Volume 55, Number 9, 2001 APPLIED SPECTROSCOPY 1229 0003-7028 / 01 / 5509-1229$2.00 / 0 q 2001 Society for Applied Spectroscopy Spectrochemical Analysis of Metal Elements Electrodeposited from Water Samples by Laser-Induced Shock Wave Plasma Spectroscopy MARINCAN PARDEDE, HENDRIK KURNIAWAN,* MAY ON TJIA, KAZUHIRO IKEZAWA, TADASHI MARUYAMA, and KIICHIRO KAGAWA Applied Spectroscopy Laboratory, Graduate Program in Opto-Electrotechniques and Laser Application, Faculty of Engineering, The University of Indonesia, 4 Salemba Raya, Jakarta 10430, Indonesia (M.P., H.K.); Department of Physics, Faculty of Mathematics and Natural Sciences, Bandung Institute of Technology, 10 Ganesha, Bandung, Indonesia (M.O.T.); The Wakasa Wan Energy Research Center, 64-52-1, Nagatani, Tsuruga, Fukui 914-0192, Japan (K.I., T.M.); and Department of Physics, Faculty of Education and Regional Studies, Fukui University, 9-1 bunkyo 3-chome, Fukui 910, Japan (K.K.) We have succeeded in applying laser-induced shockwave plasma spectroscopy (LISPS) to the problem of the detection and analysis of metal elements deposited from water samples by means of elec- trolysis. It is shown that metal elements are generally deposited in the form of a thin lm on the electrode surface, while the electrode also conveniently serves as a subtarget for the relatively soft metal lm, thereby providing the necessary conditions for the generation of shockwave plasma, which is favorable for highly sensitive spec- trochemical analysis. It is shown that the detection sensitivity of this method reaches its highest value at low surrounding air pressure of around 1 torr. The lowest detection limit attained for various metal elements investigated in this experiment varies from around ten to a few tens of ppb. This limit can be readily improved upon by incorporating an optical multichannel analyzer into the detection system. We have thus presented a promising method for the reali- zation of a compact mobile monitoring system for the accurate con- trol of water and soil quality. Index Headings: Spectrochemical analysis; Electro-deposition tech- niques; Water analysis; Soil analysis; Laser-induced shockwave plasma spectroscopy. INTRODUCTION Recently there has been a rising demand for a low cost, portable, and highly sensitive method for the analysis of water and soil and applicable to rapid eld inspection of environmental pollution. In order to detect important and harmful elements such as heavy and poisonous metals in water, extremely high detection sensitivity is required as those elements are often hazardous in even trace amounts. In an effort to improve sensitivity, some researchers have proposed a new technique by combining electrothermal atomic absorption spectrometry (ETAAS) with the elec- trodeposition method, which is used to collect elements in water in the form of a thin layer on an electrode. 1–5 However, this technique is limited by its inadequacy for multi-element analysis. There is reason to expect that this shortcoming will be overcome by combining the electro- deposition method with the technique of atomic emission spectroscopy. In particular, the laser ablation emission spectrochemical analysis (LAESA) method offers the most promising alternative for this purpose because laser ablation is quite suitable for exciting the atoms in a thin lm layer. Received 14 November 2000; accepted 10 May 2001. * Author to whom correspondence should be sent. There are two main lines of development of LAESA. The rst one adopts a high-pressure surrounding gas and is commonly known as laser-induced breakdown spec- troscopy (LIBS). 6–10 In this method, a high power laser with short duration, such as a pulsed Nd:YAG laser, is focused onto a solid, liquid, or gas sample under atmo- spheric pressure. For liquid analysis, the laser is focused directly on the water droplet 7,11–13 or on the water painted on some solid surface. 14,15 This water analysis technique has been applied to environmental inspection and process control, such as the determination of uranium in solution for nuclear fuel reprocessing. 7 However, there are several limitations to the LIBS technique. One of the major lim- itations is its poor detection limit due to the strong con- tinuous emission background, which is inherent to plasma produced at high pressures. Another important limitation is associated with the lack of linearity between the emis- sion intensity of the analytical line and the concentration of the corresponding element in the sample due to the occurrence of self-absorption. Another line of development in LAESA is undertaken with the use of low surrounding gas pressure. 16–26 We have shown in a series of experiments 27–41 that plasma charac- teristics favorable to spectrochemical analysis are pro- duced when a pulsed laser such as a N 2 laser, 27 excimer laser, 28,29 TEA CO 2 laser, 30–41 or Nd:YAG laser 42,43 is fo- cused onto a solid target at reduced pressure of around 1– 10 torr. The laser plasma induced in this case generally consists of two distinct parts. The rst part is a small, high temperature plasma (primary plasma), which gives off an intense continuous emission spectrum for a short time just above the surface of the target. The second part (the sec- ondary plasma) expands with time around the primary plasma, emitting sharp atomic spectral lines with negligi- bly low background signals. On the basis of time-resolved experiments using a TEA CO 2 laser and an excimer la- ser, 28–33 we demonstrated that atoms in the secondary plas- ma were excited by the shockwave, while the primary plasma acted as an initial explosion energy source. We have referred to this method as laser-induced shockwave plasma spectroscopy (LISPS). It was also shown in pre- vious works that the hardness of the sample was a crucial condition for plasma generation in LISPS. In other words, LISPS cannot be applied directly to liquid or soft solid samples. We have nevertheless proven that even for a soft