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We have found a little suppression of superconductivity at xϭ0.21 in La 2Ϫx Sr x CuO 4 single crystals and, moreover, a giant suppression of superconductivity at xϭ0.21 through the 1% substitution of Zn for Cu. In the Zn-substituted La 2Ϫx Sr x Cu 1Ϫy Zn y O 4 single crystal with xϭ0.21 and yϭ0.01, the resistivity exhibits an upturn at low temperatures below ϳ80 K. These results suggest that the dynamical stripe correlations of spins and holes are pinned by a small amount of Zn at xϭ0.21, leading to a static stripe order and the giant suppression of superconductivity, as in the case of xϭ0.115.

A simple and convenient x-ray fluorescence analysis procedure for trace amounts of Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb in water was developed using preconcentration with an iminodiacetate extraction disk (IED). The IED was coated on both faces with commercially available laminate film to prevent x-ray damage to the IED by strong x-irradiation (4 kW; 50 kV, 80 mA) of the wavelength-dispersive x-ray fluorescence spectrometer. Lamination of the IED prolongs its life from 7 to about 200 min at 4 kW irradiation while negligibly decreasing the x-ray fluorescence. Lowering the power of primary x-rays to less than 1.5 kW compensated for the Hg evaporation. Linear calibration curves were obtained over the range 500 µg-5 mg for Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb. Detection limits corresponding to three times the standard deviation of the blank intensity were 0.1-0.4 µg for Mn, Co and Ni, 0.5-0.8 µg for Fe, Cu, Zn and Pb and 7 µg for Cd. A spike test for 10 µg of eight analytes, excluding Mn, showed good recoveries (90-100%) for city water and rainwater. Analytical results for municipal tap water and rainwater agreed well with values obtained using atomic absorption spectrometry.