Fig. 1. Diagram of LIBS experimental setup

Fig. 2. LIBS sample preparation process for detection of soil heavy metals

Fig. 3. Spectral line selection. (a) Comparison of spectra before and after enrichment of chelating resins; (b) comparison of spectral intensity between resin enrichment method and soil tableting method

Fig. 4. Effects of enrichment time on intensity values of Cu characteristic lines

Fig. 5. Effects of resin dosage on intensity values of Cu characteristic spectral lines

Fig. 6. Effects of pH value on intensity values of Cu characteristic lines

Fig. 7. Effects of laser energy on intensity values of Cu characteristic lines. (a) Cu I 324.75 nm; (b) Cu I 327.39 nm

Fig. 8. Effects of ICCD delay time on intensity values of Cu characteristic lines. (a) Cu I 324.75 nm; (b) Cu I 327.39 nm

Fig. 9. Space constraint device. (a) Enhancement effect of plasma; (b) V-shaped space constraint device

Fig. 10. Effects of spatial constraint on intensity values of Cu characteristic lines. (a) Cu I 324.75 nm; (b) Cu I 327.39 nm

Fig. 11. Comparison of calibration curves before and after adding spatial constraint. (a) Cu I 324.75 nm;(b) Cu I 327.39 nm