Stabilized Temperature Platform Furnace Research Articles

Optimization and validation of a methodology to determine total arsenic, As(III) and As(V), in water samples, through graphite furnace atomic absorption spectrometry

The Graphite furnace atomic absorption spectrometry (GF AAS) was the technique chosen by the inorganic contamination laboratory (INCQ/ FIOCRUZ) to be validated and applied in routine analysis for arsenic detection and quantification. The selectivity, linearity, sensibility, detection, and quantification limits besides accuracy and precision parameters were studied and optimized under Stabilized Temperature Platform Furnace (STPF) conditions. The limit of detection obtained was 0.13 µg.L-1 and the limit of quantification was 1.04 µg.L-1, with an average precision, for total arsenic, less than 15% and an accuracy of 96%. To quantify the chemical species As(III) and As(V), an ion-exchange resin (Dowex 1X8, Cl- form) was used and the physical-chemical parameters were optimized resulting in a recuperation of 98% of As(III) and of 90% of As(V). The method was applied to groundwater, mineral water, and hemodialysis purified water samples. All results obtained were lower than the maximum limit values established by the legal Brazilian regulations, in effect, 50, 10, and 5 µg.L-1 para As total, As(III) e As(V), respectively. All results were statistically evaluated.

Handling complex effects in slurry-sampling-electrothermal atomic absorption spectrometry by multivariate calibration

Analysis of solid samples by slurry-sampling-electrothermal atomic absorption spectrometry (SS-ETAAS) can imply spectral and chemical interferences caused by the large amount of concomitants introduced into the graphite furnace. Sometimes they cannot be solved using stabilized temperature platform furnace (STPF) conditions or typical approaches (previous sample ashing, use of chemical modifiers, etc.), which are time consuming and quite expensive. A new approach to handle interferences using multivariate calibrations (partial least squares, PLS, and artificial neural networks, ANN) is presented and exemplified with a real problem consisting on determining Sb in several solid matrices (soils, sediments and coal fly ash) as slurries by ETAAS. Experimental designs were implemented at different levels of Sb to develop the calibration matrix and assess which concomitants (seven ions were considered) modified the atomic signal mostly. They were Na + and Ca 2+ and they induced simultaneous displacement, depletion (enhancement) and broadening of the atomic peak. Here it is shown that these complex effects can be handled in a reliable, fast and cost-effective way to predict the concentration of Sb in slurry samples of several solid matrices. The method was validated predicting the concentrations of five certified reference materials (CRMs) and studying its robustness to current ETAAS problems. It is also shown that linear PLS can handle eventual non-linearities and that its results are comparable to more complex (non-linear) models, as those from ANNs.

Determination of indium in high purity antimony by electrothermal atomic absorption spectrometry (ETAAS) using boric acid as a modifier

The use of boric acid as a modifier for the determination of trace amount of indium in high purity antimony by electrothermal atomic absorption is described. It was found that the negative influence of the hydrofluoric acid, used for the digestion could not be eliminated by using stabilized temperature platform furnace (STPF) alone. Due to the high dissociation energy ( D 0 = 506 kJ mol −1) of indium fluoride, it is difficult to dissociate in the gas phase and hence is lost. In presence of HF (used for the dissolution of antimony), the universal Pd–Mg modifier does not work satisfactorily. Additionally, rising corrosion and reduced tube lifetime were observed when the acid digested (HF-HNO 3) antimony solution was injected in to the platform. Improvement in platform life and elimination of interferences were achieved by the addition of boric acid as a chemical modifier together with ruthenium coating of the platform. Corrosive changes of the transversely heated graphite atomizer (THGA) platform surface were examined by scanning electron microscopy. The standard addition method was applied. A characteristic mass of 36 pg was obtained. The detection limit of the proposed method is around 0.04 μg g −1. The developed method was applied to the determination of indium in real samples. The data obtained by this method were in good agreement with those obtained by ICP-MS.

Determination of Trace Amounts of Pb, Mn and Co in Acidic Solution of Vanadium, Niobium and Hafnium by Graphite Furnace Atomic Absorption Spectrometry

Graphite furnace atomic absorption spectrometry (GF-AAS) using direct atomization of the acidic sample solution was studied to establish a rapid and sensitive determination procedure of trace impurities (Pb, in and Co) in high-purity vanadium, niobium and hafnium. The interferences of matrix elements were minimized by using the stabilized temperature platform furnace (STPF) method and thereby the sensitivity of GF-AAS in trace impurities determination was significantly improved. When the weighed amount of the sample was 1 g, the limits of detection (ppm) given by 3σ of blank values were as follows: vanadium (Pb 0.12, in 0.02 and Co 0.07), niobium (Pb 0.06, in 0.02 and Co 0.07), and hafnium (Pb 0.06, in 0.02 and Co 0.06). The proposed procedure does not need the complicated pretreatment of the matrix elements such as ion-exchange separation or solvent extraction.

Improved performance of transverse heated graphite atomizers by elimination of convective gas flows

The effect of contact cylinder modification on the performance characteristics of the transverse heated graphite atomizer (THGA) was investigated with respect to sensitivity and susceptibility to interference effects in the presence of sulfates, chlorides or a silver matrix. Up to 90% improvement in sensitivity was attained by modifying the THGA housing design, especially for the determination of volatile elements with end-capped tubes. Modification of the contact cylinder did not significantly change the susceptibility to interference effects from the various matrices investigated. Normally, a lower range for the between-element recoveries was observed with an optimized contact cylinder when stabilized temperature platform furnace (STPF) conditions were used. The extent of convective gas flows in the THGA was quantified for different atomization temperatures using standard and end-capped THGA tubes with standard contact cylinders. The magnitude of the convective flow rate was estimated to be 12.2 and 14.9 ml min −1 at 900°C, and 1.4 and 1.5 ml min −1 at 2000°C for open and end-capped THGA tubes, respectively.

Serum selenium concentration of a healthy northwest Spanish population.

Selenium (Se) is an essential element, cofactor for glutathione peroxidase (GSHPx) activity, whose deficiency may induce modifications in the cellular antioxidative status and induce the appearance of different diseases. Current views suggest that a serum Se concentration inferior to 45 micrograms/L may correlate with an increased risk of coronary hearth diseases, coronary atherosclerosis and cancer. Since the Se concentration in human blood varies between geographical areas, we initiated a study to evaluate the Se status in the general healthy population of Barcelona. Serum Se concentration was investigated in a random sample of 150 subjects (age range 18-70 yr) by graphite furnace atomic spectrometry (FLAAS). L'vov platform, Zeeman background correction, and other specifications of stabilized temperature platform furnace (STPF) concept were followed. The results show that in the general population of Barcelona, Se serum concentration ranges between 60 and 106 micrograms/L (X = 80.7 +/- 10 micrograms/L). These values can be considered within the safe limits, since no subject was found with a concentration lower than the threshold of 45 micrograms/L.

Newton Method of Successive Approximations for the Linearization of the Calibration Curves of Chromium, Copper, Lead, Manganese, Silver, and Thallium in Zeeman Graphite Furnace Atomic Absorption Spectrometry

A new approach for the linearization of calibration curves in graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction was tested experimentally in an intermediate concentration region before rollover. The computational procedure employed the Newton method of successive approximations and was based on the theoretical model of L'vov et al. The calculations were based on three measured parameters: the rollover absorbance, Ar; the sensitivity ratio at the rollover point, R′; and the original background-corrected peak absorbances Az. This computational procedure generated corrected normalized integrated absorbance values A0,n with the slope identical to the slope of the original linear part of the calibration curve. The new computational procedure was employed for the linearization of calibration curves of chromium, copper, lead, manganese, silver, and thallium in Zeeman GFAAS under stabilized temperature platform furnace (STPF) conditions. Overall, the new computational procedure was able to extend the linear range of the calibration curves by a factor of 2–3 for the tested elements.

Silver and lanthanum as effective modifiers in trace determination of cadmium in nickel-base alloys by electrothermal atomic absorption spectrometry

Trace cadmium in nickel-base superalloys was determined by a stabilized temperature platform furnace using atomic absorption spectrometry with a deuterium arc background correction system. The volatility of cadmium limits the pyrolysis temperature. This prevents the removal of the interfering alloy matrix at the thermal pretreatment step. Hence, an enormously high background signal has been observed. Chemical modifiers including ammonium citrate, 1-(2-pyridylazo)-naphthol, 4-(2pyridylazo)resorcinol, 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol, Triton-X 100, EDTA, potassium nitrate, palladium nitrate, magnesium nitrate, aluminum chloride, ammonium dihydrogen phosphate, lanthanum oxide, lanthanum chloride and silver nitrate have been studied. Matrix interferences were effectively reduced by silver and lanthanum. The 100–300°C increase in the pyrolysis temperature effectively reduced the non-specific absorption from the alloy matrix. Interferences from foreign ions were also investigated. The merit of the proposed method was increased by the excellent agreement between the certified and the experimental values of Cd in the standard reference material, IN100, and the recovery obtained (100–104%). The precision of six successive replicate measurements was 4.9% with Ag modifier and 2.5% with La modifier, respectively. The results of analysing Tracealloy B were also satisfactory.

Design, operation and analytical characteristics of the filter furnace, a new atomizer for electrothermal atomic absorption spectrometry

The design of a filter furnace (FF), a new atomizer for electrothermal atomic absorption spectrometry (ETAAS) introduced earlier, has been optimized for applications in conventional analytical instrumentation. The factors controlling the analytical characteristics of the FF, i.e. the general geometry of the FF, the configuration of the dosing hole, pyrocoating, the spatial distribution of the shield gas around the FF, the amount of thread, and the porosity of the filter graphite are examined. The analytical characteristics of the improved design of the FF have been investigated and compared with those of tube and platform furnaces. The determination of high- and medium-volatility elements is evaluated in the presence of an excess of volatile matrix. The new FF has a number of advantages: the potential to set the sampling volume in the range 10–100 μl while maintaining short drying times for any volume; sensitivity levels comparable with those attainable by the stabilized temperature platform furnace (STPF) technique, without the use of matrix modifier; and significant reductions in background and chemical interference. The speed and accuracy of the method is shown in the determination of various elements in the presence of halides, seawater, nitric acid, whole blood and other chemicals. The main disadvantage of the method is that the FF components are destroyed at the temperatures required for the determination of low-volatility and carbide-forming elements.

Direct determination of zinc in seawater by graphite furnace atomic absorption spectrometry

Zinc in seawater was determined directly by graphite furnace atomic absorption spectrometry (GFAAS), using a stabilized temperature platform furnace (STPF) technique, and Zeeman background correction. Zinc in seawater was determined directly without modifier; the detection limit was 0.11 μg/1. Unpolluted seawater can be analyzed by this simple method generating results with high accuracy and precision. Significantly improved sensitivity and precision of the atomic signal were achieved when zinc in seawater was atomized from a graphite surface pretreated with vanadium (NH 4VO 3). With vanadium as modifier, the detection limit is decreased to 0.024 μg/l. The method of standard additions was used. The accuracy and precision of the developed methods were confirmed by analysis of certified reference saline waters.

Determination of Trace Amounts of Selenium in Ni-Base Heat-Resisting Alloys by Graphite Furnace Atomic Absorption Spectrometry

Graphite furnace atomic absorption spectrometry (GF-AAS) using direct atomization of the acidic sample solution was studied to establish a rapid and sensitive determination procedure of trace selenium in nickel-base heat-resisting alloys. The interferences of matrix and co-existing elements were minimized by using the stabilized temperature platform furnace (STPF) method in combination with alternating current Zeeman background correction, and thereby the sensitivity of GF-AAS in selenium determination was significantly improved. The detection limit (3σ of blank value) was 23.5 pg, which corresponded to 0.12 ppm selenium when the weight of sample was 0.5 g. The proposed procedure can be applied to the determination of selenium in nickel-base alloys without pretreatment of the sample solution and also calibration with solid standard samples or by standard additions.

Determination of arsenic, cadmium and lead in porcine and bovine kidneys by electrothermal atomic absorption spectrometry.

This paper describes an ETAAS method to quantify residues of arsenic, cadmium and lead in porcine and bovine kidneys. The results of a survey conducted during 1993 are tabulated. Analysis was performed by ETAAS with a stabilized-temperature platform furnace. The determinations were performed in the linear ranges 0.5-150, 0.04-2.0 and 1.1-75 micrograms l-1 for As, Cd and Pb, respectively, in the acid digests which were obtained under controlled conditions of temperature in a tetrafluoroethylene apparatus after appropriate dilution and addition of a suitable chemical modifier. Extensive quality assurance of the methods was performed by the standard additions method and by comparison with a certified reference material. The precision was better than 9.9, 8.5 and 9.2% for As, Cd and Pb, respectively. Low relative standard deviations of 7.4, 7.0, and 2.8% for As, Cd and Pb, respectively, were obtained by comparing the levels found in the kidney reference material and the certified values, showing this method to be satisfactory and suitable for routine analysis. The mean levels of As, Cd and Pb in porcine kidney were 2.11 (1.11-5.49), 0.81 (0.02-4.22) and 0.18 (0.02-0.42) microgram g-1 respectively. Those in the adult bovine kidney were 1.77 (0.42-3.42), 1.26 (0.01-6.16) and 0.73 (0.19-2.55) microgram g-1, respectively, and in the young bovine kidney they were 1.33 (0.61-2.56), 0.49 (0.15-1.82) and 0.20 (0.12-0.29) microgram g-1.

Critical review of the atomic spectrometric analysis of arsenic in foods

The literature on the determination of arsenic in foods by atomic spectroscopy involving hydride generation, platform furnace Zeeman and inductively coupled plasma has been critically reviewed. Hydride generation has been largely displaced as a powerful tool by platform furnace Zeeman, using the STPF (stabilized temperature platform furnace) concept for the control of interferences. Inductively coupled plasma with conventional pneumatic nebulization has been little used. An alternative is to employ hydride generation-ICP with extraction of the arsenic in an organic phase. This technique permits proper control of interferences together with an increase in sensitivity. Depending on the contents present in the foodstuff and the technique available, the sample can be solubilized by either wet or dry digestion.

Some processes occuring in graphite furnaces used for electrothermal atomic absorption spectrometry in the presence of organic chemical modifiers

Under stabilized-temperature platform furnace (STPF) conditions ascorbic acid does not significantly affect the peak areas for lead and tin and increases the peak area 1.37-fold for gallium. The appearance times for all three elements increase in the presence of ascorbic acid. The thermal decomposition of a number of organic chemical modifiers in an argon atmosphere was studied by means of thermal and elemental analysis. It was shown that the ascorbic acid melt wets lead and gallium oxides better than the glucose melt. By the use of an electron microprobe it was shown that after drying and ashing at 500°C of a solution containing ascorbic acid, lead and gallium, only 7% and 14% of the corresponding metal was retained on the surface of the carbon residue. For glucose the values were 25% and 30%, respectively. It is proposed that the increase in appearance time for the analytes studied in the presence of ascorbic acid is a result of their diffusion from the carbon residue at thte atomization stage. The sensitivity enhancement in the presence of ascorbic acid, which was observed earlier for lead, tin and a number of other elements, was caused by the substantial changes in the composition of the gas phase in the electrothermal analyser under non-STPF conditions.

Determination of lanthanum by graphite furnace atomic absorption spectrometry with a tantalum platform

A simple and sensitive method has been developed for the determination of lanthanum by graphite furnace atomic absorption spectroscopy (GFAAS). The element was determined under stabilized temperature platform furnace (STPF) conditions with atomization from a tantalum platform. Under optimized furnace conditions, the use of the tantalum surface provided better analytical sensitivity than atomization from graphite. The characteristic mass and detection limit of the methods were 220 pg and 40 μg l , respectively. At higher concentrations, the precision was about 4% RSD. The tube life was greater than 250 firings. Nitric and sulphuric acids decreased tube life.

Rapid analysis with transversely heated graphite furnace atomic absorption spectroscopy

A new graphite furnace instrument using a transversely heated furnace tube with a longitudinal Zeeman correction system has been specifically designed to provide more nearly stabilized temperature platform furnace (STPF) conditions than previous furnace systems. Because there are no cold ends on this furnace tube on which to condense analyte and matrix materials, the vapor phase interferences are expected to be smaller. Also, the cooldown step can be avoided, thus saving time. This instrument permits the delivery of sample into a furnace already heated. The delivery rate of the autosampler can be slowed. These opportunities make it feasible for the sample to be dry on the platform by the time the delivery is complete. Several elements of environmental significance were chosen for test: As, Pb, Se, Tl, Cd, Cu, Cr and V. In almost all of these situations, the analyte was fully recovered without using a matrix modifier or a pyrolysis step. However, As and Pb in urine and As in sediment required a modifier and pyrolysis step for accurate results. A new fast furnace protocol was developed to accommodate use of a matrix modifier and this new protocol was successful for Pb and As in these matrices. All the procedures required less than 1 min total cycle times and produced results in agreement with certified values. This is in contrast with conventional methods which require 2–3 min per firing. These results confirm that graphite furnace methods can be accomplished with a throughput greater than 60 determinations per hour, and eventually, it may be possible to increase this rate beyond 100 determinations per hour.

Determination of copper, iron, aluminium, lead and cadmium in cork stoppers by electrothermal atomic absorption spectrometry

Methods for the determination of five elements (Cu, Fe, Al, Pb and Cd) in cork stoppers by electrothermal atomic absorption spectrometry (ETAAS) with a stabilized temperature platform furnace are described. A previous acid digestion of the cork stoppers in HNO3–HCl–HF in poly(tetrafluoroethylene) apparatus, was required owing to the specific and characteristic nature of cork. The digests were evaporated to dryness and the residue was dissolved in HNO3 for subsequent measurement by ETAAS. Depending on the metal, a suitable chemical modifier was added when necessary, i.e., Mg(NO3)2 for Al and Fe, a mixture of Mg(NO3)2 and Pd(NO3)2 for Pb and NH4H2PO4 for Cd. The linear ranges for determination were 0.6–50, 0.8–50, 1.5–50, 1.1–75 and 0.4–2.0 µg l–1 for Cu, Fe, Al, Pb and Cd, respectively, after appropriate dilution. For precision and recovery studies, several determinations (from six to ten) for each of the five metals were conducted on different aliquots of the same sample, using the standard additions method at three specific concentrations. The relative standard deviations were 11.4, 9.4, 15.0, 9.5 and 7.1% for Cu, Fe, Al, Pb and Cd, respectively, which makes this method satisfactory and suitable for routine analysis.

Hydride generation flow injection using graphite furnace detection: emphasis on determination of tin

Hydride generation, (HG), using flow injection methods, (FI), provides an ideal way to separate the hydride-forming analytes from a large volume of matrix. By trapping the hydrides on a Pd-coated L'vov platform at low temperature, it can be shown that the full process is at least 80% efficient for As, Bi, Ge, Sb, Se, Sn and Te. While this work was not fully automated, the various functions were conducted on-line. This method has been tested for the determination of Sn in various samples. The Pd-treated stabilized temperature platform furnace, (STPF), was used for in situ trapping and atomization of the analyte. Integrated absorbances were used for the measurement of the analytical signal. The detection limit for Sn was 7 ng l for a 10-ml sample. The analytical precision was 3–5% RSD at 1 ng of Sn. Inter-element interferences were investigated. The method has been applied to the determination of Sn in NIST Steel, River Sediment, Orchard Leaves and Bovine Liver Standard Reference Materials.

Determination of gadolinium in biological materials using graphite furnace atomic absorption spectrometry with a tantalum boat after solvent extraction

A method was developed for the determination of gadolinium (Gd) in biological material using graphite furnace atomic absorption spectrometry (GFAAS). The element is first extracted into methyl isobutyl ketone and then reextracted into hydrochloric acid. Factors influencing the recovery of extraction such as pH, choice of chelating agents, and hydrochloric acid concentration have been investigated. The element is determined under STPF (stabilized temperature platform furnace) conditions with atomization from a tantalum boat. Under optimized furnace conditions, the use of the tantalum boat improved sensitivity substantially compared to the use of pyrolytically coated graphite tubes. Around 150 measurements could be performed with 1 boat. Memory effects, being a common problem in the GFAAS determination of lanthanoids, were no longer observed after insertion of the boat. The characteristic mass and detection limit (2SD; SD = standard deviation) of the Gd determination are 1000 and 2060 pg, respectively. The precision evaluated as the relative standard deviation (RSD) of six analyses was below 10% for tissue Gd concentrations ranging from 0.92 to 72.0 micrograms g-1. The recovery of added analyte ranged between 92.0% and 99.3%. The method was found to be suitable for studying the pharmacokinetics and biodistribution of Gd in rats.

Electrothermal Atomic Absorption Interactions among Trace and Major Elements in Environmental Samples: Determination of Cadmium in the Selective and Total Dissolution of Marine Sediments

Electrothermal Atomization Atomic Absorption Spectrometry (ETA-AAS) is one of the most popular and widely used techniques for trace element determination. Nevertheless, the chemical reactions occurring in the graphite furnace are still the subject of theoretical and experimental investigations. As a consequence, this technique cannot yet be considered to have attained a state of maturity, mainly because of the frequent occurrence of spectral and nonspectral interference effects. The degree of interference varies with the atomization system used. Slavin and co-workers have described a system called the Stabilized Temperature Platform Furnace or STPF. While many workers use parts of the system, troubles remain when the system is fragmented. The various parts of the system are interactive and some of the interactions are still inadequately understood. As will be described below, instrumental settings are not sufficient to overcome interferences.