Spectrophotometric determination of aliphatic thiols by using redox color reaction of copper-1,10-phenanthroline

Tamio KAMIDATE, Atsushi KATAYAMA, Hiroto WATANABE
1988 Analytical Sciences  
Volatile aliphatic thiols are typical air pollutants. The aliphatic thiols are usually measured by gas chromatography and electrochemical detection after dissolution of samples into organic solvent.'-3 However, a spectrophotometric method for the aliphatic thiols is not established though many spectrophotometric methods have been widely used for water-soluble thiols such as glutathione.a-5 Copper(II) ion reacts with thiols to form copper thiolato complex and disulfide in aqueous solvents. In
more » ... ous solvents. In the course of our studies on the oxidation of the aliphatic thiols with metal complex ions in various solvents, we have found that Cu(II)-1,10-phenanthroline (phen) complex ion in dimethyl sulfoxide (DMSO) is quantitatively reduced by aliphatic thiols to the intensely colored copper(I)-phen complex ion without any formation of copper thiolato complex. Based on this finding we propose a method for the spectrophotometric determination of the aliphatic thiols. Experimental [Cu"(phen)n]2+ complex ion solutions were prepared by dissolving copper(II) nitrate (final concentration; 1.OX 10-2 mol dm-3) and phen (4.0X102 mol dm-3) in DMSO or a mixture of DMSO and distilled deionized water (water). Standard solutions of 1-propanethiol, 1-butanethiol, 1-hexanethiol and 1-octanethiol were made by dissolving 0.10 cm3 of the thiols in hexane, respectively, and diluting to 25 cm3. A working solution (from 5X10-6 to 1.5X10-4 mol dm-3) was prepared by the subsequent dilution of the standard solutions with hexane. All reagents used were of a reagent grade and were used without further purification. Disulfide and unreacted aliphatic thiols in hexane were measured with a Hitachi 663-30-type gas chromatograph. Absorption spectra of copper complex ion were measured with a Hitachi 124 type spectrophotometer equipped with 1-cm quartz cells. The redox reaction between the aliphatic thiols and [Cu"(phen)n]2+ ion was made according to the recommended procedure shown below: Equal volumes (10 cm3) of the [Cu"(phen)n]2+ ion solution and hexane containing thiol are placed together in a 50-cm3 separatory funnel, and the mixture is shaken for 15 min at room temperature. After phase separation, the absorption spectra of [Cu'(phen)n]+ ion in the DMSO phase are measured against the reagent blank. Results and Discussion Oxidation of 1-butanethiol (2.0X10-2 mol dm-3) with [Cu"(phen)n]2+ ion (1.0X10-2 mol dm-3) was examined to establish the stoichiometry of the redox reaction between 1-butanethiol and [Cu"(phen)n]2+ ion in aqueous-DMSO solutions. The result of analysis of the reaction products is shown in Fig. 1 . When the DMSO volume percent was greater than 95%, equimolar amounts of 1-butanethiol (RSH) and [Cu"(phen)n]2+ ion reacted to form disulfide (RSSR) according to the following equation: 2[Cu" (phen)n]2++2RSH 2[C&(phen)n]++RSSR+2H+
doi:10.2116/analsci.4.329 fatcat:q4aenol5xbhsraf54hc3fpveyq