Raquel C. Machado

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.

Strategy of Sample Preparation for Arsenic Determination in Mineral Fertilizers

A method for determination of arsenic in mineral fertilizers by continuous flow hydride generation atomic absorption spectrometry (CF-HG-AAS) was developed by using diluted acid and digester block with perfluoroalkoxy (PFA) tubes to sample preparation. An additional sample preparation procedure using microwave-assisted digestion was evaluated and compared with the proposed procedure. A full factorial design was applied to investigate the effect of the variables and the best conditions found were 7 mol L−1 HNO3 + 30% (m/m) H2O2 as reagents, 4 h of digestion and concentration of reagents diluted 1:1. The effect of concomitants on the analytical signal of arsenic was investigated and no one significant interference was observed, with recoveries ranged from 97 to 103%. The accuracy of proposed method was evaluated by certified reference material (NIST SRM 695) and recovery of 95% was obtained. The arsenic concentration (8.9 ± 0.2 mg kg−1) found in the fertilizer is below of maximum concentration established by Brazilian legislation.

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.

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.

Multielemental Determination of As, Bi, Ge, Sb, and Sn in Agricultural Samples Using Hydride Generation Coupled to Microwave-Induced Plasma Optical Emission Spectrometry

A microwave-induced plasma optical emission spectrometer with N2-based plasma was combined with a multimode sample introduction system (MSIS) for hydride generation (HG) and multielemental determination of As, Bi, Ge, Sb, and Sn in samples of forage, bovine liver, powdered milk, agricultural gypsum, rice, and mineral fertilizer, using a single condition of prereduction and reduction. The accuracy of the developed analytical method was evaluated using certified reference materials of water and mineral fertilizer, and recoveries ranged from 95 to 106%. Addition and recovery experiments were carried out, and the recoveries varied from 85 to 117% for all samples evaluated. The limits of detection for As, Bi, Ge, Sb, and Sn were 0.46, 0.09, 0.19, 0.46, and 5.2 μg/L, respectively, for liquid samples, and 0.18, 0.04, 0.08, 0.19, and 2.1 mg/kg, respectively, for solid samples. The method proposed offers a simple, fast, multielemental, and robust alternative for successful determination of all five analytes in agricultural samples with low operational cost without compromising analytical performance.

Multi-energy calibration as a strategy for elemental analysis of fertilizers by microwave-induced plasma optical emission spectrometry

Multi-energy calibration (MEC) was applied for the determination of As, Ba, Cd, Cr, and Pb in fertilizer samples by microwave-induced plasma optical emission spectrometry. Commercial fertilizer samples and a certified reference material of mineral fertilizer (CRM NIST 695) were digested using microwave-assisted acid. The MEC approach was carried out using only two calibration solutions: S1, composed of 50% v/v digested sample and 50% v/v standard reference solution containing the analytes, and S2, composed of 50% v/v sample and 50% v/v blank solution. The accuracy of the method was evaluated by analyzing CRM NIST 695, with recoveries in the 96–101% range. Addition and recovery experiments were also carried out for Cd determination, with recoveries between 92 and 105% for the evaluated samples. The MEC strategy was compared with traditional external standard calibration and standard additions methods and was the only one to provide accurate results for all evaluated analytes.