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Silver Chloride Precipitation-limiting Factor for Accurate Silver Determination in Ag-accumulating Mushrooms After Nitric Acid Digestion

Summary

This research addresses a critical problem in measuring silver content in certain mushrooms, particularly silver-accumulating Amanita species. Scientists discovered that standard laboratory digestion procedures using nitric acid can cause silver to precipitate as silver chloride, making it invisible to measurement instruments and leading to false low results. The study demonstrates that neutron activation analysis is more accurate for measuring silver in these mushrooms, or alternatively, specialized multi-step digestion procedures can dissolve the precipitated silver chloride to obtain accurate measurements.

Background

Wild-growing mushrooms are capable of accumulating high amounts of trace elements including noble metals. Previous studies using INAA reported high silver concentrations in Amanita strobiliformis, but subsequent ICP-MS analyses after HNO3 digestion yielded unexpectedly low values, suggesting a potential analytical problem.

Objective

This study aimed to investigate the discrepancy between non-destructive INAA and destructive HR-ICP-MS methods for silver determination in mushroom samples, particularly Ag-hyperaccumulating species. The authors hypothesized that insoluble silver chloride precipitation during nitric acid digestion could explain the low ICP-MS results in samples with high chloride content.

Results

Results revealed significant discrepancies between INAA and HR-ICP-MS methods in samples with high both silver and chloride content, with recoveries as low as 2-45%. Ag-spiking experiments confirmed dramatically decreased recovery with increasing silver additions in chloride-rich samples. SEM and XRD analysis unambiguously identified the precipitate as silver chloride crystals.

Conclusion

Silver determination in mushrooms using standard acid digestion procedures is problematic in samples with high silver and chloride content due to AgCl precipitation. INAA is the most suitable method for accurate Ag determination in mushrooms, or alternatively, specialized multi-step digestion procedures that dissolve precipitated AgCl before measurement.
  • Published in:Biological Trace Element Research,
  • Study Type:Analytical Methodology Study,
  • Source: PMID: 40227466, DOI: 10.1007/s12011-025-04605-1
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