Sensitive cesium measurement in liquid sample using low-pressure laser-induced breakdown spectroscopy

•The sensitive cesium measurement method of liquid phase in liquid jet was developed using LIBS.•The distinct and round profile of plasma can be acquired under reduced pressure condition compared with that at atmosphere pressure.•The difference between plasma emission and Cs emission was discussed under various experimental conditions.•The detection enhancement process was elucidated by analyzing the effects of laser focal point and plasma measurement area.•The Cs detection limit of 22.8 ppb (1 minute) was achieved at 26 kPa in current experimental conditions.

The environmental pollution by trace heavy metals is a severe problem for the environment and human health. In this paper, the liquid jet of CsNO3 solution employed was introduced to the measurement chamber and detected using laser-induced breakdown spectroscopy (LIBS) directly at low pressure to determine the detection features of trace Cs element in liquid. The distinct and round plasma can be acquired when reducing the pressure. The interaction between the plasma core of the liquid jet and the surrounding gas can be controlled to enhance Cs detection ability. Cs emission was mainly in the surrounding area in the plasma. The influences of laser focal point and plasma measurement area on the measured signals were studied under low-pressure condition. When employing the defocus mode and varying the measurement area within a certain range, Cs signal and the signal-to-background ratio were improved. Cs detection limit can reach to 22.8 ppb (3σ/ms) at pressure of 26 kPa in this paper. According to the discussion, the detection limit will be enhanced when improving the experimental conditions using this method, which shows the great application potential of liquid sample measurement.