Ana Paula Packer

Automated flow analysis system based on multicommutation for Cd, Ni and Pb on-line pre-concentration in a cationic exchange resin with determination by inductively coupled plasma atomic emission spectrometry

Abstract A flow system for on-line pre-concentration of Cd, Ni and Pb and determination by inductively coupled plasma atomic emission spectrometry is presented. The manifold comprised a set of three-way solenoid valves, which were controlled by a microcomputer running software written in Quick Basic 4.5 by means of an A/D board. Since the flow network was based on the multicommutation concept pre-concentration and elution steps could be simultaneously performed in several columns in parallel with significant analytical throughput improvement. Comparing obtained results with certified values, no significant difference at 95% confidence level was observed. Other valuable features such as an analytical throughput of 90 determinations per hour, relative standard deviation

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.

Flow system based on a binary sampling process for automatic dilutions prior to flame atomic spectrometry

Abstract A microcomputer-controlled flow system to perform automatic dilutions exploiting a binary sampling process is proposed. Introduction of precise volumes of sample and solvent was achieved by solenoid valves. The possibility to get different volumetric fractions was realized by software, which defined the time delays of the valves and could be used, e.g., for samples with analyte concentrations exceeding the analytical range. A noteworthy feature is that sample and standards processing is not necessarily the same. The analytical performance was exhaustively investigated, in particular the precision of standard measurements generated after application of different dilutions, or repeatability of results of 20 and 40 times diluted real sample solutions. The feasibility of the approach was demonstrated by the on-line automatic dilution of plant digests for determining Ca and K by flame atomic absorption and emission spectrometry. Precision of measurements performed on a solution produced by the automatic 10-fold dilution of a 100 mg l solution was characterized by a R.S.D.

Analysis of undigested honey samples by isotope dilution inductively coupled plasma mass spectrometry with direct injection nebulization (ID-ICP-MS)

Abstract Undigested honey samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) using direct injection nebulization (DIN). Samples were diluted 25-fold using dilute HNO 3 to which Triton X-100 was added. Isotope dilution (ID) was used to quantify Ba, Cu, Pb and Zn in these natural matrix samples. DIN parameters were optimized to obtain a stable transient signal enough to determine multiple isotope ratios. The Ba, Cu and Zn isotope ratios were measured in a single sample injection of 50 μl diluted honey and the Pb isotopes in a separate injection. The analysis was characterized by precisions given by R.S.D. values from 0.20 to 1.24% for Ba, 0.49–1.23% for Cu, 0.61–2.28% for Pb and 0.50–1.51% for Zn. The results were in agreement, at the 95% confidence level, with those obtained by analyzing digested samples using external calibration. Using this direct method, 30 real honey samples per hour could be analyzed.

Online isotope dilution and inductively coupled plasma mass spectrometry: from elemental to species quantification

Flow analysis has been utilized for elemental and species quantification by online isotope dilution inductively coupled plasma mass spectrometry (ICP-MS). Online isotope dilution (ID) herein refers to strategies promoting the addition of enriched isotopic solutions to the samples while flowing towards the plasma. Applications of online IDs are commonly performed in aqueous media, however, in some processes the analyte transference to the vapor phase using electrothermal vaporization, vapor generation or laser ablation is also required. Flow diagrams to perform online pre or post-column spiking with the enriched isotope for quantification by ID in speciation analysis by liquid chromatography, gas chromatography or capillary electrophoresis devices coupled to ICP-MS are presented. The main figures of merit and equations applied to elemental and species quantification by ID in flowing schemes are assessed.

Real-time simplex optimization of flow-injection systems for chemical analysis

A computer controlled flow-injection system was assembled to implement the real-time simplex algorithm. Two experimental variables. the flow rate and the sample-to-reagent ratio were controlled by a fully automated manifold. A computer interface was programmed to command the pumping speed, the introduction of sample-to-reagent amounts by solenoid valves, the on-time data acquisition and examination of the detector responses for application of the simplex algorithm. The feasibility of the approach was assessed by optimizing the flow parameters for chloride determination in water samples presenting different analyte concentrations. Optimum experimental conditions for chloride concentrations of 5.00, 25.0, 50.0 and 100 mg 1 1 were maintained. A precision characterized by rsd lower than 1% and a sample throughput of 120 h -1 were attained.