Determination of Cadmium in Very Low Concentration Urine Samples by Electrothermal Atomic Absorption Spectrometry

Abstract

Urine samples were collected that contained concentrations of Cd between 0.05 and 0.5 µ g l ^-1 . When using ETAAS for the analysis of these samples, spectral interference is present that can obscure low masses of Cd and deteriorate the precision and accuracy of the analysis. Instrumental advances such as electrodeless discharge lamps, the use of echelle monochromators, solid-state detectors and end-capped spatially isothermal atomizers have been combined to reduce detection limits. Spatially isothermal atomizers provided with end-caps and modified contact cones were found to double the sensitivity for Cd, compared with a standard atomizer configuration. A combined chemical modifier of Pd and NH ₄ NO ₃ can reduce interference from molecular alkali halides, on atomization of Cd. Samples were decomposed with boiling HNO ₃ to destroy carbon compounds and ensure homogeneity. Calibration was by standard additions to ensure accuracy in the determination; however, standard calibration may be used with a deterioration in accuracy of about 6%. For a sample containing 0.1 µ g l ^-1 Cd, the method including sample pre-treatment gives a precision of about 15%. The accuracy of the method was established by standard additions to samples and the analysis of a urine reference material; the instrumental detection limit is 0.008 µ g l ^-1 Cd in urine.