Spectrophotometric Determination of Polyoxyethylene Nonionic Surfactants in Ground Waters Using Triple-Stage Solid-Phase Extraction Followed by an Improved Ferric Thiocyanate Complexation Method. - Yokoyama, Yukio; Okabe, Toshiaki; Kubo, Hidetaka; Sato, Hisakuni (Microchimica Acta, 2005)