Ion-pair extraction of silver ion into chloroform has been studied with benzo-monothia-15-crown-5 (5,6-benzo-1,4,7,10-tetraoxa-13-thiacyclopentadeca-5-ene, B-15TC) in the presence of a counter anion. B-15TC was synthesized from catechol via 1,2-bis(2'-hydroxyethoxy)-benzene and 1,2-bis(p-toluenesulfonyl- oxyethoxy)-benzene in three steps. Counter anions studied were perchlorate and picrate ions, bromothymol blue (BTB), bromocresol green (BCG), ethyl orange (EO), cobalt(III)-dihydroxyazobenzene complex (Co-DHAB). The order of percent extraction was BTB > Co-DHAB > BCG > picrate ion > EO > perchlorate ion at pH less than 4 and BTB > Co-DHAB > BCG > EO > picrate ion > perchlorate ion at pH larger than 4. Silver ion was quantitatively extracted into chloroform at pH of 4.5-5.2 in the presence of BTB. The compositions of the extracted species are Ag~+ : B-15TC : BTB~- = 1:1:1 and 1:2:1. With the combined use of the extraction concentration and one-drop flame atomic absorption spectrometry using 50 μl volume of the chloroform extract, silver in a standard botanical sample of National Institute of Environmental Studies, NIES-CRM No. 9 Sargasso, was determined.
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