Spectrophotometric determination of chromium(III) and rhodium(III) after extraction with oxine into molten naphthalene

Conditions have been developed for the extraction of chromium(III) and rhodium(III) as their 8-hydroxyquinolinates into molten naphthalene. The naphthalene is allowed to solidify, separated by filtration, dried with filter paper and dissolved in chloroform. The solution is diluted to 10 ml and its absorbance measured at 410 nm for chromium and 425 nm for rhodium, against a reagent blank. In both cases the solution is stable for 24-36 hr. Beer's law is obeyed over the range of 2.7-48.6 mug of chromium or 2.7-57.5 mug of rhodium in 10 ml of the chloroform solution. The molar absorptivity is 3 x 10(3) l. mole(-1) . cm(-1) for chromium and 3.6 x 10(4) for rhodium. Solutions containing 27.0 mug of chromium or 10.95 mug of rhodium give a mean absorbance of 0.140 and 0.395 respectively, with standard deviations of 0.002(2) and 0.004(7). Most metal ions that form oxinates may interfere, but can be removed beforehand by normal liquid-liquid extraction.