On-site analysis of iodine and its speciation in seawater is important for the prediction of radioactive iodine contamination. However, current methods, both colorimetric and instrumental, cannot meet the recent demand for field analysis and an increased reliability of results. Herein, a solid-phase fluorescence filter effect (SPFFE) induced by iodine was found and further used to develop a ratiometric fluorescence paper analysis device (RFPAD) for the analysis of iodine and its speciation in seawater. The proposed SPFFE-based assay surpasses the sensitivity and interference limitations arising from a specific extinction coefficient and multiple absorbers during real sample analysis, yielding an ultralow limit of detection of 550 pM for iodine. In conjunction with a smartphone, a developed program, and a sensing platform, both field-sensitive detection and speciation analysis of iodine could be achieved. An RFPAD was successfully used for the field speciation analysis of iodine and iodate in the South China Sea, showing excellent anti-interference capability and retaining promising potential for warning about radioactive iodine contamination in the ocean.

The application of headspace solid-phase microextraction (HS-SPME) for mercury preservation and detection still has several shortcomings, including the use of high-temperature desorption chamber, the consumption of expensive reagent (NaBEt 4 or NaBPr 4 ), and analyte loss during sample storage. Herein, a self-heating HS-SPME device using a gold-coated tungsten (Au@W) fiber was developed for the field detection of mercury in soil by miniature point discharge optical emission spectrometry (μPD-OES). Hg 2+ was reduced to Hg 0 with NaBH 4 solution and then preconcentrated with the Au@W fiber. The adsorbed Hg 0 could be rapidly desorbed by directly heating the fiber with a mini lithium battery and subsequently detected by μPD-OES. A limit of detection (LOD) of 0.008 mg kg −1 was obtained with a relative standard deviation (RSD) of 2.4%. The accuracy of the self-heating HS-SPME was evaluated by analyzing a soil certified reference material (CRM) and nine soil samples with satisfactory recoveries (86−111%). Compared to the conventional external heating method, the proposed method reduces desorption time and power consumption from 80 s and 60 W to 20 s and 2.5 W, respectively. Moreover, the self-heating device enables the μPD-OES system to remove the high-temperature desorption chamber, making it more compact and suitable for field analytical chemistry. Interestingly, the Au@W SPME fiber can be also used for the long-term preservation of mercury with a sample loss rate <5% after 30 days of storage at room temperature.

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