Measurement of the rubidium content in a standard reference sample applying isotope dilution in diode laser graphite furnace atomic absorption spectrometry

The reliability of the isotope dilution technique applied to diode laser gr aphite furnace atomic absorption spectrometry was tested by the determinati on of the Rb content in a NIST (National Institute of Standards and Technol ogy) reference water (SRM 1640). For the measurements, the NIST water was s piked with different amounts of Rb-87. The signals of both naturally occurr ing Rb isotopes, Rb-85 and Rb-87, were measured simultaneously by the use o f 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).