Runhua Li

Ultra-sensitive detection of heavy metal ions in tap water by laser-induced breakdown spectroscopy with the assistance of electrical-deposition

The trace heavy metal ions in tap water were electrically deposited on the surface of a high purity aluminium rod and then analyzed with laser-induced breakdown spectroscopy (LIBS). Cr3+, Mn2+, Cu2+, Zn2+, Cd2+ and Pb2+ in tap water samples were quantitatively analyzed and the calibration curves have been built up within the concentration range of 1–1000 μgL−1. The limits of detection of these ions were determined to be 0.16–1.35 μgL−1, which are improved 5–6 orders than directly analyzing aqueous solutions by LIBS. The influence of Ca2+ and Mg2+ in water at different concentrations to the quantitative analysis of trace heavy metal ions was evaluated. It is possible to realize reliable quantitative analysis by using different calibration curves according to the hardness of the analyzed water samples. LIBS plus electrochemical enrichment is a potential approach to high sensitivity detection of trace heavy metal ions in tap water and natural water samples, and it will find applications in environmental pollution monitoring.

Ultra-sensitive trace metal analysis of water by laser-induced breakdown spectroscopy after electrical-deposition of the analytes on an aluminium surface

Toxic heavy metals in water pose a potential health and environmental risk to people. The current techniques used for water trace metals analysis are either time-consuming or of low sensitivity. It is necessary to develop a fast and sensitive technique to monitor or analyze trace toxic heavy metals in water. In this work, the trace heavy metals of water were electrically deposited on the surface of a polished high purity aluminium plate and then quantitatively analyzed by laser-induced breakdown spectroscopy (LIBS). It was demonstrated that the electrical-deposition method significantly enhanced the sensitivity of detection by pre-concentration and elimination of water matrix interference. After 10 minutes deposition in 400 mL of water solution with 36 V deposition voltage, the limits of detections of Cr, Mn, Cu, Zn, Cd and Pb were determined to be 0.572, 0.374, 0.083, 5.623, 0.528 and 0.518 μg L−1, respectively. This approach provides a potential technique to perform direct ultra-sensitive analysis of toxic heavy metals in natural water samples, with the advantages of low cost, high sensitivity and the possibility of analyzing multi-elements simultaneously.

Laser ignition assisted spark-induced breakdown spectroscopy for the ultra-sensitive detection of trace mercury ions in aqueous solutions

The trace mercury ions in aqueous solutions were electrically deposited on the surface of a high purity copper plate and then quantitatively analyzed by laser ignition assisted spark-induced breakdown spectroscopy (LI-SIBS). Laser ignition is helpful to enhance discharge stability and reduce the required voltage level in SIBS. The analysis sensitivity of mercury in LI-SIBS was enhanced by a factor of 30 in comparison with that in laser-induced breakdown spectroscopy (LIBS). A 6% relative standard deviation has been achieved in multiple measurements and the limit of detection of mercury in aqueous solutions by LI-SIBS has reached to 2μgL−1 under present experimental conditions. LI-SIBS overcomes the low-sensitivity shortcoming of LIBS on the analysis of mercury. By combining with electrical deposition enrichment, LI-SIBS provides a simple and ultra-sensitive analysis method for mercury ions in water.

Ultrasensitive detection of trace amounts of lead in water by LIBS-LIF using a wood-slice substrate as a water absorber

To realize ultrasensitive detection of trace amounts of lead in water, laser-induced breakdown spectroscopy combined with laser-induced fluorescence (LIBS-LIF) was investigated. A wood-slice substrate was selected: (i) as a water absorber to convert liquid-sample analysis to solid-sample analysis; (ii) to eliminate the influence of a water matrix to spectral analysis (e.g., light blocking due to water splashing and plasma emission quenching due OH groups) in the plasma during direct analysis of water samples. The wood slice after treatment was ablated by a Q-switched Nd:YAG laser to produce plasma. Then, the lead atoms in the plasma were re-excited by a second tunable dye laser resonantly. The LIF signal of lead was detected to improve its sensitivity to spectral analysis significantly. Under the assistance of this matrix-converting method, the calibration curve of lead in water samples was created and the limit of detection was found to be 0.32 ppb, two orders of magnitude better than that obtained by analyzing water samples directly using the same LIBS-LIF technique. This sample-pretreatment procedure was rapid and easy to handle. Upon combination with LIBS-LIF, ultrasensitive detection of trace amounts of toxic metal elements in water could be realized. This approach could be applied in water-quality control and monitoring of environmental pollution.