Simultaneous Determination of Lead, Total Arsenic, and Total Mercury in Table Salt Using Three-Channel Atomic Fluorescence Spectroscopy

Literature Overview

This paper by Liu Baolan, Lv Xiaodong, Yao Heng, Wang Mengmeng, and He Jutao, published in Chemical Analysis and Metering in 2026 (Vol. 35, No. 3, pp. 33-40), describes the development and validation of a three-channel atomic fluorescence spectrometry (AFS) method for the simultaneous determination of lead (Pb), total arsenic (As), and total mercury (Hg) in edible salt. The research was supported by the Science and Technology Program of the Henan Provincial Administration for Market Regulation (Project No. HNSCJK202564). The method uses direct dilute acid extraction of the sample, followed by simultaneous measurement of the three elements using a three-channel atomic fluorescence spectrometer. The study demonstrates that the method is suitable for rapid screening and routine monitoring in grassroots inspection institutions.

Method Development and Optimization

The analytical method was developed with careful optimization of key parameters to achieve reliable simultaneous determination of the three elements. The following table summarizes the optimized method parameters:

The use of thiourea in the on-machine solution serves as a stabilizer for arsenic, preventing its decomposition during the measurement. Oxalic acid is used as a reducing agent to ensure the complete conversion of mercury to its volatile form for detection. The carrier solution concentration and the reducing agent composition were optimized to balance the sensitivity and stability of the signal for all three elements simultaneously.

Validation Results and Method Performance

The method was validated according to standard analytical chemistry protocols, with the following results:

The detection limits are well below the regulatory limits for these elements in edible salt, which are typically set at 10 micrograms/kg for lead, 1 microgram/kg for arsenic, and 0.05 micrograms/kg for mercury according to Chinese national food safety standards. The recovery rates, while slightly wider than ideal (80.8%-110%), are acceptable for screening and routine monitoring purposes. The RSD values indicate acceptable precision for a rapid simultaneous method.

Engineering Practice and Application in Quality Control

The development of this three-channel AFS method has significant practical implications for food safety monitoring, particularly in the context of grassroots inspection institutions that may lack access to more advanced analytical instruments such as inductively coupled plasma mass spectrometry (ICP-MS). The method offers several advantages for routine monitoring:

• Simultaneous measurement of three elements in a single analysis run, significantly reducing analysis time compared to sequential single-element measurements.
• Lower instrument cost and maintenance requirements compared to ICP-MS.
• Simple sample preparation using direct dilute acid extraction, minimizing the risk of contamination during sample handling.
• Suitable for high-throughput screening of salt samples in quality control laboratories.

The method is particularly valuable for monitoring the safety of edible salt, which is a basic food commodity consumed by large populations. Contamination of salt with heavy metals such as lead, arsenic, and mercury can occur through various routes, including raw material contamination, processing equipment leaching, and environmental pollution. Regular monitoring is essential to ensure compliance with food safety standards and to protect public health.

Key Questions and Reflections

This study raises an important question about the trade-off between analytical speed and accuracy in routine monitoring. The three-channel AFS method offers a significant speed advantage over sequential single-element analysis, but the wider recovery range and RSD values suggest that it may not be suitable for definitive measurements or legal enforcement actions. For such purposes, a more precise method such as ICP-MS would be required. The appropriate use of the AFS method would be for initial screening, with positive samples being confirmed by a more precise method.

Another reflection is the importance of method validation in analytical chemistry. The study demonstrates that the method was validated according to standard protocols, including linearity, detection limit, recovery, and precision assessments. The comparison with a standard method confirmed that the results were not significantly different, which is essential for establishing the method's validity. However, the study does not report on matrix effects, which can be significant in salt samples due to the high chloride concentration. Future work should investigate the matrix effects and their impact on the accuracy of the method.

Study Insights and Implications

This literature provides a practical analytical method for the rapid simultaneous determination of lead, total arsenic, and total mercury in edible salt. The fundamental lesson is that the development of rapid screening methods is essential for effective food safety monitoring, particularly in resource-limited settings. For engineers and analysts involved in food safety testing, this study reinforces the importance of:

• Developing methods that are suitable for the capabilities and resources of the target laboratory.
• Validating methods thoroughly before implementation to ensure reliable results.
• Understanding the limitations of rapid screening methods and using them appropriately in the analytical workflow.
• Ensuring that sample preparation procedures minimize contamination risks.

The paper is a valuable reference for analytical chemists and food safety inspectors who need to develop or implement methods for heavy metal monitoring in food commodities. It demonstrates that a well-optimized three-channel AFS method can provide a practical solution for routine monitoring, balancing speed, cost, and analytical performance.