Determination of rare earth elements in graphite by solid sampling electrothermal vaporization-inductively coupled plasma mass spectrometry

Abstract

A method is proposed for the determination of trace rare earth elements (REEs) in graphite by solid sampling electrothermal vaporization-inductively coupled mass spectrometry (ETV-ICP-MS). The operating parameters of the ETV system such as gas flow-rate, heating program, the use of a modifier gas (Freon R-12) as well as sample mass were evaluated. The determination of REE in graphite samples was performed by directly weighing a solid sample (0.5 to 2.5 mg) on the graphite platform of the ETV system. Calibration was carried out using aqueous standards. According to the results, the presence of the modifier gas (Freon R-12) promoted an enhancement of vaporization for all analytes, besides the reduction of the vaporization temperature (about 500 C lower). The accuracy was evaluated by an analyte recovery experiment and also by comparison of results with those obtained by microwaveassisted extraction (MAE) with further determination of REE by ICP-MS equipped with an ultrasonic nebulizer (USN-ICP-MS). Agreement was observed between the results obtained by ETV-ICP-MS and MAE with USN-ICP-MS analysis for most of the elements. Analyte recovery ranged from 100.3 to 118.7% and the obtained RSDs were always lower than 24%. The limits of detection were at the ng g À1 level and were similar to those obtained by USN-ICP-MS with previous sample preparation by MAE. The proposed method was suitable for direct determination of REE in graphite. In addition, direct analysis of graphite by ETV-ICP-MS avoided the laborious sample preparation step of graphite and the use of concentrated acids for digestion, minimizing interferences in the determination step by ICP-MS.

Feasibility of Rare Earth Element Determination in Low Concentration in Crude Oil: Direct Sampling Electrothermal Vaporization-Inductively Coupled Plasma Mass Spectrometry

“…Pyrolytic-coated graphite tubes and graphite platforms (both from Spectral Systems) were used. A homemade electronic controller was developed and used for commanding a three-way solenoid pinch valve (positioned between the ETV system and the ICP torch) and also to allow the flow the Freon R-12 (CCl 2 F 2 ), as described in previous work . A microbalance (M2P, Sartorius, Germany, 1 μg of resolution) was used for sample weighing.…”

“…In this study, 16 nuclides were monitored, and a selection of REE nuclides was performed to achieve a compromise condition to select the most abundant and less susceptible nuclide to polyatomic interferences (Table S-1). − , The Ar dimer ( 78 Ar 2 + ) was monitored during the acquisition of the analytical signals to evaluate the plasma stability. ,, The modifier gas (Freon R-12), the carrier gas and bypass gas flow rates were evaluated over the ranges of 1.0–6.0 mL min –1 , 0.10–0.60 L min –1 , and 0.10–0.60 L min –1 , respectively.…”

“…Electrothermal vaporization-inductively coupled plasma mass spectrometry (ETV-ICP-MS) has been used for the determination of REE in several matrices, since it allows sample introduction with a minimum pretreatment, reducing reagent consumption, mainly by avoiding the use of concentrated acids, and the generation of residues. − Another advantage of ETV-ICP-MS is the possibility of obtaining low LOQs (in the ng g –1 range) since it combines the good sensitivity of ICP-MS technique with the direct sampling by ETV, which has higher transport efficiency (20–80%) than pneumatic nebulization (1–5%). ,− It is important to notice that the aerosol formed in the electrothermal vaporizer is a dry vapor, minimizing spectral interferences from the formation of oxides and hydroxides in the determination of REE by ICP-MS. ,, Some limitations of ETV system have been reported for calibration step and sample representativeness. Low-sample masses (0.1–5 mg) are generally used. , However, matrix effects can sometimes hamper the calibration with aqueous reference solutions. − , These limitations can be overcome by optimizing the operating conditions of the ETV system, such as the heating program, the gases flow rate, the use of modifiers and the sample amount. ,,− Another limitation of the use of ETV system is related to the need of a high degree of the analyst’s know-how to develop a method. , On the other hand, after optimization, the application of ETV-ICP-MS method requires the same degree of analyst training of a method based on ICP-MS technique using pneumatic nebulization. ,, …”

An ultrasound‐assisted sample preparation method of carbonatite rock for determination of rare earth elements by inductively coupled plasma mass spectrometry

“…Spectrometric techniques, such as atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP‐OES) or X‐ray fluorescence (XRF), can suffer from relatively poor sensitivity and require the separation of these elements before their determination to avoid spectral interference. Inductively coupled plasma mass spectrometry (ICP‐MS) presents several advantages for the determination of REEs, such as the multi‐elemental capacity, the high sensitivity, the low detection limits, the wide calibration range and the high precision . However, suitable methods for sample dissolution for sample introduction into ICP‐MS instruments are critical.…”

“…However, suitable methods for sample dissolution for sample introduction into ICP‐MS instruments are critical. The sample solutions introduced into the ICP‐MS system must have a low dissolved solids and organic materials content, and care must be taken with the composition of these solutions to avoid interferences …”