Isotope dilution gas chromatography/mass spectrometry for cadmium determination in urine.

A stable isotope dilution gas chromatographic/mass spectrometric method using 106Cd as an internal standard is described for determining Cd in urine. In this method, the urine matrix is digested with HNO3 + H2O2 and the Cd is chelated with lithium bis(trifluoroethyl)dithiocarbamate. All isotope ratio measurements are made with an organic mass spectrometer. Overall precision values for the five major isotopes relative to 114Cd are 1 to 3% when 10-ng samples of chelated Cd are analyzed. Accuracy of the method is established by measuring Cd in the NIST freeze-dried urine reference material. A small memory effect is observed when measuring isotope ratios differing by a factor of 10. This can, however, be minimized by optimum addition of the internal standard solution.