Microwave-assisted extraction of rare earth elements from petroleum refining catalysts and ambient fine aerosols prior to inductively coupled plasma-mass spectrometry
Abstract A robust microwave-assisted acid digestion procedure followed by inductively coupled plasma-mass spectrometry (ICP-MS) was developed to quantify rare earth elements (REEs) in fluidized-bed catalytic cracking (FCC) catalysts and atmospheric fine particulate matter (PM2.5). High temperature (200 ◦C), high pressure (200 psig), acid digestion (HNO3, HF and H3BO3) with 20 min dwell time effectively solubilized REEs from six fresh catalysts, a spent catalyst and PM2.5. This method was also employed to measure 27 non-REEs including Na, Mg, Al, Si, K, Sc, Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Zr, Mo, Cd, Cs, Ba, Pb and U. Complete extraction of several REEs (Y, La, Ce, Pr, Nd,Tb, Dy and Er) required HF indicating that they were closely associated with the aluminosilicate structure of the zeolite FCC catalysts. Internal standardization using 115In quantitatively corrected non-spectral interferences in the catalyst digestate matrix. Inter-laboratory comparison using ICP-optical emission spectroscopy (ICP-OES) and instrumental neutron activation analysis (INAA) demonstrated the developed analytical method for accurate analysis of REEs in FCC catalysts. The method developed for FCC catalysts was also uccessfully implemented to measure trace to ultra-trace concentrations of La, Ce, Pr, Nd, Sm, Gd, Eu and Dy in ambient PM2.5 in an industrial area of Houston,TX.
Microwave-assisted extraction through an aqueous medium and simultaneous cleanup by partition on hexane for determining pesticides in agricultural soils by gas chromatography: A critical study
Abstract Asimple microwave-assisted extraction and partitioning method (MAEP) usingwater–acetonitrile and n-hexane for desorption and simultaneous partitioning, respectively, together with gas chromatography (GC) was studied to determine representative pesticides (trifluralin, metolachlor,chlorpyriphos and triadimefon) with a broad range of physico-chemical properties in agricultural soils. Three points were considered crucial in this study: instrumental and sample-associated factors affecting extraction of the target compounds were studied through experimental design; the spiking procedure at trace levels was carried out to reproduce the solute-soil sorption taking place in the environment as closely as possible; and results were analyzed taking into account the adsorption behaviour of the compounds on different kinds of soils. The complete analytical procedure proposed consisted of the MAEP of pesticides from 1.0 g of soil with 1mL of 1:1 water/acetonitrile mixture, and 5mL of hexane for trapping.The microwave heating program applied was 2 min at 250Wand 10 min at 900W, and 130 ◦C maximum temperature. After extraction, the hexane layer was evaporated to dryness; the residue was re-dissolved and directly analyzed by gas chromatography electron capture detection (GC-ECD).Clean chromatograms were obtained without any additional cleanup step. Besides the four pesticides used to optimise MAEP, the method was applied to determine an additional group of pesticides (triallate, acetochlor, alachlor, endosulphan I and II, endrin, methoxychlor and tetradifon) in different soils. Most of the compounds studied were recovered in good yields with relative standard deviations (R.S.D.s) below 9% and detection limits ranged from 0.004 to 0.036 g g−1. The described method is efficient and fast to determine hydrophobic pesticides at ng g−1 level in soil with different clay-to-organic matter ratios.
Optimization of a microwave-assisted extraction large-volume injection and gas chromatography–ion trap mass spectrometry procedure for the determination of polybrominated diphenyl ethers, polybrominated biphenyls and polychlorinated naphthalenes in sediments
Abstract A sensitive and rapid method for the determination of polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs) and polychlorinated naphthalenes (PCNs) in sediment samples is proposed. The method involving microwave-assisted extraction (MAE) and large-volume injection (LVI) gas chromatography (GC)–ion trap mass spectrometry (ITMS), and the experimental conditions were optimized using the statistical design of experiments (DOE).
A Plackett–Burman (P–B) design was chosen to estimate the influence of five factors, such as resonance excitation voltage (EV), isolation time (IT), excitation time (ET), ion source temperature (IST) and electron energy (EE) on the analytical response in the ITMS determination.
In order to increase the analytical response, 70 L of the final extract were injected into the GC–tandem mass spectrometry (MS–MS) using a programmable temperature vaporizer (PTV). The factor settings involving injection temperature, vaporization temperature, vaporization time and flow during the evaporation step were previously optimized using a central composite design (CCD).
The MAE was carried out using the hexane–acetone (1:1, v/v) mixture and the extraction conditions were optimized with a CCD. The highest response was obtained with a volume of 48 mL, a temperature of 152 ◦C and an extraction time of 24 min. The optimized method gives recoveries between 75 and 95% with relative standard deviations (R.S.D.) that ranged from 4 to 13%. The limit of detection (LOD) ranged between 4 and 20 pg g−1 dry weight (dw) when 5 g of sediment were analyzed. The MAE method was applied to the analyses of polyhalogenated compounds in sediments collected in the harbour of Valencia (Spain).
The proposed method may serve as an alternative for GC–negative chemical ionization (NCI)–MS and can be used in government testing programmes.
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