Measurement of Trace Elements in Malt Spirit Beverages (Whisky) by 7500cx ICP-MS

Importance of the topic

The control of trace metals in distilled beverages is critical both for safeguarding product quality and meeting regulatory standards. Elements may enter spirits via raw materials, processing equipment or storage containers, influencing both safety and flavor. An analytical method that offers low detection limits, robust interference removal, and reliable quantification supports routine quality assurance in the beverage industry.

Objectives and overview

This study evaluated a unified procedure for quantifying trace elements in six malt whisky samples using an Agilent 7500cx ICP-MS with the Octopole Reaction System (ORS). Key aims included assessing interference suppression under different cell gas modes, verifying method precision and accuracy through spike recoveries, and demonstrating suitability for routine beverage analysis.

Methodology and instrumentation

Sample Preparation:

• Six whisky types (Scottish Highland, Speyside, Islay, blended, one Irish, one U.S. bourbon; two stored in lead crystal decanters) were diluted fivefold in an acid mixture of 1% HNO₃ and 0.5% HCl with 8% ethanol to mirror alcohol content in calibration standards.
• Gold (400 µg/L) and internal standards (Ge, Rh, Ir) were added online to stabilize mercury and correct for signal drift.

Instrumentation:

• Agilent 7500cx ICP-MS with ORS collision/reaction cell.
• Cell gas modes: helium for polyatomic interference removal; hydrogen for enhanced selenium detection at sub-ppt levels.
• Spray chamber cooled to 15 °C, sample uptake ~150 µL/min, RF power 1550 W.
• Autosampler: Agilent ASX-520; multi-rinse protocol used to minimize carry-over.

Main results and discussion

Interference Suppression and Detection Limits:

• Switching from no-gas to helium mode reduced background equivalent concentrations (BECs) dramatically (e.g., 52Cr BEC from 526 µg/L to 0.07 µg/L), restoring accurate quantification in this carbon- and chloride-rich matrix.
• Hydrogen mode further improved arsenic and selenium detection, lowering Se BEC from ~1.4 µg/L (no gas) to 0.013 µg/L.

Precision and Accuracy:

• Five-hour stability test on a spiked Highland sample (54 measurements) yielded < 2% RSD for almost all analytes, confirming long-term stability.
• Spike recoveries in Islay whisky ranged from 97% to 107%, demonstrating method accuracy.

Sample Composition Insights:

• Common whisky elements (Fe, Mn, Cr, Cu, Zn) were quantified with high sensitivity.
• Samples stored in lead crystal decanters contained nearly tenfold higher Pb (≈10 µg/L) compared to those in glass, highlighting storage impact.

Benefits and practical applications

The approach offers a single, simplified workflow for diverse spirits, removing the need for multiple methods or frequent re-optimization. Consistent cell conditions allow broad elemental coverage and semiquantitative screening in full-scan helium mode, speeding routine QA/QC testing in distilleries and regulatory labs.

Future trends and possibilities

Continued integration of collision/reaction cell technology may extend analysis to emerging contaminants and ultra-trace species. Advances in automation and data handling will streamline high-throughput beverage screening. Adapting this methodology to other complex matrices (e.g., cocktails, hard seltzers) can broaden its industrial relevance.

Conclusion

The Agilent 7500cx ICP-MS with ORS delivers reliable, interference-free quantification of trace metals in high-alcohol matrices after minimal sample prep. Helium mode effectively removes polyatomic overlaps, while hydrogen mode boosts low-ppt selenium detection. Robust precision, excellent recoveries, and a unified operating procedure support its routine application in beverage quality control.

References

1. Achieving Optimum Throughput in ICP-MS Analysis of Environmental Samples with the Agilent 7500ce ICP-MS, Agilent ICP-MS Journal 27, 2006, 5989-5132EN.