Abstract

The reliability of the isotope dilution technique applied to diode laser graphite furnace atomic absorption spectrometry was tested by the determination of the Rb content in a NIST (National Institute of Standards and Technology) reference water (SRM 1640). For the measurements, the NIST water was spiked with different amounts of ⁸⁷Rb. The signals of both naturally occurring Rb isotopes, ⁸⁵Rb and ⁸⁷Rb, were measured simultaneously by the use of two diode lasers. A total Rb content of 1.97 ± 0.03 ng ml⁻¹ was found which compares very well with the reference value of 2.00 ± 0.02 ng ml⁻¹.