Measurements of rubidium in standard reference samples by wavelength-modulation diode laser absorption spectrometry in a graphite furnace

An investigation of the capabilities of the WM-LDAS-GF (wavelength-modulation laser diode absorption spectrometry in graphite furnaces) technique for detection of Rb at low pg ml(-1) concentrations in samples with complex matrices has been performed. Five reference materials were investigated with respect to their Rb content by the WM-LDAS-GF technique: corn bran (NIST 8433); NIST water; (1643d) riverine water (SLRS-2); estuarine water (SLEW-1); and sea water (NASS-3). Freeze-dried corn bran was found to have a Rb concentration of 440 +/- 70 ng g(-1). This compares well with the certified concentration of 500 +/- 300 ng g(-1). The Rb content of the MST water was assessed to 12.7 +/- 1.7 ng ml(-1). This compares excellently with the specified (although not certified) level of 13 ng ml(-1). None of the three other reference materials has any certified Rb level. The Rb content of riverine water was found to be 3.4 +/- 0.8 ng ml(-1). Chemical interferences were encountered when estuarine water and sea water were analyzed (loss of Rb as RbCl). Addition of NH4NO3 as the matrix modifier increased the Rb recovery values considerably (although not fully to unity). Estuarine water and sea water were found to have Rb contents of 30 +/- 10 ng ml(-1) and 140 +/- 50 ng ml(-1), respectively. A detection limit for Rb in deionized water of 10 fg (corresponding to a concentration of 1 pg ml(-1) using a 10 mu L aliquot) was obtained. This is identical to (and thus verifies) the previously published result by the group of K. Niemax. These results show that the WM-LDAS-GF technique is capable of detecting traces of Rb in samples also with complex matrices. (C) 1997 Elsevier Science B.V.