sc via a three-channel peristaltic pump for ionization suppression and viscosity correction.

Main Findings and Discussion

• Analysis of NIST SRM 8435 yielded element concentrations in close agreement with certified values (e.g., Ca: 8990 ± 340 vs 9220 ± 490 ppm, Zn: 25.2 ± 0.9 vs 28.0 ± 3.1 ppm), validating method accuracy.
• MAF sample results demonstrated reliable quantification of Ba, Ca, K, Fe, Mn, Na, P, S, Sr and Zn in a single run.
• Selection of less sensitive emission lines and axial viewing avoided the need for dilution or separate optical configurations.

Benefits and Practical Applications

• Elimination of hazardous digestion steps reduces analysis time and risk.
• Simultaneous detection across a wide dynamic range supports QA/QC in dairy, nutrition and environmental laboratories.
• Internal standard correction ensures high precision and reproducibility.

Future Trends and Potential Uses

• Integration with automated sample introduction systems for high-throughput screening.
• Extension to other complex matrices such as plant powders or food supplements.
• Coupling with mass spectrometry detection for isotope-specific or ultra-trace analysis.
• Development of miniature or portable ICP-OES for field-based testing.

Conclusion

The axially-viewed simultaneous ICP-OES method enables direct, accurate and efficient multi-element analysis of milk powder without chemical digestion. Corrections for viscosity and ionization effects using Sc and Cs internal standards ensure data quality across major nutrients and trace contaminants.

Reference

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