A new spectrophotometric titration method is proposed for determination of the amounts of metal chelates present in nonaqueous solvents. The titrant is a standard solution of a chelating agent which quantitatively displaces the chelate anion of the metal chelate. The method is exemplified by the titration of pg amounts of the dithizonates of Ag, Pb, Cu(II), Cd, Zn, and In in chloroform, both in the absence and the presence of free dithizone. Some binary and ternary mixtures were also successfully analyzed for the individual metal dithizonates. The titrant was a standard solution of sodium diethyldithiocarbamate in ethanol. Precision and accuracy were good. The preparation and analysis of the metal dithizonates are described. New titrimetric procedures are also proposed and shown to be satisfactory for determination of the free dithizone content of a chloroform solution.Canadian Journal of Chemistry, 47, 4543 (1969) IntroductionThe present work demonstrates that a chelating agent in a nonaqueous solvent can be a useful titrant for metal chelates present in low dielectricconstant solvents. The overall reaction is the quantitative replacement of the chelate anion of the undissociated metal chelate by the titrant. The term chelate-exchange titration seems appropriate. The example studied is the spectrophotometric titration of pg amounts of the dithizonates of Ag, Pb, Cu(II), Cd, Zn, and In in chloroform; the titrant was sodium diethyldithiocarbamate in ethanol. The initial presence of free dithizone in the chloroform solution was found not to affect the accuracy of the results.RGiiEka and Starjr (1) were the first to suggest the possibility of using chelate-exchange titrations, in particular for the determination of the metal content of the organic solvent phase from a solvent extraction procedure. Extraction of metals as neutral. undissociated chelates into low

A new method is proposed for the determination of milligram amounts of each halide present in a mixture of alkali-metal halides. I n some mixtures, thiocyanate also may be determined. A methanol solution of the sample is titrated in a closed-type cell, with a standard solution of silver nitrate in methanol. By using high-frequency titrimetry, and an appropriate concentration of the halide solution, sharp end points were obtained for each halide. Because of solid solutions, the accuracy of the determination of individual halides in mixtures depended on the mole ratios of the halides; the errors found in the titration of various binary, ternary, and quaternary mixtures are reported. For some binary mixtures, the total amount of halide titrated in 120 ml of methanol was varied from 0.5 t o 500 micromoles. A t the lower concentrations, addition of a small amount of sodium nitrate sharpened the end point. A t all conce~ltrations of halide, an excessive amount of indifferent electrolyte essentially eliminated the end points. The alkali-metal halides gave more satisfactory titration graphs than did some other metal halides. The effects of variation in temperature, and of solvent evaporation were noted.

A n automated method has been developed t o determine arsenic and lead i n pre-treater, reforming and other catalysts using microwave digestion and atomic absorption spectrometry with electrothermal atomisation. The proposed method is precise and accurate with a practical lower limit of determination i n the catalyst of 10 m g kg-1 for arsenic and 5 m g kg-1 for lead.

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Chelate-exchange titrimetry has been applied to the determination of μg amounts of some metal 8-quinolinates in benzene. The titrant was a standard solution of diphenylthiocarbazone in benzene. Accuracy and precision were good in the cases of Pb, Cu(II), Cd, Zn, and In. Very slow reaction rates made titrations of Ag and Ni impracticable, and chelate-exchange was negligible in the case of Co(II). A new titrimetric method is also shown to be precise and accurate for the determination of free 8-quinolinol in benzene; the titrant was a standard solution of Cu(NO3)2 in ethanol.