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

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