Solid Sampling-graphite Furnace Atomic Absorption Research Articles

Direct analysis of silica by means of solid sampling graphite furnace atomic absorption spectrometry

This paper reports on the use of solid sampling-graphite furnace atomic absorption spectrometry for the direct analysis of synthetic amorphous silica. In particular, determination of hazardous elements such As, Cd, Cr, Cu, Pb and Sb is investigated, as required by regulations of the food industry.The conclusion of the work is that, after proper optimization of the working conditions, paying particular attention to the atomization temperature and the use of proper modifiers (graphite powder, HNO3 or Pd), it is possible to develop suitable procedures that rely on the use of aqueous standard solutions to construct the calibration curves for all the elements investigated. The proposed method shows important benefits for the cost-effective analysis of such difficult samples in routine labs, permitting fast screening of those elements that are very rarely present in this type of sample, but also accurate quantification of those often found, while offering low limits of detection (always below 0.1mgg−1) that comply well with legal requirements, and precision levels that are fit for the purpose (approx. 6–9% R.S.D.).

Direct determination of Hg in polymers by solid sampling-graphite furnace atomic absorption spectrometry: A comparison of the performance of line source and continuum source instrumentation

This work explores the potential of solid sampling-graphite furnace atomic absorption spectrometry (SS-GFAAS) for the fast and direct determination of Hg in polymers. Eight certified reference materials with different composition (polyethylene-PE-, polystyrene-PS-, poly vinyl chloride-PVC- and acrylonitrile butadiene styrene-ABS-) were selected for the study, covering a wide Hg content range (from 20 to 1100 μg g − 1 ). The difficulties found in achieving a selective atomization of the analyte from these samples were partially mitigated by the maintenance of the Ar flow during the atomization step, leading to an improved signal-to-background ratio. Even then, when a line source (LS) GFAAS instrument was employed for analysis, it was only possible to develop truly accurate procedures relying on the use of aqueous standards for calibration for PE and PVC samples, and different atomization conditions (1200 °C and 1300 °C, respectively) were needed for the two types of samples. The use of high-resolution continuum source (HR-CS) GFAAS instrumentation permitted to improve this situation significantly thanks to its higher potential for the correction of high and fast changing background. With such an instrument, satisfactory results could be obtained for all the samples under study using the same atomization conditions (1200 °C) and aqueous standard solutions for calibration. Additionally, the HR-CS GFAAS technique presented a lower limit of detection (0.6 μg g − 1 for CS and 2.2 μg g − 1 for LS), a broader linear range (10 to 320 Hg ng for CS, and 20 to 200 ng for LS), and a somewhat improved sensitivity (approximately 0.0030 s ng − 1 for CS using the three central pixels for quantification, and approximately 0.0025 s ng − 1 for LS). Overall, the use of HR-CS GFAAS permits obtaining significant advantages for the determination of this complex analyte in plastics, such as straightforward calibration with aqueous standards, a high sample throughput (15 min per sample), sufficient precision (4–9% RSD), a suitable limit of detection, and reduced risk of analyte loss and contamination.

Minimally-invasive filter paper test in combination with solid sampling-graphite furnace atomic absorption spectrometry for Pb determination in whole blood

This work describes a simple procedure for the determination of blood lead levels in dried-spot filter paper specimens. The method permits the minimally-invasive collection of blood on filter paper and the subsequent direct analysis of discs punched from these filters by solid sampling-graphite furnace atomic absorption spectrometry (SS-GFAAS). A systematic study on the possible effects of different factors (total volume of blood deposited onto the filter paper, potential chromatographic effects affecting the distribution of Pb over the surface, potential differences in the amount of blood deposited per surface area for samples with different hematocrit values) was carried out, leading to the conclusion that the variation of these parameters within the usual clinical range does not result in any significant effect on the amount of Pb deposited in each disc. Thus, a simple methodology was developed based on (i) the performance of Pt as a chemical modifier and (ii) the use of matrix-matched standards for calibration (Pb-free blood samples spiked with known amounts of Pb) treated in the same way as the samples. The method was validated by analysis of a reference material, as well as by comparison of the results obtained for 18 patients from which blood was also taken and analyzed following the standard procedure (venous sampling, blood dilution and GFAAS monitoring). The main analytical features of the method proposed are: a detection limit of 2.5 μg Pb L−1, a working range up to 840 μg Pb L−1, a sample throughput of approximately 10 min per sample (5 replicates) and precision values below 10% RSD. The ease of sample collection, transporting and storing, in combination with the expeditiousness and relative inexpensiveness of the analytical technique used, make the procedure investigated very attractive for the screening of children in order to detect those with blood lead levels above the present threshold of concern (100 μg L−1), particularly in countries/areas were collecting sites might be far away from central laboratories.

Direct determination of nickel in petroleum by solid sampling–graphite furnace atomic absorption spectrometry

A procedure for the direct GFAAS determination of Ni in petroleum samples using a solid sampling strategy is proposed. Palladium was used as conventional modifier. Central composite design multivariate optimization defined the optimum temperature program and the Pd mass, allowing calibration using aqueous analytical solution. The limit of detection (LOD) at the optimized conditions was 0.23 ng of Ni, for typical sample masses between of 0.10 and 0.60 mg. Linearity at least up to 11 ng of Ni and a characteristic mass of 45 pg were observed, defining a dynamic range between 0.52 and 110 microg g(-1). Typical coefficients of variation (n = 10) in the analysis of oil reference materials were 7%. Method validation was performed both by the analysis of oil certified reference materials and by comparison with an independent method (ASTM 5863-B). No statistically significant difference was observed between obtained and expected values. The total determination cycle lasted 5 min, equivalent to a sample throughput of 6 h(-1) for duplicate determinations.

Solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of boron in plant tissues

In this work, the potential of graphite furnace atomic absorption spectrometry for the direct determination of B in plant tissues has been investigated. Three certified reference materials (NIST SRM 1570a spinach leaves, NIST SRM 1573a tomato leaves and BCR CRM 679 white cabbage) were selected for this study, the goal always being to develop a fast procedure that could be robust enough to provide a satisfactory performance for all of them, without any modifications in the conditions applied. The use of a suitable chemical modifier was found to be essential for obtaining a reproducible and sufficiently sensitive signal for boron solutions. In this regard, the performance of the combination of citric acid plus W (added as a permanent modifier) was noteworthy, resulting in well-defined signal profiles, a remarkable analyte stabilization during the pyrolysis step (up to 2100 °C) and minimal memory effects. This mixture of modifiers provided a good performance for the direct analysis of solid samples as well, but only if a suitable temperature program, favoring the interaction between the analyte and the modifiers, was used. Thus, such a temperature program, with two pyrolysis steps and the addition of NH 4NO 3 in order to carry out the in situ sample microdigestion, was optimized. Under these conditions, the peak areas obtained for both solid samples and aqueous standards were comparable. Finally, the analysis of the samples was carried out. In all cases, a good agreement with the certified values was obtained, while R.S.D. values ranged between 6 and 10%. It can be concluded that the method proposed shows significant advantages for the determination of this complicated element in solid samples such as the use of aqueous standards for calibration, a high sample throughput (20 min per sample), a suitable limit of detection (0.3 μg g −1) and reduced risk of analyte losses and contamination.

Solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of silver at trace and ultratrace levels

In this work, the possibilities of solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of silver in solid samples of very different nature (a biological sample, a soil, an ore concentrate and a polymer) and showing substantial differences in their analyte content (from approximately, 40 ng g −1 up to 350 μg g −1) have been evaluated, the goal always being to develop fast methods, only relying on the use of aqueous standards for calibration. Different factors had to be taken into account in order to develop suitable procedures for all the samples under investigation. Among the most important ones, the following can be mentioned: (i) optimization of the temperature program in order to selectively atomize the analyte; (ii) the use of chemical modifiers (such as Pd or HNO 3), depending on the sample characteristics; (iii) appropriate wavelength, argon flow and sample mass selection (depending on the analyte content); (iv) the use of 3-field mode Zeeman-effect background correction in order to further expand the linear range up to 1000 ng of Ag, which was needed for analysis of the sample showing the highest Ag content (polypropylene). The procedures finally proposed show interesting features for the determination of silver in solid samples: the advantage of using aqueous standard solutions for calibration, a high sample throughput (approximately, 15 min per sample), a low detection limit (2 ng g −1), sufficient precision (R.S.D. values in the vicinity of 10%) and a reduced risk of analyte losses and contamination.

Solid sampling-graphite furnace atomic absorption spectrometry for Hg monitoring in soils. Performance as a quantitative and as a screening method

This work explores the potential of solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of Hg in soils. Taking advantage of the high volatility of the analyte when compared with that of most matrix components, and using KMnO4 as the chemical modifier, a quantitative method was developed, allowing for the fast and reliable determination of Hg in seven different soil certified reference materials. The main features of this method are: a detection limit of 25 ng g−1, RSD values between 3 and 12% and straightforward calibration with aqueous standards. Furthermore, the paper discusses in detail how to transform this quantitative method into a screening method, intended for those situations in which only a binary response (Yes/No) is required (e.g., routine control of agricultural soils in the European Community, for which a legal limit of 1.5 μg g−1 Hg has been established). The screening method proposed permits obtaining an answer in 6–10 min per sample. For this method, a narrow region of unreliability was calculated (1.15–1.95 μg g−1), such that only the samples that fall into this region should be further analyzed by means of a more precise technique.

Solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of Au in samples of various natures

In this work, the possibilities of graphite furnace atomic absorption spectrometry for the direct determination of Au in solid samples (NIST SRM 2709 San Joaquin soil, CANMET PTC-1a Co–Ni sulfide concentrate and a vitamin complex) have been evaluated. The diverse volatilities of the matrixes resulted in different degrees of difficulty for Au determination. In this regard, the analysis of the less volatile samples (CANMET PTC-1a and NIST SRM 2709) was particularly challenging. For these materials, the addition of Na2CO3 solutions, in order to carry out a microfusion directly in the graphite furnace, was found to be essential to liberate structurally bound gold at a moderate temperature (2000–2100 °C). In all the cases investigated, accurate results were obtained by means of external calibration using aqueous standards. Every determination required ≈15–20 minutes. Precision ranged between 12 and 14% relative standard deviation. A detection limit of 15 ng g−1 was calculated.

Solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of trace amounts of silicon in polyamide. Comparison of the performance of platinum and palladium as chemical modifiers

In this paper, the use of solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of silicon in a polyamide sample at the 10 μg g −1 level has been investigated. The performance of Pt and Pd as chemical modifiers for the reproducible atomization of this element has been compared, both for aqueous solutions and for solid samples. According to the results obtained, it can be concluded that Pt is an interesting alternative to Pd, since it is capable of providing a similar performance with the use of lower modifier amounts (1 μg of Pt vs. 20 μg of Pd for direct analysis of the sample). The method proposed shows important benefits for the determination of such a complicated element: the use of aqueous standards for calibration, low sample consumption (a few milligrams), high sample throughput (20 min per sample), low limit of detection (0.1 μg g −1) and reduced risk of analyte losses and, especially, of contamination, while precision is fit for the purpose (approx. 6% R.S.D.).

Evaluation of solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry and solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of Cr in various materials using solution-based calibration approaches

In this work, the possibilities for the direct determination of Cr in solid samples by means of graphite furnace atomic absorption spectrometry (SS-GFAAS) and by means of electrothermal vaporization-inductively coupled plasma mass spectrometry (SS-ETV-ICPMS) have been critically evaluated and compared, the goal always being to develop simple and fast methods, only relying on the use of aqueous standards for calibration. Four reference materials of very different nature (milk powder, lobster hepatopancreas, polyethylene and sewage sludge), covering a wide Cr concentration range (from 17.7 ng g−1 to 37.2 µg g−1), were selected for the study. The diverse volatility of their matrixes, compared with that of Cr, resulted in different degrees of difficulty for both techniques. SS-GFAAS offers a better limit of detection (2 ng g−1) than SS-ETV-ICPMS (30 ng g−1), mainly due to the occurrence of C-based polyatomic interferences with the latter technique. The samples that presented the least difficulties were those for which the matrix is mainly of an organic nature and can be easily removed during the pyrolysis step, allowing a selective atomization/vaporization of the analyte. Under these circumstances, external calibration against aqueous standards was feasible for SS-GFAAS in all cases. SS-ETV-ICPMS proved to be more sensitive to matrix effects, but the use of the palladium (added for its carrier properties) signal as internal standard also allowed the use of this straightforward calibration procedure. On the other hand, the analysis of sewage sludge (containing 85% of hardly volatile inorganic compounds) represented the most complicated situation for both techniques: for SS-GFAAS, the addition of Na2CO3 to effect an in-situ microfusion of the sample during the pyrolysis step greatly helped to improve the situation, while for SS-ETV-ICPMS the single standard addition method was necessary. In all cases, a good agreement with the certified values was obtained. The precision ranged between 6 and 22% relative standard deviation, depending on the homogeneity and the sample mass used. These values could be further improved, if needed, by increasing the number of replicates per determination (usually five). Every determination required approximately 15–20 min, except when the single standard addition method was used (30–40 min). Therefore, it can be stated that both techniques show the capability of providing a direct determination of this analyte in a variety of samples, at very different concentration levels, allowing the development of fast and reliable solid sampling procedures.

Direct determination of cobalt and zinc in samples of different volatility by means of solid sampling–graphite furnace atomic absorption spectrometry

In this work, a method has been developed for the direct determination of cobalt and zinc in two different real-life samples (a vitamin complex and an agricultural soil) by means of solid sampling–graphite furnace atomic absorption spectrometry. The selection of the elements and of the samples was based on their different volatility and complexity, the final aim being to check the maturity of solid sampling–graphite furnace atomic absorption spectrometry to deal with different situations, and to further contribute to the development of a general methodology that could be used for a large variety of cases. In order to achieve these goals a systematic study was carried out by selection of the most appropriate working conditions and optimization of the sample mass. It can be stressed that the maintenance of the Ar flow (250 ml min −1) during the atomization step was found to be especially useful to improve the signal to background ratio for those situations in which simultaneous release of the matrix and atomization of the analyte was unavoidable (Co determination in soil). Comparison of the results for both samples showed no significant differences (other than some disparity regarding the optimum mass range), proving that solid sampling–graphite furnace atomic absorption spectrometry can be as appropriate for soil analysis as it is for the analysis of organic samples, if appropriate working conditions are chosen. The method finally proposed shows interesting features for the determination of the analytes in the samples such as: the ability to use aqueous standard solutions for calibration, a high sample throughput (15–20 min analysis time per analyte in a sample), the fact that it is unnecessary to use hazardous reagents, a low sample consumption, adequate limits of detection (0.5 mg kg −1 for Co and 4.1 mg kg −1 for Zn in the soil sample), suitable precision values (R.S.D. ∼8%) and a reduced risk of analyte losses and contamination.

Solid sampling-graphite furnace atomic absorption spectrometry for palladium determination at trace and ultratrace levels

In this work, the possibilities of solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of palladium in solid samples of different origin (a polymer, a pharmaceutical drug and a used auto catalyst reference material), and showing substantial differences in their palladium content (from approximately 2 ng g−1 to 326 µg g−1), have been evaluated. The influences of different factors on the results, such as (i) the temperature program, (ii) the use of chemical modifiers, (iii) appropriate wavelength and argon flow selection (depending on the analyte content) and (iv) the sample mass, have been investigated. The method finally proposed shows interesting features for the determination of palladium in solid samples: the advantage of using aqueous standard solutions for calibration, a high sample throughput (15 min per sample), the fact that no hazardous reagents have to be used, the low detection limit (0.4 ng g−1 for enalapril maleate), sufficient precision (RSD values are between 3 and 15%, depending on the characteristics of the sample) and a reduced risk of analyte losses and contamination. Therefore, it is an attractive alternative to the time-consuming pre-concentration approaches currently in use for palladium determination at low levels.

Direct determination of copper and lead in sewage sludge by solid sampling-graphite furnace atomic absorption spectrometry — study of the interference reduction in the gaseous phase working in non-stop flow conditions

Graphite furnace atomic absorption spectrometry is most useful for the determination of metals in solid samples when samples with a slow or complicated dissolution process are used. Its application to inorganic matrixes (especially geological material), therefore, appears to be a field of great interest. However, most of the papers published to date deal with organic samples. In the present paper two different strategies for the direct determination of metals in inorganic samples are proposed depending on the relationship between the analyte atomization temperature and the vaporization temperature of the matrix. For the more complicated case where both temperatures are similar, working in non-stop flow conditions is proposed because it permits a considerable reduction of interferences in the gas phase. This way the determination of lead and copper in a sewage sludge sample was carried out. The results can be considered as satisfactory with regard to both accuracy and precision (R.S.D. of 7.8% and 5.7%, for Pb and Cu, respectively), as they are similar to previous ones obtained for mainly organic less problematic samples.

Direct determination of phosphorus in two different plastic materials (PET and PP) by solid sampling-graphite furnace atomic absorption spectrometry

P is an element that is difficult to determine accurately by most analytical techniques when present at low levels. In particular, P is an additive in many plastics and its rapid determination is of economic interest. Solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) may be an approach that combines high sample throughput with an improvement in sensitivity and it is particularly suitable for dealing with organic matrices when speed is more important than high precision. In this work, SS-GFAAS was used for the determination of P in PET (polyethyleneterephthalate) and PP (polypropylene) materials, showing the suitability of the approach for this kind of analysis. In order to enable P determination, a combination of Pd and ascorbic acid was used as a chemical modifier. The results obtained can be considered satisfactory with regard to the sensitivity (LOD 2.5 µg g−1) and precision achieved (7.8% RSD for the PET sample with a P content of about 45 µg g−1 and 6.7% RSD for the PP sample with a P content of about 1000 µg g−1), values similar to those obtained for less problematic analytes. Previous analysis of the PET material by means of solid sampling-electrothermal vaporization-ICP-MS (SS-ETV-ICP-MS) enabled us to compare the performance of both methods. Special attention was paid to the peculiar relationship between signal and sample mass that SS-GFAAS is reported to display.

The use of chemical modifiers in the determination of cadmium in sewage sludge and tin in PVC by solid sampling-graphite furnace atomic absorption spectrometry

The effects of NH 4H 2PO 4 and Pd as chemical modifiers in SS-GFAAS are studied in the determination of Cd in sewage sludge and of Sn in PVC samples. Whereas for Cd both modifiers act equally well whether Cd is in solution or in the solid sample, the effect of Pd on tin is different. To make the Pd modifier as effective on Sn in PVC as on Sn in solution a two-step pyrolysis must be introduced into the temperature programme. It is also shown that the contribution of the application of chemical modifiers to the final imprecision of the determination is negligible compared to that introduced by the sample inhomogeneity.

Screening of antimony in PVC by solid sampling-graphite furnace atomic absorption spectrometry

The development of two-stage control systems is of great interest when a large number of samples are analysed in order to check that they fulfil certain requirements. If the first stage is carried out using an inexpensive method with a high throughput which makes it possible to filter out the majority of the samples that fulfil the requirements, the procedure is not only less time-consuming but also more economical. Direct determination of metals in solid samples by graphite furnace atomic absorption spectrometry (GFAAS) appears, in principle, to be a suitable analytical technique for screening purposes since it provides sufficiently reliable results in a reasonably short time. In this paper it is applied with satisfactory results to antimony content control in a PVC sample.