WCPS: Evaluation of sample preparation methods for elemental profiling of wine by ICP-MS: comparison of direct dilution, microwave digestion, and filtration

Importance of the Topic

Elemental profiling of wine by inductively coupled plasma mass spectrometry (ICP-MS) is a critical tool for authentication of origin, monitoring of quality, and regulatory compliance. Wine’s complex organic matrix and suspended particulates present challenges for accurate trace element measurement, making optimized sample preparation a prerequisite for reliable analysis.

Objectives and Study Overview

This study systematically compared four sample preparation approaches for ICP-MS analysis of four wine varieties (Chardonnay, Pinot Noir, Syrah, Tempranillo). The methods evaluated were:

• Direct dilution in nitric acid (DD)
• Acidification before filtration (AF)
• Filtration before acidification (FA)
• Microwave-assisted acid digestion (MW)

Methodology

Each method was applied in triplicate to unrefined wines following centrifugation to remove solids. Calibration employed a six-point external series across 43 isotopes (0.1–500 µg/L) with additional isotope dilution for copper. Quality control included internal standards and periodic calibration checks. Data were evaluated by ANOVA, MANOVA, principal component analysis, and Tukey’s test to assess method effects.

Used Instrumentation

• Agilent 8800x ICP-MS operating with helium collision and high-energy modes
• Milestone UltraWAVE microwave digestion system (240 °C, 150 bar)
• Agilent Captiva Premium PTFE syringe filters (0.45 µm)

Main Results and Discussion

Sample preparation had a statistically significant impact on measured concentrations for 37 isotopes, with the MW method showing the greatest variability and significant differences in 21 isotopes compared to other approaches. Principal component analysis demonstrated that all methods distinguished wine varieties, though MW introduced greater scatter. Limits of detection and blank levels were lowest for MW for some elements but risk of contamination increased with additional steps. Spike recovery experiments for 65Cu and 206Pb indicated comparable performance for most methods, while MW occasionally under-recovered certain isotopes.

Benefits and Practical Applications

• Direct dilution and simple acidification workflows offer rapid turnaround and minimal contamination risk for routine profiling.
• Filtration steps improve matrix removal with moderate complexity and maintain analytical accuracy.
• Microwave digestion achieves complete organic decomposition, beneficial for refractory elements or regulatory methods requiring total digestion.

Future Trends and Potential Applications

Advances may include integration of on-line matrix removal, microfluidic digestion platforms, and coupling with speciation techniques to enhance throughput and data quality. Development of standardized protocols for routine wine authentication and expansion to other beverages will benefit from improved sample prep automation and multivariate calibration strategies.

Conclusion

This comparative assessment highlights the trade-offs among speed, contamination risk, and completeness of digestion. Laboratories should select sample preparation based on target analytes, throughput requirements, and quality criteria, with simple dilution methods sufficient for many applications and microwave digestion reserved for demanding analyses.