Zinc by paper Chromatography

The above methods are concerned primarily with unused lubricants and consequently a report by Goodwin and Begeman^6 are of interest. This  article  describes a methods  of  tracing  Zinc dialkyldithiophosphate  decomposition  in axle lubricants by  paper  chromatography. For  the  purpose, a  sample  of the oil  was  allowed to  soak  into  a sheet  of filter paper after  which  the  paper  was suspended  in  a  chromatogram   above  a  developing  solvent. About 1/8 inch of the lower edge of the paper was immersed in the solution until the solvent front had traveled to within 1 ½ inches from the top.  Following this treatment, the paper was dried. Since  the  zinc  compounds  in the developed chromatograms  are  colorless, a colored  zinc  derivative  was formed  by spraying  the paper with a 0.05  per cent  solution of  diphenylthiocarbozone  (dithiozone)  in  chloroform. This formed a purplish red zinc dithioozonate. Any  excess  dithiozone  was  removed  by  immersing  in a weak  ammonium  hydroxide  solution and then  washing  with water. The  red  color  fades over  a period of days  but may be  photographed  with  color  films to give  a permanent record. The intensity of the color indicates the relative amount of zinc present. Thus, the intensity of colors in tests decreased considerably in the interval of road mileage from 2,006 to 5,144.