Influence of digestion procedures on the determination of rare earth elements in peat and plant samples by USN-ICP-MS

Abstract

Analytical procedures for the determination of rare earth elements (REE) in 250 mg aliquots of difficult-todigest peat and plant matrices by ICP-MS were developed. Three different pressurised digestion approaches were tested for this purpose, namely (i) closed vessel acid digestion on a hot-plate at 180 uC, (ii) digestion in a microwave high pressure autoclave at a temperature of 240 uC and (iii) high pressure ashing (HPA) at a temperature of 320 uC. Acid mixtures for digestion contained concentrated nitric acid (3-5 ml) alone or additions of hydrofluoric acid (HF) or tetrafluoroboric acid (HBF 4) at volumes of 0.05-1.0 ml. The selection of appropriate volumes of HF or HBF 4 was identified as a critical step in obtaining accurate results. For several reasons, HBF 4 is preferred in comparison with the normally used addition of HF for the destruction of siliceous matter in the samples investigated. The optimum acid mixture consisted of 3 ml of HNO 3 and 0.1 ml of HBF 4. High sample throughput (40 samples simultaneously in about 2 h) favours the microwave autoclave over the other two digestion systems. An ultrasonic nebuliser (USN) with membrane desolvation used for sample introduction reduced the spectral interferences originating from oxide formation of lighter REE and Ba to a negligible extent. Internal standardisation with Rh and Re proved to be essential for obtaining correct results. In this way, all REE could be reliably quantified by USN-ICP-MS without applying any mathematical correction equations. The accuracy of the optimised procedures was assessed by the determination of REE in digests of the certified reference material GBW 07602 Bush Branches and Leaves and of the candidate reference material CRM 670 Aquatic Plant. The developed analytical procedures were applied to the determination of REE in two different peat matrices. Results for these peat samples obtained by USN-ICP-MS showed good agreement with INAA values. Strong fractionation of REE caused by the addition of HF or HBF 4 in excess, known as lanthanide contraction, could be experimentally established, except for europium, which revealed a different behaviour.

Microwave-assisted extraction of rare earth elements from petroleum refining catalysts and ambient fine aerosols prior to inductively coupled plasma-mass spectrometry

“…Table 7, good agreement was observed for most of the elements (<20% RPD) in all catalysts. Similar to previous reports of REE analyses from peat, plant, rock, and rice, higher RPDs (>20%) were observed for Tb, Yb, and Lu [17,38]. Hence, care should be taken prior to report these three REEs from several matrices.…”

“…[17][18][19][20][21][22][23][24]. In contrast, FCC catalysts are anthropogenic, which are manufactured by incorporating REE cations in a zeolite support, and contain higher levels of siliceous matter.…”

Origin and fluxes of atmospheric REE entering an ombrotrophic peat bog in Black Forest (SW Germany): Evidence from snow, lichens and mosses

“…The lichen extremities are supposed to have grown recently and should have incorporated the most recent atmospheric material. Then lichens were crushed in a clean agate mortar before being digested 75 min at 240°C in a microwave autoclave with HNO 3 and HBF 4 as reagents, following the procedure described in Krachler et al (2002).…”

Periodic input of dust over the Eastern Carpathians during the Holocene linked with Saharan desertification and human impact

“…There is no riverine inflow, which means that inorganic material deposited within the bog is almost exclusively derived via direct atmospheric transport. The climate is temperate continental, with average annual temperatures of 15 • C and precipitation of 800 mm (Kristó, 1995). Surrounding vegetation is typical of this altitude in the Carpathians (Cristea, 1993), the bog being located at the upper limit of the beech forest, with spruce also found on surrounding slopes.…”

“…These samples were dried at 105 • C overnight before homogenising using a pestle and mortar and were then subjected to a mixed acid (HNO 3 : HCl: HF) total digestion (adapted from Krachler et al, 2002) for 40 min in a MARS accelerated reaction system. The solution was then analysed using a PerkinElmer Optima 8000 ICP-OES system at Northumbria University.…”