Ultrasonic extraction as a sample preparation technique for elemental analysis by atomic spectrometry

This work presents performance data after ultrasonic extraction (UE) for th e elemental analysis of a number of metal species in samples of interest in environmental and occupational health. In this study, several National Ins titute of Standards and Technology (NIST) Standard Reference Materials(R) ( SRMs) were subjected to UE in various acid solutions. The extraction soluti ons employed were 25% nitric acid (v/v), 25% nitric-hydrochloric acids (v/v ) and concentrated nitric-hydrochloric acids (1:1). NIST SRMs 1648, 1579a, 2583, 2704, 2710, 3087a, and 8074 were subjected to these acid conditions a nd ultrasonic energy (about 1 W cm(-2)), and elemental recoveries were dete rmined following analysis by inductively coupled plasma atomic emission spe ctrometry (ICP-AES). Observed recoveries were higher overall with HNO3-HCl mixtures than with nitric acid alone, and recoveries were generally higher for concentrated acid mixtures. Recoveries of > 80% could be achieved for s ome elements (As, Cd, Cu, Mn, Pb, Zn) when using acidic ultrasonic treatmen t with no deliberately added heating, even under diluted acid conditions. H owever, several elements (Ba, Co, Cr, Fe, Mg, Ni, V) yielded v 75% recoveri es when using sonication without deliberate heating, even in concentrated H NO3-HCl. For comparison with UE, selected SRMs were subjected to acid leach ing (no sonication) in the above acid solutions. Elemental recoveries from acid leaching without sonication were generally lower overall when compared to results obtained from UE, thereby demonstrating the effect of ultrasoun d for the dissolution of target analytes. Sonication of chromate-containing certified reference materials and certified filter samples (European Commi ssion Certified Reference Material 545) in slightly basic buffer solutions was shown to be effective for the complete ( 90%) dissolution of hexavalent chromium (Cr-VI) from both soluble (potassium chromate) and insoluble (lea d chromate) Cr-VI reference sources. Sonication in HNO3-HF was used to extr act Cd, Fe, Pb and Zn from aerosol filters, water rinsates and aerosol samp lers alone; ICP-AES was used for elemental measurement. Sample losses were found for these four elements from rinsates and samples following removal o f the aerosol filter, thereby demonstrating the utility of carrying out son ication directly within the aerosol sampler containing the filter. It is hy pothesized that UE will be increasingly used for analytical sample preparat ion purposes.