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-mod ulation laser diode absorption spectrometry in graphite furnaces) tech nique for detection of Rb at low pg ml(-1) concentrations in samples w ith complex matrices has been performed. Five reference materials were investigated with respect to their Rb content by the WM-LDAS-GF techn ique: corn bran (NIST 8433); NIST water; (1643d) riverine water (SLRS- 2); estuarine water (SLEW-1); and sea water (NASS-3). Freeze-dried cor n bran was found to have a Rb concentration of 440 +/- 70 ng g(-1). Th is 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 m l(-1). This compares excellently with the specified (although not cert ified) level of 13 ng ml(-1). None of the three other reference materi als has any certified Rb level. The Rb content of riverine water was f ound to be 3.4 +/- 0.8 ng ml(-1). Chemical interferences were encounte red when estuarine water and sea water were analyzed (loss of Rb as Rb Cl). Addition of NH4NO3 as the matrix modifier increased the Rb recove ry values considerably (although not fully to unity). Estuarine water and sea water were found to have Rb contents of 30 +/- 10 ng ml(-1) an d 140 +/- 50 ng ml(-1), respectively. A detection limit for Rb in deio nized 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. T hese results show that the WM-LDAS-GF technique is capable of detectin g traces of Rb in samples also with complex matrices. (C) 1997 Elsevie r Science B.V.