Photoacoustic Determination of Cobalt after Solid-Phase Concentration on an Empore Silica-gel Thin-Layer Plate

Abstract

A method used to determine trace amounts of samples in aqueous solutions is proposed. Cobalt ion was extracted as a l-(2-pyridylazo)-2-naphthol (PAN) complex into chloroform. The extract was filtered through an Empore silica-gel TLC plate (2.5 cm square) having no backing material. Excessive PAN and other metal-PAN complexes were washed out through the TLC plate by filtering twice 5 ml of chloroform. Using these procedures only the cobalt-PAN complex was concentrated on the surface of the TLC plate. The photoacoustic signal of the TLC plate was detected by using a He-Ne laser as a light source. A linear relationship was obtained between the concentration of cobalt and the photoacoustic intensities in the 0.1–20 ppb range. A five-hundred-times concentration of Ni, Cu and Fe did not significantly interfere with the photoacoustic signal. The determination limit of cobalt when the sample volume was 100 ml was about 0.15 ppb.