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Laser-induced breakdown spectroscopy (LIBS) shows promising applications in the analysis of environmental heavy metals. However, direct analysis in water by LIBS faces the problems of droplet splashing and laser energy decay. In this study, a novel liquid–solid conversion method based on agarose films is proposed to provide an easy-to-operate and sensitive detection of heavy metals. First, the water samples were converted into semi-solid hydrogels with the aid of agarose and then dried into agarose films to make the signal intensities stronger. The calibration curves of Cd, Pb and Cr were constructed. The proposed method was validated by standard heavy metal solutions and real water samples. The results showed that the values of R2 were 0.990, 0.989 and 0.975, and the values of the LOD were 0.011, 0.122 and 0.118 mg L−1 for Cd (I) 228.80, Pb (I) 405.78 and Cr (I) 427.48 nm, respectively. The RMSEs of validation were 0.068 (Cd), 0.107 (Pb) and 0.112 mg·L−1 (Cr), and the recovery values were in the range of 91.2–107.9%. The agarose film-based liquid–solid conversion method achieved the desired ease of operation and sensitivity of LIBS in heavy-metal detection, thereby, showing good application prospects in heavy metal monitoring of water.

In order to rationally apply potassium fertilizer, it is very important to realize the rapid and accurate evaluation of soil available potassium (K). Conventional methods are time-consuming, consumables-consuming and laborious. A high-efficiency method was proposed in this study to meet the demand for rapid evaluation, including rapid extraction, uniform evaporation and LIBS detection. To shorten the extraction time, we increased the oscillation frequency and removed the operation of dry filtration. Compared with the conventional extraction method of the Chinese national standard (CNS), the extraction time was reduced from 30 min to 2 min. In addition, we developed a uniform evaporation method for liquid–solid transformation on the batch-detection fixed area aluminum substrate. This method reduced the moisture interference. At the same time, increasing the liquid viscosity and restricting the liquid area and shape could reduce the coffee ring effect (CRE). The determination coefficient of the calibration curve by our method was 0.99, and the limit of quantitation reached 0.8 mg/kg. Real soil samples were taken as validation, and the average relative error between our method and the CNS method was 3.58%. The results indicate that our method combined with LIBS technology could provide a fast and accurate evaluation of soil available K.