Fast and effective detection of lead (Pb) and cadmium (Cd) metals in water is the goal of M. Sadegh Cheri and S.H. Tavassoli of Shahid Beheshti University (Tehran, Iran); they have created a laser-induced-breakdown spectroscopy (LIBS) system relying on a laminar water jet to eliminate problems of splashing. Because the water position is well known, only small amounts of liquid are vaporized and the repeatability is improved. As a result, the researchers found that the limit of detection (LOD) for Pb was three times better than for other studies.
A Q-switched Nd:YAG laser emitting pulses of 150 mJ energy, 6 ns duration, and 5 Hz repetition rate created the required plasma when focused on a 5-cm-long downward vertical laminar water jet generated from a 1-mm-diameter nozzle. Light emitted by the plasma is channeled by an optical fiber to an echelle spectrometer with an intensified CCD and a fast photodiode to generate a trigger signal. With delay times of 1 to 5 μs, output from 50 pulses are accumulated to produce one spectrum and three such spectra measured. To eliminate experimental fluctuations, the spectra of Pb and Cd were normalized to that of hydrogen (Hß). The LODs measured for Pb and Cd were 4 and 68 parts per million, respectively. Contact S. H. Tavassoli at [email protected].