Ana Paula G. Gervasio

Cloud-point extraction of molybdenum in plants and determination by isotope dilution inductively coupled plasma mass spectrometry

Molybdenum in plant digests was accurately determined by cloud point extraction and quantification by isotope dilution inductively coupled plasma mass spectrometry. Plant digests spiked with 98Mo received 8-hydroxyquinoline and the surfactant Triton X-100, attaining an enrichment factor close to 70. The 98Mo/95Mo measurements were characterized by RSDs from 0.5 to 1%. Instrumental mass discrimination of 1.4% was experimentally determined and used to correct the results. Concentrations found in plant reference materials were in agreement at the 95% significant level with certified values. A limit of detection of 0.8 ng g−1 was calculated based on the blank uncertainties and calibration curve on both isotopes.

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.

Interfacing flow injection with capillary electrophoresis and inductively coupled plasma mass spectrometry for Cr speciation in water samples

A hyphenated system coupling flow injection (FI), capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed. Two interfaces were developed in order to couple all three systems: the first to couple FI to CE and the second to couple CE to ICP-MS. The first interface was a chamber with micro channels connecting the FI system to the electrophoresis capillary inlet. The capillary outlet was coupled to a concentric nebulizer in the ICP-MS by using the second interface with an electrolyte sheath flow and grounding electrode. Sample aliquots were sequentially introduced by the FI system with a few nanolitres being electrokinetically injected into the electrophoresis capillary in a reproducible manner. The system performed analysis of a continuous sequence of samples with no interruption of the applied voltage during sample replacement or column conditioning. The feasibility of this system was evaluated for Cr speciation. The separation time was improved by forming an anionic complex between Cr(III) and DTPA. Therefore, the analysis of both Cr species, Cr(III)-DTPA2− and CrO42−, attained compatible sample processing between CE and the interfaced techniques FI and ICP-MS. The anionic chromium species were separated in less than 2 min by applying 20 kV in a phosphate electrolyte with TTAOH (tetradecyltrimethylammonium hydroxide) as electroosmotic flow modifier adjusted to pH 8. The transient signals from both species monitored at m/z 53 were characterized by excellent resolution and precision. Peaks obtained using Cr(VI) and Cr(III) standard solutions with concentration ranging from 50 to 200 µg L−1 presented good correlation.

An improved flow-injection system for spectrophotometric determination of molybdenum and tungsten in tool steels.

A flow-injection procedure for simultaneous spectrophotometric determination of tungsten and molybdenum in steel alloys is proposed. The method exploits the catalytic effects of Mo(VI) and W(VI) on the rate of iodide oxidation by hydrogen peroxide under acidic conditions. A novel strategy for ion-exchange separation of the potential interfering species is proposed, and an AG50W-X8 cationic resin mini-column is used. The sample is injected twice, originating two sequential plugs, citrate being added to one of them in order to suppress the W(VI) catalytic activity thus providing the kinetic discrimination. The system handles 70 samples per hour and requires 1.6mg KI per determination. A linear response is verified up to 10mgl(-1) Mo (or W) in the injectate, and signal additivity is 98-103%. Results are precise (R.S.D.<0.04) and in agreement with ICP-OES. Running a standard reference material (IPT-50) assessed also accuracy.

Eletroforese capilar acoplada à espectrometria com plasma: uma ferramenta eficiente para a especiação

The most important features of the CE-ICP hyphenation, as well as its advantages and drawbacks as a tool for speciation are discussed. The fundamental principles of capillary electrophoresis and inductively coupled plasma mass spectrometry are also presented. Some applications involving different designs proposed in the literature to couple CE and ICP system for elemental speciation are reviewed.

Sistemas interfaceados de análise por injeção em fluxo e eletroforese capilar (FIA - CE): desafios, aplicações e perspectivas

A review about the state-of-the-art of flow injection analysis (FIA) ¾ capillary electrophoresis (CE) systems is presented. The basic principles of flow injection and capillary electrophoresis are briefly revised. The main aspects of the FIA-CE hybridization, including advantages and shortcomings, are discussed. Some applications involving all different designs are also presented. This review covers the literature from 1997 up to 2000.

Multicomutação e amostragem binária em análise química em fluxo: determinação espectrofotométrica de ortofosfato em águas naturais

A flow system based on multicommutation and binary sampling process was developed to implement the sample zone trapping technique in order to increase the spectrophotometric analytical range and to improve sensitivity. The flow network was designed with active devices in order to provide facilities to determine sequentialy analyte with a wide concentration range, employing a single pumping channel to propel sample and reagents solutions. The procedure was employed to determine ortophosphate ions in water samples of river and waste. Profitable features such as an analytical throughput of 60 samples determination per hour, relative standard deviation (r.s.d.) of 2% (n = 6) for a typical sample with concentration of 2.78 mg/L were achieved. By applying the paired t-test no significant difference at 95% confidence level was observed between the results obtained with the proposed system and those of the usual flow injection system.

An Alternative Sample Introduction Device for a Home‐Made Capillary Electrophoresis System

Abstract A home‐made capillary electrophoresis (CE) system with an alternative interface for hydrodynamic injection of sample solutions is described. The interface is an acrylic chamber whose efficiency of injection was evaluated by the separation of cysteine and methionine standards. Important parameters inherent to this system such as peristaltic pump rotation, system grounding, and injection time were carefully investigated. Although this is a batch‐wise system, the interface showed a good efficiency for nano‐liter injections and relative standard deviations (RSD) smaller than 3% for both signal measurement and migration time were obtained. This new interface allowed a minimal capillary handling and also guaranteed an excellent performance in terms of sample solution injection into the home‐made system.

Spectrophotometric determination of phosphorus in iron alloys employing a flow injection system

Um sistema de analises por injecao em fluxo e proposto para a determinacao espectrofotometrica de fosforo em ferro eletrolitico e ferro ligas. O metodo se baseia na reacao com molibdato de amonio apos reducao com cloreto estanoso em meio acido. Uma coluna com resina cationica AG50W-X8A foi acoplada ao sistema para minimizar a interferencia causada por Fe(III) e Cr(III). O sistema proposto apresentou uma frequencia analitica de 40 determinacoes por hora para uma faixa de concentracao de P de 0,25 a 6,00 mg L-1 e um baixo consumo de reagentes, 25 mg de molibdato de amonio e 2 mg de cloreto estanoso por determinacao. O desvio padrao relativo obtido para uma amostra contendo 2,20 mg L-1 P foi inferior a 1 % (n=10). Tres diferentes tipos de amostras foram empregados para avaliar o desempenho do sistema e a exatidao do procedimento proposto foi avaliada comparando-se os resultados obtidos com os valores dos materiais certificados, nao sendo observadas diferencas significativas em nivel de confianca de 95%.

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).