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

Abstract

A flow injection (FI) on-line precipitation–dissolution was developed for electrothermal atomic absorption spectrometry (ETAAS) determination of (ultra)trace amounts of beryllium in water samples. Beryllium was precipitated quantitatively with NH 4OH+NH 4Cl and collected in a knotted tube of Tygon without using a filter, while the other matrix components flowed downstream to waste. The precipitate was dissolved with nitric acid and a sub-sample was collected in a capillary of a sampling arm assembly, to introduce 10 μl 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 μg of Lu (in 20 μl) by the spectrometer autosampler. The effect of a number of possible cations on the beryllium precipitation process was studied. While, the addition of Ba 2+, Sr 2+, Ca 2+, Mg 2+, Mn 2+, Zn 2+, Co 2+ and Ni 2+ did not produce any perceptible precipitate on the reaction coil walls, the addition of Al 3+, Cr 3+ and Fe 3+ produced large precipitated particles. However, their tolerance limit was well above the levels at which theses species are commonly found in most natural waters. The detection limit (3σ) 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 enrichment 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, avoiding time-consuming manual work and enhancing the reproducibility and precision of the determination of beryllium. The results obtained for the determination 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.