Amauri A. Menegário

Determination of Ba, Cd, Cu, Pb and Zn in saliva by isotope dilution direct injection inductively coupled plasma mass spectrometry.

Trace elements in small sample volumes of saliva were determined by coupling a high efficiency direct injection nebulizer to inductively coupled plasma mass spectrometry and employing quantification by isotope dilution. Aliquots of 0.4 ml of human saliva were mixed with 0.1 ml of concentrated nitric acid and diluted to 2 ml with water. Sample solutions were spiked with an isotopic solution enriched in 135Ba, 112Cd, 65Cu, 206Pb and 66Zn. The amount of each isotope added to the samples and the measurement procedure were adjusted to attain precise analytical results calculated from the isotope ratios 135Ba/138Ba, 112Cd/114Cd, 65Cu/63Cu, 206Pb/208Pb and 66Zn/68Zn. Data acquisition for Ba, Cu and Zn isotopes was performed for a single sample injection of 50 microl and in another sample injection the Cd and Pb isotopes were measured. Concentrations ranging from 5.0 to 16 microg l(-1) for Ba, from 0.50 to 1.1 microg l(-1) for Cd, from 6.0 to 50 microg l(-1) for Cu, from 0.8 to 18.8 microg l(-1) for Pb and from 46.0 to 230 microg l(-1) for Zn were found in saliva samples. Detection limits of 0.11, 0.03, 0.40, 0.05 and 0.59 microg l(-1) were determined for Ba, Cd, Cu, Pb and Zn, respectively. The concentrations found by isotope dilution were in agreement with those of the completely digested samples quantified by external calibration. The direct analysis of 30 samples per hour was attained with the proposed procedure, avoiding time-consuming digestion steps, contamination risks and matrix effects.

Rapid sequential determination of arsenic and selenium in waters and plant digests by hydride generation inductively coupled plasma-mass spectrometry

Abstract A synchronised flow system with hydride generation coupled to ICP-MS is proposed for the sequential determination of As and Se in natural waters and plant digests. The alternated mixing of the sample solution with thiourea or HCl for the determination of As or Se under optimized conditions was achieved using a flow commutator before the reaction with NaBH 4 . The on-line addition of thiourea promoted the quantitative reduction of As(V) to As(III), thus enhancing sensitivity and precision. The selenium pre-reduction from Se(VI) to Se(IV) was produced by heating the sample with HCl, and the hydride generation was performed in 4 mol l −1 HCl, thus avoiding interference from thiourea. The system allowed the analysis of 20 samples h −1 with LOD values of 0.02 μg l −1 As and 0.03 μg l −1 Se. Results were in agreement with the certified values at the 95% confidence level for reference waters from the Canadian National Water Research Institute and plant samples from the National Institute of Standards and Technology (NIST).

On-line electrolytic dissolution of alloys in flow injection analysis. Determination of iron, tungsten, molybdenum, vanadium and chromium in tool steels by inductively coupled plasma atomic emission spectrometry

A flow injection procedure involving on-line anodic electrolytic dissolution for Fe, W, Mo, V and Cr determination in tool steels by inductively coupled plasma atomic emission spectrometry is proposed. The sample is dissolved in an electrolytic cell coupled to the spectrometer nebulizer and a 1.5 mol l 1 HNO3 electrolytic solution is used to close the electric contact between electrodes. The system permits direct analysis of 30 solid samples per hour (150 determinations) and yields results with a relative standard deviation (r.s.d) lower tha n5%( n D 5). The applicability of the procedure was verified by analyzing tool steels samples and accuracy was assessed by comparison with a conventional sample dissolution procedure. ©2000 Elsevier Science B.V. All rights reserved.

On-line electrolytic dissolution for lead determination in high-purity copper by isotope dilution inductively coupled plasma mass spectrometry

Abstract A flow injection system combining electrolytic dissolution (ED) and programmable isotope dilution (ID) for determination of lead in high-purity copper by inductively coupled plasma mass spectrometry (ED-ID-ICP-MS) is proposed. ED was performed employing a Teflon chamber in where a gold cathode was placed. Best electrolytic conditions were achieved by using an 1.5xa0molxa0L−1 nitric acid as electrolytic solution and applying 2.5xa0A (dc) current during 4xa0s. Lead was determined in the electrolytic dissolved sample, which has undergone on-line isotope dilution exploiting binary sampling approach. Isotope dilution was carried out measuring the isotope ratio 206 Pb / 208 Pb before and after on-line addition of the 208 Pb -enriched solution. Precision of isotope ratio measurements for a sample containing 7–70xa0μgxa0Pbxa0g−1 was characterized by relative standard deviation (R.S.D.) of 0.5% (n=3) and the proposed methodology presented an R.S.D. lower than 4% (n=9). Accuracy was assessed comparing obtained results with those obtained by conventional dissolution and no significant difference at 95% confidence level was observed.

On-line preconcentration flow system for multi-elemental analysis by total reflection X-ray fluorescence spectrometry

Abstract A scaled-down preconcentration flow system coupled with total reflection X-ray fluorescence spectrometry is proposed for the simultaneous determination of Co, Cu, Mn, Ni, Pb and Zn. The flow system, assembled with an 11-μl column of AG50W-X8 resin and three-way solenoid valves commanded by a computer program, permits the automatic preconcentration, addition of internal standard (Ga) and the deposition of the eluate on the reflector plate. Interferences due to Na and Ca were evaluated. When compared with conventional flow systems, the proposed approach allows a significant reduction in the consumption of eluent (200 μl per determination) and only 1075 μl of sample is required to obtain enrichment factors of approximately 20. Detection limits of Co, Cu, Mn, Ni, Pb and Zn were improved 11, 13, 13, 12, 17 and 14 times, respectively. The proposed system was applied to analyze human saliva and river water samples. Analysis of a Natural Water Standard Reference Material-1640 (Natural Institute of Standard and Technology) showed excellent agreement with certified values. The recoveries for Co, Cu, Mn, Ni, Pb and Zn in a spiked saliva sample were between 64 and 108%.

Micro-scale flow system for on-line multielement preconcentration from saliva digests and determination by inductively coupled plasma optical emission spectrometry

A micro-scale flow system is proposed for on-line preconcentration of Cd, Cu, Mn, Ni and Pb in saliva samples and their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). A small column containing 8 μl of AG50W-X8 resin was inserted into the flow system, assembled with capillary tubes and connected to a micro-concentric nebulizer. The elution of the analytes was performed with 3 mol l−1 HCl at a flow rate of 82 μl min−1. The ICP-OES signal acquisition program permits measurements for 5 s in the concentrated portion of the transient elution peaks. A sample volume of 1 ml was required to obtain enrichment factors of 46, 23, 17, 18 and 44 for Cd, Cu, Mn, Ni and Pb, respectively. The relative standard deviations for a 50-μg l−1 multi-analyte solution were ≤6.5%. The recoveries for Cd, Cu, Mn, Ni and Pb in digested human saliva samples were between 86 and 111%. The sample throughput was 24 h−1.

Boron isotope dilution in cellular fractions of coffee leaves Evaluated by Inductively Coupled Plasma Mass Spectrometry with direct injection nebulization (DIN-ICP-MS)

A diluicao isotopica do B enriquecido em 94,14 atomos % em 10B fornecido durante o cultivo de mudas de cafeeiro foi avaliada na parede celular, nucleo e cloroplastos de celulas foliares. Para isto foi necessaria a determinacao de 11B/10B em pequenos volumes de amostras conseguidas pelo processo de fracionamento por centrifugacao diferenciada. As determinacoes isotopicas foram efetuadas por espectrometria de massas com fonte de plasma acoplado indutivamente (ICP-MS) utilizando-se nebulizador de injecao direta (DIN). Razoes isotopicas de B entre 1,002 e 1,326 foram determinadas em 50 mL das amostras enriquecidas com precisao caracterizada por RSD<1,5%. As concentracoes de B encontradas nas fracoes celulares variaram entre 3,3 e 10,8 mg g-1, e em media os atomos % de 10B foram 46,7; 44,5 e 48,8 na parede celular, nucleo e cloroplasto, respectivamente. O limite de deteccao foi estimado em 0,5 ng B mL-1.

Micro flow system to perform programmable isotope dilution for inductively coupled plasma-mass spectrometry

Abstract A flow system using computer controlled devices to implement binary sampling of small volumes of sample and spike solutions was coupled to an inductively coupled plasma-mass spectrometer to perform programmable isotope dilutions. A computer running software in QuickBasic controlled the time-based sampling of sample and spike solution by switching on/off a set of solenoid valves. Mixing was improved by sampling 15 small aliquots of both solutions at a flow-rate of 65xa0μlxa0min−1 through a capillary tubing connected to a micro-concentric nebulizer (MCN). Each aliquot of 6xa0μl containing the sample plus spike was introduced during 4xa0s. Programming the sample to spike volumetric ratios in each aliquot allowed to perform different isotopic dilutions generated from a single enriched solution. The flow system was calibrated measuring the isotopic ratios of 112 Cd / 114 Cd by binary sampling of natural abundance Cd solutions as sample and enriched 112 Cd (97xa0at.%) solution as spike. The programmed and the measured ratios in the range from 6 to 25 presented good correlation (0.997). For routine analysis, using an estimate analyte concentration, and the isotope ratio within the defined range, the software calculates the time delays to introduce the sample and spike volumes. The true and found concentrations for solutions containing from 2.0 to 20.0xa0μgxa0l−1 Cd attained good agreement at the 95% of confidence level. For these solutions the consumption of enriched 112 Cd (97xa0at.%) ranged from 33 to 168xa0pg per determination. About 30 isotope dilutions per hour were achieved.

Boron isotope ratios in plants enriched in 10B as determined by direct injection nebulization inductively coupled plasma mass spectrometry

The determination of boron (B) isotope ratios (11B/10B) in small amounts of 10B enriched cotton plants was performed by inductively coupled plasma mass spectrometry (ICP-MS) with direct injection nebulization (DIN). Boron isotope ratios were determined in 1.0 M hydrochloric acid (HCl) extracts and in total digests produced by high pressurized microwave oven. Both procedures resulted in contaminants free solutions, without losses of B and with low carbon (C) residues. Small sample volumes (50 μL) were introduced by DIN into the plasma, reducing memory effects and allowing 45 determinations hr−1. Instrumental mass biases from −1.00–4.66% were found for solutions with 10B isotopic compositions ranging from 20–70 atom %. Isotopic ratios from 1.091–1.834 were determined with precision characterized by RSD<1.4% for samples with B concentration ranging from 15–50 μg g−1. The detection limit was 0.4 ng B mL−1. Boron isotope ratios determined by both procedures were in agreement at the 95% confidence level.

Eletrodissolução de ligas de latão empregando sistemas de análise em fluxo para a determinação de cobre, zinco e chumbo por ICP-AES

An on-line electrodissolution procedure implemented in a flow injection system for determination of copper, zinc and lead in brasses alloys by ICP-AES is described. Sample dissolution procedure was carried out by using a PTFE chamber and a DC power supply with constant current. Solid sample was attached to chamber as anode and a gold tubing coupled in the chamber was used as cathode. An electrolytic solution flowing through the gold tubing closed the electric circuit with sample, in order to provide condition for electric dissolution when the DC power supply was switched on. The best results were achieved by using a 1.5 mol l-1 nitric acid solution as electrolyte and a 2.5 A current intensity. The procedure presented a good performance characterized by a relative standard deviation better than < 5% (n=5) and a sample throughput of 180 determinations per hour for Cu, Zn and Pb. Results were in agreement with those obtained by conventional acid dissolution (99% confidence level).