Clarice D.B. Amaral

Sample preparation for arsenic speciation in terrestrial plants—A review

Arsenic is an element widely present in nature. Additionally, it may be found as different species in several matrices and therefore it is one of the target elements in chemical speciation. Although the number of studies in terrestrial plants is low, compared to matrices such as fish or urine, this number is raising due to the fact that this type of matrix are closely related to the human food chain. In speciation analysis, sample preparation is a critical step and several extraction procedures present drawbacks. In this review, papers dealing with extraction procedures, analytical methods, and studies of species conservation in plants cultivated in terrestrial environment are critically discussed. Analytical procedures based on extractions using water or diluted acid solutions associated with HPLC-ICP-MS are good alternatives, owing to their versatility and sensitivity, even though less expensive strategies are shown as feasible choices.

Determination of P, S and Si in biodiesel, diesel and lubricating oil using ICP-MS/MS

The feasibility of inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) to overcome polyatomic interferents in severely affected isotope determination is demonstrated here. This instrument arrangement presents an octopole reaction/collision system (ORS) in between two quadrupole mass analyzers. The first quadrupole operates as a mass filter which allows just the target mass-to-charge ratio (m/z) to enter the ORS and rejects all other species with m/z different from the target analytes m/z. Once in the ORS, analytes react with the reaction gas introduced into the ORS, and the second quadrupole selects the product of the reactions m/z (mass shift operation mode). We describe here a procedure for accurate determination of P, S and Si in biodiesel, diesel and lubricating oil by ICP-MS/MS. Fuel standard reference materials (SRMs) were microwave-assisted acid-digested using nitric acid and hydrogen peroxide. The oxygen gas flow rate in the ORS was optimized considering the limit of detection (LOD) values and accuracies reached for P, S and Si determinations in the lubricating oil SRM and the best oxygen gas flow rate was 0.75 mL min−1. Adopting optimized conditions, limits of detection were 1.2, 0.49, 0.31, 0.33 and 0.78 μg L−1 for 28Si16O+, 29Si16O+, 31P16O+, 32S16O+ and 34S16O+, respectively. Adequate precision, accuracy and sensitivity were obtained when using the mass shift mode and recoveries for biodiesel, diesel and lubricating oil digests ranged from 95.0 to 113%. No significant differences were observed between the certified values and the ones obtained using ICP-MS/MS at a 95% confidence level.

A novel strategy to determine As, Cr, Hg and V in drinking water by ICP-MS/MS

This work demonstrates the potential of inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) in trace element analysis. Aiming Hg determination in water, sample preservation requires chloride addition, which presents formation of polyatomic interfering ions as a drawback for the determination of other analytes (e.g. As and V). Thus, the effect of chloride on As, Cr, V and Hg determination and the feasibility of using ICP-MS/MS to circumvent the interference were evaluated. A standard reference material (NIST SRM 1643e) and recoveries from tap water spiked with As, Cr, Hg and V were used for accuracy assessment and for the evaluation of matrix effects. The reaction between Hg and oxygen gas is not favorable in the octopole reaction system (ORS3). Therefore, Hg was accurately determined as a single atom ion (202Hg+) under the same analytical conditions adopted for As, Cr and V determination by monitoring 75As16O+, 52Cr16O+ and 51V16O+ while the ORS3 was pressurized with oxygen gas. The oxygen reaction mode significantly improved the accuracy for As, Cr and V, especially at the lowest spiked level, which is strongly affected by matrix effects. The signal gain in m/z 75 for a solution containing 1 μg L−1 As in 0.48 mol L −1 chloride medium was 1974% when employing single quadrupole mode. On the other hand, the signal increased only 7% when 0.75 mL min−1 O2 was used in mass shift mode proving the efficiency of the MS/MS mode. Thus, ICP-MS/MS and ORS3 pressurized with O2 gas effectively reduced the interference, and enhanced the accuracy and sensitivity for some specific isotopes in a complex medium. The limits of detection for V (51V16O+), Cr (52Cr16O+), As (75As16O+) and Hg (202Hg+) were estimated to be 2, 3, 1.6 and 38 ng L−1 at the 99.7% confidence level, respectively.

Evaluation of Inductively Coupled Plasma Tandem Mass Spectrometry for Determination of As in Agricultural Inputs with High REE Contents

In the present work, an inductively coupled plasma-tandem mass spectrometer (ICP-MS/MS) operating in single quadrupole and mass shift modes were evaluated for As determination in mineral fertilizers and agricultural gypsum with high contents of rare earth elements. For MS/MS mode, oxygen was the gas introduced into the octopole reaction system (ORS3). Samples were prepared by microwave-assisted digestion with diluted nitric acid solution. The accuracy was checked by analysis of a fertilizer certified reference material (NIST SRM 695) and by addition and recovery experiments. When operating in single quadrupole mode, recoveries ranged from 59 to 151%; while values obtained by MS/MS mode varied from 81 to 105% when 0.30 mL min-1 O2 was introduced into the ORS3. Limits of detection for As+ in single quadrupole and AsO+ in MS/MS mass shift mode were 6 and 9 ng L-1, respectively.

Aerosol dilution as a simple strategy for analysis of complex samples by ICP-MS

This study investigated the capability of High Matrix Introduction (HMI) strategy for analysis of dialysis solution and urine samples using inductively coupled plasma mass spectrometry. The use of HMI enables the direct introduction of urine samples and dialysis solutions 2-fold diluted with 0.14molL-1 HNO3. Bismuth, Ge, Ir, Li, Pt, Rh, Sc and Tl were evaluated as internal standards for Al, Ag, As, Be, Cd, Cr, Pb, Sb, Se, Tl, and Hg determination in dialysis solution and As, Cd, Hg and Pb determination in urine samples. Helium collision cell mode (4.5mLmin-1) was efficient to overcome polyatomic interferences in As, Se and Cr determinations. Mercury memory effects were evaluated by washing with 0.12molL-1 HCl or an alkaline diluent solution prepared with n-butanol, NH4OH, EDTA, and Triton X-100. This later solution was efficient for avoiding Hg memory effects in 6h of analysis. Linear calibration curves were obtained for all analytes and detection limits were lower than maximum amounts allowed by Brazilian legislations. Recoveries for all analytes in dialysis solutions and urine samples ranged from 82% to 125% and relative standard deviations for all elements and samples were lower than 7%. Analysis of control internal urine samples was in agreement with certified values at 95% confidence level (t-test; p < 0.05).

Critical evaluation of internal standardization in ICP tandem mass spectrometry and feasibility of the oxygen reaction for boron determination in plants

The feasibility of internal standardization and the oxygen reaction in ICP-MS was studied for accurate determination of boron. Lithium, Be and Rh were systematically evaluated as internal standards (I.S.) for B determination in plants by ICP-MS/MS using a single quadrupole mode and MS/MS mode with O2 into a cell, where B and internal standard signal intensities were processed either after both or only one of them reacted. Carbon is a source of spectral and matrix interferences in B determination by ICP-MS. The use of instrumental strategies such as tandem mass spectrometry (MS/MS) concomitantly with internal standardization demands further investigation about the I.S. behaviour regarding the gas phase reaction with oxygen. The behaviours of B and Be, as well as their oxides, were quite similar in an octopole reaction system containing O2. The coexistence of spectral and non-spectral interferences was evidenced by increasing carbon concentrations in samples and checking positive errors caused for 11B+. Recoveries for B determination in plant certified reference materials without I.S. ranged from 98 to 145% and with Be as an internal standard ranged from 98 to 108%. Beryllium presented favourable characteristics as an internal standard for B due to its mass closeness, similar ionization energy, and reactivity with oxygen.

Investigation of analyte losses using microwave-assisted sample digestion and closed vessels with venting

Microwave-assisted sample digestion using closed vessels is becoming the standard for trace analysis because contamination and losses can be better controlled. Gases are generated during digestion and there is an increment of the internal vessel pressure. Consequently, vessels venting may occur depending on the design of the vessel and the maximum pressure it can stand for. In the present work it was observed that it is possible to allow venting during the digestion without losing volatile analytes, such as As, when properly controlling heating and chemical conditions. Recoveries for As in certified reference materials of animal tissues ranged from 94 to 112% despite mass losses as high as 62%mm(-1) observed in the digests. However, for Hg(II) in medium containing chlorides recoveries were poor. The efficiency of digestion was measured by determination of organic carbon contents in digests and they ranged from 0.10 to 0.19% for plant and animal tissues. The temperature gradient along the vessel height is important for avoiding losses of volatile elements.

Determination of Elemental Impurities in Acyclovir Ointment and Raw Materials Using Microwave Acid Digestion (MW-AD) and ICP-MS

Inorganic elements present in pharmaceutical products were determined by inductively coupled plasma-mass spectrometer (ICP-MS), employing microwave acid digestion as a sample preparation method. The most abundant isotopes, 75As+ , 65Cu+ , 52Cr+ , 58Ni+ , 208Pb+ , and 51V+ , were determined in acyclovir ointment and its constituents. Elemental impurities in the pharmaceutical samples were determined using an inductively coupled plasma-universal cell technology-mass spectrometer (ICP-UCT-MS) operated in kinetic energy discrimination (KED) and standard mode. The accuracy of the method was assessed by means of addition and recovery experiments. Except for Cr, spiked recoveries of the elements added to the samples before microwave acid digestion (MW-AD) step were between 95.1 and 126%, and after MW-AD step ranged from 85.6 to 132%. Limits of detection (LOD) obtained by proposed method is in agreement to those required by the U.S. Pharmacopeia Convention (USP), showing that the ICP-MS technique is well suited for quantification of these elements. The LOD?s (ng L-1) for 51V+ , 52Cr+ , 58Ni+ , 65Cu+ , 75As+ and 208Pb+ in 1% v v-1 HNO3 medium were: 2.2, 81.3, 91.9, 6.9, 0.2 and 3.1, respectively. The concentration of the analytes in these samples presented a wide range, varying from 2.3 ± 0.8 µg kg-1 for As to 3446 ± 47 µg kg-1 for Cr.

Characterization of Synchronous Vertical Dual View Inductively Coupled Plasma Optical Emission Spectrometer with Application for Water Analysis

ABSTRACT The performance of an inductively coupled plasma optical emission spectrometer was evaluated using Ar, Ba, Mg, and Ni as test elements. Short- and long-term stabilities were excellent with relative standard deviations lower than 2%. The warm-up times in axial, radial, and synchronous vertical dual view (SVDV) modes were 2 min. The limits of detection and quantification for As, Ba, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, and U were evaluated and the values were compatible with Brazilian and the US Environmental Protection Agency legislation for potable water. A standard reference material of trace elements in water (SRM 1643e) was used to verify the accuracy for As, Ba, Cd, Cr, Cu, Ni, Pb, Sb, and Se in axial and SVDV. Both configurations provided suitable accuracy and sensitivity. The elements were successfully determined in three bottled commercial drinking water and in two fortified samples using SVDV.

Determination of selenium in bovine semen by ICP-MS using formic acid for sample preparation.

Determination of Se by inductively coupled plasma mass spectrometry (ICP-MS) can be difficult due to spectral interferences; however, these interferences can be eliminated by using collision-reaction interface (CRI) technology. A simple and fast procedure for determination of total Se concentration in bovine semen by ICP-MS after sample solubilization with diluted formic acid is here proposed. Formic acid caused an increase of up to 50% in selenium net signals and the maximum gain was obtained at 10% v v-1 formic acid solution. The optimized nebulizer gas flow rates were 1.05 and 0.95 L min-1, and radio frequency applied power were 1.3 and 1.4 kW without and with CRI, respectively. Microwave-assisted acid digestion was also implemented in the preparation of semen sample for comparison of results. No statistical differences between these sample preparation strategies at 95% confidence level (t-test) were observed for 76Se+ , 77Se+ , 78Se+ and 82Se+ without using CRI and 82Se+ with CRI.