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The spectrophotometric determination of trace amounts of phenols was investigated for flowinjection analysis. Phenols reacted with 4-aminoantipyrine(4-AAP) to form stable antipyrine dyes, which were concentrated on a Teflon(PTFE) filter tube. The antipyrine dyes collected on the filter tube were eluted with 99% ethanol. The conditions for the antipyrine dye synthesis used in this study were remarkably different from that for the conventional batch method. Because a large excess of 4-AAP interferes with the adsorption of antipyrine dyes on a Teflon filter tube, 4-AAP was used at a lower concentration than that of the batch method. As a result, the reaction of antipyrin dye synthesis consumed a long time. Concerning the pH for the synthesis of antipyrine dyes, 7.3 was selected from the standpoint of the collection efficiency for the antipyrine dyes. The sensitivity of the determination of phenols by the present method was enhanced by 18 times compared to other concentration methods using Amberlite XAD resin. The detection limits was 0.04 μg l for phenols for a concentration time of 15 min. The optimum procedure for the determination of phenols by the present method was as follows : a sample solution containing less than 5 μg of phenols was adjusted with a KH2PO4-K2HPO4 buffer solution to pH 7.3. Then, 0.5 ml of 0.04% 4-AAP and 1.0 ml of 0.16%KFe(CN)6 were added to the solution. The sample solution was left standing for 15 min to produce antipyrine dye. The obtained dye solution(100 ml) was transported to a Teflon filter tube at a flow rate of 1.6 ml/min for 15 min. The absorbance of the dyes eluted with ethanol (1.6 ml/min) was measured at 510 nm. The phenols were determined over the range of 0.5~40 μg l. The RSD was 2.1% for 0.5 μg l phenols (n=7). Aniline and its derivative interfered with the determination of phenols at more than 10 times the amount of phenols. Inorganic ions did not interfere with the determination of phenols except for sodium sulfite.

On-line concentration method using Teflon filter tube for spectrophotometric determination of trace amounts of phenols.