Determination of beryllium in natural and waste waters using on-line flow-injection preconcentration by precipitation/dissolution for electrothermal atomic absorption spectrometry

A flow injection (FI) on-line precipitation-dissolution was developed for e lectrothermal atomic absorption spectrometry (ETAAS) determination of (ultr a)trace amounts of beryllium in water samples. Beryllium was precipitated q uantitatively with NH4OH + NH4Cl and collected in a knotted tube of Tygon w ithout using a filter, while the other matrix components flowed downstream to waste. The precipitate was dissolved with nitric acid and a sub-sample w as collected in a capillary of a sampling arm assembly, to introduce 10 mu l volumes into the graphite tube by means of positive displacement with air through a time-based injector. This sequence was timed to synchronize with the previous introduction of 6 mu g of Lu (in 20 mu l) by the spectrometer autosampler. The effect of a number of possible cations on the beryllium p recipitation process was studied. While, the addition of Ba2+, Sr2+, Ca2+, Mg2+, Mn2+, Zn2+, Co2+ and Ni2+ did not produce any perceptible precipitate on the reaction coil walls, the addition of Al3+, Cr3+ and Fe3+ produced l arge precipitated particles. However, their tolerance limit was well above the levels at which theses species are commonly found in most natural water s. The detection limit (3 sigma) of 25 ng l(-1) in the sample solution, was obtained. The precision of the method, evaluated by ten replicate analyses of solutions containing 20 and 200 pg of beryllium were 4.8 and 4.0% (n = 5), respectively. Enrichment factors from 7.0 to 10.3 and from 10.5 to 13.8 were obtained for precipitation times from 25 to 38 s and from 43 to 50 s for waste and tap waters, respectively. These results indicate that the enr ichment factor was limited by the interference of some matrix metals which could precipitate as hydroxides (or related species) and be retained in the reaction coil. The integrated system permits fully automated operation, av oiding time-consuming manual work and enhancing the reproducibility and pre cision of the determination of beryllium. The results obtained for the dete rmination of beryllium in certified reference materials (trace elements in water), together with the good recovery of spiked analytes, demonstrate the applicability of the procedure to the analysis of natural waters. (C) 2000 Elsevier Science B.V. All rights reserved.