Flow Injection Electrothermal Atomic Absorption Research Articles

Determining Cr(III) and Cr(VI) in urine using a flow injection on-line sorption separation system coupled with electrothermal atomic absorption spectrometry and a UV/nano-Au/TiO 2 photocatalysis reduction device

In this study, an on-line nano-Au/TiO 2 photocatalysis reduction device coupled with flow injection electrothermal atomic absorption spectrometry was developed for chromium speciation in urine samples. The nano-Au/TiO 2 photocatalysis reduction device comprised a UV lamp and a Tygon tube coated with nanocrystalline Au/TiO 2 films. The process of chromium speciation in urine was based on the adsorption of Cr(III) and Cr(VI) on this photocatalysis reduction device. The absorbed Cr(VI) was photoreduced to Cr(III), and Cr(III) was eluted using 1 M formic acid. Suitable conditions for adsorption, photoreduction, elution, and subsequent ETAAS determination of the levels of Cr(III) and Cr(VI) were established. The detection limits for Cr(III) and Cr(VI) using this analytical method were 0.08 and 0.13 ng mL −1, respectively. This intra- and inter-assay precisions (relative standard deviation) for the analyses of 1 μg L −1 Cr(III) and 3.0 μg L −1 Cr(VI) were less than 10%. When urine samples were spiked at levels of 1 μg L −1 Cr(III) and 2 μg L −1 Cr(VI), the analyzed recoveries were 98.3–96.0%, respectively ( n = 3). We applied this method to the determination of Cr(III) and Cr(VI) in urine samples of human volunteers before and after supplementing their diet with chromium picolinate.

Determination of rhodium and platinum by electrothermal atomic absorption spectrometry after preconcentration with a chelating resin

The present publication describes a separation/preconcentration procedure for the subsequent trace analysis of rhodium and platinum in environmental samples. A chelating ion-exchange resin was employed for this purpose and an automatic on-line flow injection electrothermal atomic absorption spectrometry (FI-ET-AAS) method was used for the determination of trace amounts of Rh and Pt in different materials. The solutions are simultaneously treated and the ions determined sequentially. Detection limits of rhodium and platinum are 0.8 and 1.0 ng mL-1, respectively. Linearity was obtained in the range 0-50 ng mL-1 for rhodium and 0-100 ng mL-1 for platinum. The relative standard deviations were 1.8% for 10 ng mL-1 of Rh and 1.6% for 10 ng mL-1 of Pt. Enrichment factors were 20 for Rh and 14 for Pt.

An ion-exchange method for speciation of antimony by flow injection electrothermal atomic absorption spectrometry

In this work, a simple preconcentration system, achieved by replacing the sample tip of the autosampler arm by a micro-column packed with Amberlite IRA-910 or silica gel chelating resin functionalised with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel), is developed for the determination of Sb(V) and total antimony, respectively. Different factors including pH of sample solution, ionic strength, concentration and volume of eluent, sample flow rate, sample loading time and matrix effects for preconcentration were investigated. The method has been applied to the determination of antimony species in different samples.

Use of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel for automated preconcentration and selective determination of antimony(III) by flow-injection electrothermal atomic absorption spectrometry

Selective sorption of Sb(III) on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel) has been used for determination of Sb(III). A flow-injection system comprising a microcolumn connected to the tip of the autosampler was used for preconcentration. The sorbed antimony was eluted with nitric acid directly into the graphite furnace and determined by AAS. The detection limit for antimony under the optimum conditions was 0.3 ng mL(-1). This procedure was used for determination of antimony in natural water, soil, vegetation, and a certified sample of a city waste incineration ash (BCR 176).

On-line microdialysis sampling coupled with flow injection electrothermal atomic absorption spectrometry for in vivo monitoring of extracellular manganese in brains of living rats

An on-line microdialysis sampling coupled with flow injection (FI) electrothermal atomic absorption spectrometry (ETAAS) method has been developed for in vivo monitoring of extracellular diffusible Mn in brains of living rats. Microdialysates perfused through implanted microdialysis probes were collected with a sample loop of an on-line injection valve and directly introduced into the atomizer of the ETAAS by a FI system. Ultrapure saline solution (0.9% NaCl) was used as the perfusion solution at a flow rate of 1 µl min−1 through the microdialysis probe. The 25 µl of chemical modifier [0.4 g l−1 of Mg(NO3)2] and 25 µl of microdialysate were on-line mixed at a micro-Tee and loaded into a sample loop. A six-port on-line injection valve equipped with a 50 µl of sample loop, a peristaltic pump and an autosampler arm of ETAAS for direct introduction of the sample into the graphite tube were employed to act as a homemade FI system. The optimized conditions of ETAAS were performed for measurement of Mn in microdialysate. The performance characteristics of the on-line microdialysis-FI-ETAAS system for Mn were as follows: linearity range, 0–20 ng ml−1; detection limit (3σ, n = 7), 0.43 ng ml−1; recovery (n = 3), 98%–114%; precision (RSD, n = 20), 7.2%. The accuracy of the proposed on-line method was checked by four spiked artificial cerebrospinal fluid samples and compared with conventional ETAAS. The use of an on-line microdialysis-FI-ETAAS system permitted the in situ, dynamic and continuous in vivo monitoring of extracellular diffusible Mn in brains of living anaesthetized rats after administrated with MnCl2 with a temporal resolution of 25 min.

Automatic determination of iron in geothermal fluids containing high dissolved sulfur-compounds using flow injection electrothermal atomic absorption spectrometry with an on-line microwave radiation precipitation–dissolution system

A flow injection sample introduction in electrothermal atomic absorption spectrometry was used to determine iron in geothermal fluids containing high concentration of dissolved sulfate and sulfide anions. First, sulfide was precipitated as sulfur with a confluencing solution of hydrogen peroxide (10% v/v) on the walls of a knotted reactor exposed to microwave radiation, to ease the precipitation process. While the sulfate containing solution flows downstream and sequestered in a sampling arm for the sequential deposition of aliquots of sample on the graphite tube atomizer platform by means of positive air displacement, sulfur was dissolved with CCl 4 and diverted to waste. This sequence was timed to synchronize with the spectrometer computer, which had been pre-programmed to introduce aliquots of Lu modifier, previous to each sample deposition, in order to minimize the sulfate interference, to improve integrated absorbance signal and the reproducibility of measurements. By using the less sensitive iron line at 296.7 nm, the linear range was from 12 to 280 μg l −1, with a characteristic slope of 0.00083, a characteristic mass of 104.8 pg and a detection limit of 72 pg (3.6 μg l −1). The precision of the method, obtained for 10 measurements, was studied as within-run and within-batch precision; the relative standard deviations obtained in both cases were less than 3%. The accuracy of geothermal fluids has been checked by recovery tests and comparison with an independent analytical method. Results obtained by the here proposed method correlate closely with those obtained by a tedious photometric procedure with o-phenanthroline. The sensitivity and the simplicity of this on-line procedure makes it attractive for routine determination of iron in waters involving large throughput of samples.

Elimination of hydrofluoric acid interference in the determination of antimony by the hydride generation technique

For the determination of antimony by hydride generation techniques a pretreatment procedure has been developed for the reduction of Sb(V) to Sb(III) in order to remove the effect of hydrofluoric acid which strongly interferes with the reduction of pentavalent antimony to the trivalent state. It is based on the combined action of l-cysteine and boric acid at 80°C. The pretreatment is effective in both nitric and hydrochloric acid media. Quantitative recoveries are obtained in less than 60 min. Under these conditions antimony is reduced to the trivalent state in acid media containing both nitric and hydrochloric acid. The method has been applied to the determination of total antimony in certified reference materials of sediments after pressurized microwave digestion with HNO 3-HCl-HF. Good agreement is obtained by using both analytical techniques: continuous flow hydride generation atomic fluorescence spectrometry and flow injection electrothermal atomic absorption spectrometry with in-situ trapping of stibine in a graphite atomizer.

On-line ion exchange for the removal of sulfur anion interference on the determination of manganese in geothermal fluids by flow injection electrothermal atomic absorption spectrometry

An efficient flow injection system with an on-line anion-exchange resin column (Dowex-1) incorporated into a timebased injector is described for the removal of sulfur anion spectral interference for the determination of manganese by electrothermal atomic absorption spectrometry. The positive interference effect caused by high concentrations of sulfur ions could not be reduced by using different matrix modifiers. However, the elimination of this effect was possible by retaining the interferent species on the resin column and eluting the analyte with dilute nitric acid. The analyte plug was introduced into the graphite tube atomizer with a sampling arm assembly by means of positive displacement with air through a time-based solenoid valve. The entire system was controlled by a computer, independent of the spectrometer. This approach to the elimination of sulfur anion interference has been applied to geothermal fluids with a high content of these species. The linear range was from 0 to 15 µg l–1 and the detection limit was 0.2 µg l–1(4 pg) of manganese. The results were precise (2.8–3.2% RSD) and were in good agreement with those obtained by atomic absorption chelation–extraction, differences between mean values were <7%.

In vivo sample uptake and on-line measurements of cobalt in whole blood by microwave-assisted mineralization and flow injection electrothermal atomic absorption spectrometry

An on-line automated microwave-assisted mineralization and flow injection system was developed for the determination of cobalt in whole blood with in vivo sample uptake by electrothermal atomic absorption spectrometry. The samples were drawn and at the same time pumped directly from the vein of a patient's forearm to a timed injector, which is automatically controlled to inject the sample–nitric acid–anticoagulant mixture into the carrier stream. Volumes (20 µl) of the mineralized samples, collected in a capillary of a sampling arm assembly, were introduced by means of positive displacement with air through a time-based solenoid injector (TBSI) into the graphite tube atomizer. The spectrometer autosampler, used for the introduction of 10 µl of the chemical modifier, magnesium nitrate, and the furnace programme were re-programmed to synchronize with the operation of the flow system. The linear range was from 0 to 50 µg l–1 of cobalt, achieving a precision of 2.6 and 3.1% for 10 replicate analyses of a 5 µg l–1 cobalt standard solution and a certified sample, respectively, with a detection limit of 0.3 µg l–1. The agreement between the observed and certified values obtained from Seronorm Whole Blood Standard Reference Materials was good. The results obtained by using an in-batch procedure were found to linearly increase by 5% during the time interval between sample collection and analysis for the first hour; after this time the results for cobalt levelled off and were then in close agreement with those obtained by the on-line procedure proposed here.

Determination of lead in biological materials by microwave-assisted mineralization and flow injection electrothermal atomic absorption spectrometry

The design and operation of an on-line automated microwave-assisted mineralization and flow injection electrothermal atomic absorption spectrometric system for the determination of lead in biological materials are described. Certified reference materials were homogeneously dispersed in a 0.4% v/v Triton X-100 solution with an ultrasonic device. Mineralization of samples was accomplished with an HCl–HNO3 plug downstream in a PTFE coil located inside the microwave oven. A gas diffusion cell device allowed efficient degasification of mineralized samples. Precise volumes of the mineralized samples, collected in a capillary of a sampling arm assembly, were introduced by means of positive displacement with air through a time-based solenoid injector into the graphite furnace. The entire system was controlled by a computer, independent of the spectrometer. The spectrometer autosampler used for the introduction of the chemical modifier was pre-programmed to synchronize with the operation of the flow system. The linear range was from 0 to 70 µg l–1 of lead and the detection limit was 0.1 µg l–1(0.8 pg). The agreement between observed and certified values was good, except for the botanical samples Olive Leaves and Pine Needles (with an average recovery of about 90%). The main advantage of the method is that in this totally closed system with on-line sample mineralization low and repeatable blanks were obtained, allowing the rapid determination (about ten samples per hour) of lead in various biological matrices with minimum exposure to the environment and minimum operator attention.