A Chinese group of researchers has developed an analytical method for arsenic species that can be used for various seafoods such as seaweed, fish, shellfish and shrimp. Using microwave-assisted extraction, the extraction efficiency was better than 95% for all sample types without altering their original speciation.
Background:Arsenic, both from natural sources but also from industrial pollution, is reaching coastal seawater, contaminating marine organisms to relatively high concentrations due to bioaccumulation. Marine organisms can convert inorganic arsenic into various organic species after they intake or ingest inorganic arsenic from environment. Thus, marine organisms contain a variety of arsenic species of different toxicity, and different types of organisms contain different arsenic species. When using these organisms as seafood for human consumption, a meaningful risk assessment requires the information about the species distribution. Since different types of seafood not only contain different arsenic species but also have quite different matrix, many analytical methods have been developed for a specific sample type.
The new study:A group of Chinese researchers aimed at the development of a universal microwave-assisted extraction method to completely extract arsenic species in all fish, shellfish, seaweed and shrimp samples without altering original arsenic species. The separation and detection of the extracted arsenic species was based on a simple cation exchange IC-ICP-MS method, that did not require any further pretreatment.
The fresh biological sample materials were first freeze-dried and then ground to powder. A 100 mg aliquot of the sample material was weighed and placed into a 100 ml Teflon beaker, and 6.0 ml of 20 mmol/L HNO3 was added. The beaker was then placed at room temperature for 12 h to soak the samples. Subsequently, the beaker was placed into a microwave extraction apparatus to heat the sample to 120 °C within 10 min and hold the temperature for another 30 min. After the sample was cooled to room temperature, the extract was separated by centrifugation. The residue was extracted a second time by using 4 ml of 2o mmol/L HNO3 under the same microwave program. The two extracts were combined and the whole extract was diluted up to 5 times, depending on the total arsenic concentration, with pure water. The final solution was used for the IC-ICP-MS detection of arsenic species. The extraction time, temperature and acid concentration and leachate volume were optimized in order to achieve high sensitivity and highest extraction efficiency without changing the original speciation. The authors found that the pre-soaking step for 12 h was essential to achieve nearly quantitative extraction efficiency for fish and shellfish samples.
Each arsenic species including As(V), As(III), MMA, DMA, AsB, arsenosugars and unidentified As species were qualitatively analysed based on their retention time in IC separation and were quantitatively determined based on peak areas with external calibration. For the separation, seaweed samples are the more complex samples due to their complex speciation including arsenosugars. The separation of the different species was optimized by adding 5.0 mmol/L EDTA to the 5.0 mmol/L HNO3 solution as mobile phase. Using this mobile phase with a flow rate of 0.7 ml/min, arsenic species in seaweed (Sarcodia ceylanica) including As(V), As(III), arsenosugar (DMAsSugarMethoxy), DMA and AsB can be base-line separated and accurately detected by using IC-ICP-MS. The obtained detection limits were in the range of 0.10 ng/ml ± 0.02 ng/ml.
By analysing the different seafood samples, the authors demonstrated the broad applicability, high efficiency and excellent accuracy of their method.
The Original study
Yaohui Lin, Ying Sun, Xusheng Wang, Shilong Chen, Yongning Wu, FengFu Fu,
A universal method for the speciation analysis of arsenic in various seafood based on microwave-assisted extraction and ion chromatography-inductively coupled plasma mass spectrometry, Microchem. J., 159 (2020) 105592.
DOI: 10.1016/j.microc.2020.105592
Used techniques and instrumentation:
Agilent Technologies Inc. - 7800 ICP-MS
Thermo Scientific - Dionex ICS-900
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DOI: 10.1021/jf2040466
Brief Summary: LC-ICP-MS: The most often used hyphenated system for speciation analysis
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last time modified: September 19, 2024
