Direct determination of iron in sand using solid sampling graphite furnace atomic absorption spectrometry

A fast and reliable method for the direct determination of iron in sand by solid sampling graphite furnace atomic absorption spectrometry was developed. A Zeeman-effect 3-field background corrector was used to decrease the sensitivity of spectrometer measurements. This strategy allowed working with up to 200 μg of samples, thus improving the representativity. Using samples with small particle sizes (1–50 μm) and adding 5 μg Pd as chemical modifier, it was possible to obtain suitable calibration curves with aqueous reference solutions. The pyrolysis and atomization temperatures for the optimized heating program were 1400 and 2500 °C, respectively. The characteristic mass, based on integrated absorbance, was 56 pg, and the detection limits, calculated considering the variability of 20 consecutive measurements of platform inserted without sample was 32 pg. The accuracy of the procedure was checked with the analysis of two reference materials (IPT 62 and 63). The determined concentrations were in agreement with the recommended values (95% confidence level). Five sand samples were analyzed, and a good agreement (95% confidence level) was observed using the proposed method and conventional flame atomic absorption spectrometry. The relative standard deviations were lower than 25% (n = 5). The tube and boat platform lifetimes were around 1000 and 250 heating cycles, respectively. Correspondence: Pedro V. Oliveira, Instituto de Química, Universidade de S?o Paulo, CP 26077, 05513-970 S?o Paulo, SP, Brazil     

Direct determination of atmospheric lead by Zeeman solid sampling graphite furnace atomic absorption spectrometry (GFAAS)

Summary Atmospheric lead was collected by membrane filters using two low volume air samplers at Jülich, Stolberg, and Wetzlar, Federal Republic of Germany. Sampling times varied from 2 to 8 h. After sampling, each filter was subsampled in two cross-sections using a clean stainless steel punch (diameter 5 mm). The lead content of each subsample disc was determined directly by Zeeman GFAAS, calibrated with aqueous standard solutions and supported by solid reference materials. The distribution of lead between the subsamples was generally homogeneous, with standard deviations ranging from 11 to 37%, but typically <15% for samples with 8 h sampling time. The analysis of each filter usually took about 30 min. The differences in air quality between the three sampling locations, as measured by the lead concentrations, are discussed. In general, Stolberg appears to have the highest lead concentrations. The mass particle-size distribution of lead in the aerosol samples collected by membrane filters using a cascade impactor at Stolberg was also investigated with the same analytical technique. Using graphite platform boats as direct samplers, it is possible for the dry deposition flux of lead to be estimated. This provides a quick means of assessing the levels of lead pollution in the atmospheric environment. With lead concentrations measured in parallel, the dry deposition velocities of lead can be estimated under various meteorological conditions. Application of similar sampling and analytical techniques to other atmospheric trace metals may be possible.     

Slurry sampling for graphite furnace atomic absorption spectrometry

Summary Slurry preparations are an effective way to introduce solids into the graphite furnace. Ultrasonic agitation keeps samples mixed prior to analysis. Several aspects of the ultrasonic slurry sampling approach are discussed including contamination concerns, analyte partitioning, and the effect of particle size. In addition, sample preparation strategies for slurry preparations of non-powdered materials are reviewed. The suitability of this method for assessing homogeneity is demonstrated.     

Improved algorithm for linearization of calibration curves in Zeeman graphite furnace atomic absorption spectrometry

A two-parameter model for simulation of concentration curves in Zeeman graphite furnace atomic absorption spectrometry is proposed. The algorithm based on this model can be used for linearization of calibration curves up to the roll-over point. The merits of the algorithm are supported by experimental data obtained for 20 elements under different measurement conditions (light source current and slit width), including the cases where the curvature of the initial calibration curves originates partially from mass-dependent chemical effects and/or non-uniform atom distribution over the furnace cross section. The linearization error does not exceed the random scatter for replicates.     

Direct determination of trace amounts of arsenic in powdered biological samples by atomic absorption spectrometry using an inner miniature cup for solid sampling techniques

Summary A new easy solid sampling technique with atomic absorption spectrometry by using an inner miniature cup in conjunction with the cupped type furnace was proposed for the direct determination of arsenic in NBS, NIES standard materials and marine organisms. A mixture of 3 M sulfuric and 4 M nitric acid solution containing 60 g of nickel was successfully used as the matrix modifier for the powdered samples examined. Optimum experimental conditions were determined based upon detailed examinations for the trace amount determination of arsenic in these samples. Analytical sensitivity and accuracy of this method were compared to the arsine generation followed by atomic absorption or ICP emission spectrometry. The standard deviations for 7–15 ppm As were found to be 3–10%.

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Direkte Bestimmung von Arsenspuren in pulverföraügen biologischen Proben durch AAS mit Hilfe eines im Ofen einsetzbaren Miniaturbechers für feste Proben

Zusammenfassung Zur direkten Arsenbestimmung in NBS und NIES-Referenzmaterialien sowie Meeresorganismen durch AAS wurde ein in einen entsprechenden Ofen einsetzbarer Minaturbecher verwendet. Als Matrixmodifikator wurde ein Gemisch von 3 M Schwefel- und 4 M Salpetersäure mit 60 g Ni benutzt. Die optimalen Bedingungen wurden durch detaillierte Untersuchungen gefunden. Empfindlichkeit und Genauigkeit des Verfahrens wurden mit der Methode der Arsinerzeugung mit nachfolgender AAS oder ICP-AES verglichen. Relative Standardabweichungen von 3–10% für 7–15 ppm As wurden gefunden.

     

Effectiveness of linearization of calibration curves in Zeeman graphite furnace atomic absorption spectrometry

A theoretical analysis is made of the effect of analytical line broadening and of non-absorbable radiation in the light source on the shape of concentration curves in Zeeman graphite furnace atomic absorption spectrometry. These results have been used in a systematic study of the effect of spectrometer slit width and hollow-cathode lamp (HCL) current on linearization of calibration graphs for 11 elements: Ag, Au, Bi, Cd, Co, Cu, Fe, Mn, Ni, Pb, and Sb. The effectiveness of linearization throughout the analytical range covered was estimated experimentally on series of 25–30 solutions. Three solutions in each series were used as standards for constructing the calibration graph, the others serving to evaluate the linearization effectiveness. Increasing the slit width and decreasing the HCL current compared to the standard measurement conditions have permitted us to reach a sufficiently high effectiveness of linearization for all the elements studied, with the exception of Ni. The maximum deviation of experimental points from the linear graph under optimum conditions does not exceed 6%. The effect of the Δ parameter used in the computational algorithm on linearization effectiveness is investigated.     

A collaborative study using solid sampling graphite furnace atomic absorption spectrometry

A first collaborative study was carried out to test the precision and accuracy of solid sampling graphite furnace atomic absorption spectrometry (SS-ZAAS). Seven test materials, i.e. red cabbage, two bovine liver materials, milk powder (BCR 150), kale, industry dust, and fish homogenate were sent to 11 participants. These test materials were analyzed for cadmium, lead, copper and mercury. Precision was calculated as the repeatability (r) and the reproducibility limits (R). Accuracy was calculated with respect to the Certified Reference Material BCR 150, milk powder. Results showed that the accuracy for milk powder was excellent, and that most results regarding repeatability and reproducibility limits were satisfying. However, some problems were met especially with copper in bovine liver and cadmium and copper in industry dust. It was not clear what caused the problems: the method SS-ZAAS or the inhomogeneity of the material. Especially the industry dust test material has to be studied further in order to locate the origin of the problems.Presented at the 5th International Colloqium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992, Geel, Belgium     

Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry

A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing.     

Direct flame solid sampling for atomic absorption spectrometry: determination of copper in bovine liver

In this work a new device for the direct introduction of solid samples into flame atomizers is proposed. The determination of copper in bovine liver reference material by flame atomic absorption spectrometry (FAAS) using a conventional air–acetylene flame was chosen as an example. Between 0.05 and 0.50 mg of the test sample was weighed directly into a small polyethylene vial connected to a glass chamber. A flow of air carries the test sample as a dry aerosol to a T-shaped quartz cell positioned above the burner in the optical path. The atomic vapor generated produces a transient signal of less than 3-s duration; integrated absorbance is used for signal evaluation. Optimized conditions for air flow rate, flame stoichiometry, etc., were evaluated. There was no statistical difference between the results from the proposed system, compared with those obtained by prior sample digestion and determination by conventional FAAS. No excessive grinding of the samples was required and samples with particle size less than 80 μm were used throughout. Background signals were always low and a characteristic mass of 1.5 ng was found for Cu. The proposed system allows the determination of 60 test samples in 1 h and it can be easily adapted to conventional atomic absorption spectrometers.     

Single drop microextraction combined with graphite furnace atomic absorption spectrometry for determination of lead in biological samples

Single drop microextraction combined with graphite furnace atomic absorption spectrometry is introduced for the determination of trace lead in water samples. A drop of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) dissolved in benzene was held at the tip of a microsyringe and immerged into the sample solution which was stirred, the solvent drop interacts with the sample solution, and the analyte was extracted into the drop and concentrated. After extracting for a period of time, the drop was retracted into the microsyringe and directly injected into graphite furnace for GFAAS determination of Pb. Several factors affecting the extraction efficiency, such as pH of sample solution, drop volume, stirring rate and extraction time, were optimized. Under the optimized conditions, an enhancement factor of 16 was achieved, and the detection limits for Pb were 25 ng L⁻¹. The relative standard deviation for seven replicate determination of 10 ng mL⁻¹ Pb was 6.1%. The method was applied to determine trace Pb in biological samples with satisfactory results. Correspondence: Pei Liang, Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P.R. China     

Maintenance of the slope of linearized calibration curves in Zeeman graphite furnace atomic absorption spectrometry

L'vov and co-workers developed a theoretical model and computational procedure (B.V. L'vov, L.K. Polzik and N.V. Kocharova, Spectrochim. Acta Part B, 47 (1992) 889 and B.V. L'vov, L.K. Polzik, N.V. Kocharova, Yu.A. Nemets and A.V. Novichikhin, Spectrochim. Acta Part B, 47 (1992) 1187) that linearized calibration curves in Zeeman graphite furnace atomic absorption spectrometry by taking into account the presence of stray light. The calculations of L'vov and co-workers were based on three parameters: the rollover absorbance A_r, Zeeman sensitivity ratio R, and the original background corrected peak absorbance values A_z. In order to simplify the calculations, R was assumed to be unity. In the studies reported here, this simplification is shown to be unsatisfactory because the slope obtained in the upper portion of the calibration curve, after linearization, is found to be different from the slope obtained in the normal linear region. Deviations between these slopes were found to be as high as 30%. The present work also shows that the theoretical model of L'vov and co-workers does not have a mathematical solution at high values of A_z. This failure of the model prevents its use at high A_z values. The physical nature of this failure is still unclear, which points to the necessity for further work to understand the inadequacies of the present theory. In the present studies, calculations based on the Newton method of successive approximations (A.I. Yuzefovsky, E.G. Su, R.G. Michel, W. Slavin and J.T. McCaffrey, Spectrochim. Acta Part B, 49 (1994) 1643), allow incorporation of the experimental value of R at the rollover point R′, which better linearizes the calibration curves. By use of this approach, a satisfactory result is obtained for lead (R′ = 0.67) up to the point of failure of the model at high values of A_z.     

On the direct analysis of solid samples by graphite furnace atomic absorption spectrometry

Summary We have studied some limitations of the solid sampling, cup-in-tube technique by comparison with a constant temperature two-step atomiser and found consistently lower vapour-phase temperatures and greater interferences in the former. With the former, higher vapour-phase temperatures and improved analytical results for lead and cadmium were found using Pd(NO₃)₂+Mg(NO₃)₂ instead of NH₄H₂PO₄+Mg(NO₃)₂ as modifier. Investigations of methods to extend the useful calibration range revealed reduced vapour-phase temperatures in the presence of a convective gas flow during atomisation, and a greater potential for errors using non-resonance lines. With respect to the latter, the absorbance signal is much more sensitive to matrix induced changes in the temperature interval in which atoms are formed compared to resonance lines. Furthermore, at the lead 261.4 nm non-resonance line we observed overcompensation errors caused by cobalt when using a Zeeman-effect system, and undercorrection due to the AlCl(g) molecule with a continuum source background corrector.     

Direct determination of bromine in plastic materials by means of solid sampling high-resolution continuum source graphite furnace molecular absorption spectrometry

This work investigates the potential of high-resolution continuum source graphite furnace molecular absorption spectrometry for the direct determination of bromine in polymers, which could be interesting in view of the current regulations restricting the use of organobrominated compounds. The method developed is based on the addition of Ca (300 μg) and Pd (30 μg) to favor the formation of CaBr, which is monitored at the main molecular “lines” (rotational spectra) found in the vicinity of 625.315 nm.It was found that accurate results could be obtained for all the samples investigated (polyethylene, polypropylene and acrylonitrile butadiene styrene certified reference materials) using any of the lines studied and constructing the calibration curve with aqueous standards. Furthermore, the combined use of the main four CaBr lines available in the spectral area simultaneously monitored permits to easily expand the linear range up to 2000 ng, provides a limit of detection of 1.8 ng (1.8 μg g^− 1 for a mass of 1 mg) and further improves precision to values between 3–7% RSD. Overall, the method proposed seems suited for the fast and simple control of these types of samples (approximately 10 min for sample are required), circumventing the traditional problems associated with sample digestion (e.g., losses of volatile compounds), and providing sufficient sensitivity to easily comply with regulations.     

Unusual calibration curves observed for iron using high-resolution continuum source graphite furnace atomic absorption spectrometry

The simultaneous determination of cadmium and iron in plant and soil samples has been investigated using high-resolution continuum source graphite furnace atomic absorption spectrometry. The primary cadmium resonance line at 228.802 nm and an adjacent secondary iron line at 228.726 nm, which is within the spectral interval covered by the charge-coupled device (CCD) array detector, have been used for the investigations. Due to the very high iron content in most of the soil samples the possibility has been investigated to reduce the sensitivity and extend the working range by using side pixels for measurement at the line wings instead of the line core. It has been found that the calibration curves measured at all the analytically useful pixels of this line consisted of two linear parts with distinctly different slopes. This effect has been independent of the positioning of the wavelength, i.e., if the Cd line or the Fe line was in the center of the CCD array. The most likely explanation for this unusual behavior is a significant difference between the instrument width Δλ_Instr and the absorption line width Δλ_Abs, which is quite pronounced in the case of Fe. Using both parts of the calibration curves and simultaneous measurement at the line center and at the wings made it possible to extend the working range for the iron determination to more than three orders of magnitude.     

Determination of manganese in brain samples by slurry sampling graphite furnace atomic absorption spectrometry

A simple procedure for the determination of manganese in different sections of human brain samples by graphite furnace atomic absorption spectrometry has been developed. Brain sections included cerebellum, hypothalamus, frontal cortex, vermix and encephalic trunk. Two sample preparation procedures were evaluated, namely, slurry sampling and microwave-assisted acid digestion. Brain slurries (2% w/v) could be prepared in distilled, de-ionized water, with good stability for up to 30 min. Brain samples were also digested in a domestic microwave oven using 5 ml of concentrated HNO₃. A mixed palladium+magnesium nitrate chemical modifier was used for thermal stabilization of the analyte in the electrothermal atomizer up to pyrolysis temperatures of 1300 °C, irrespective of the matrix. Quantitation of manganese was conducted in both cases by means of aqueous standards calibration. The detection limits were 0.3 and 0.4 ng ml⁻¹ for the slurry and the digested samples, respectively. The accuracy of the procedure was checked by comparing the results obtained in the analysis of slurries and digested brain samples, and by analysis of the NIST Bovine Liver standard reference material (SRM 1577a). The ease of slurry preparation, together with the conventional set of analytical and instrumental conditions selected for the determination of manganese make such methodology suitable for routine clinical applications.     

Noble metals as permanent chemical modifiers for the determination of mercury in environmental reference materials using solid sampling graphite furnace atomic absorption spectrometry and calibration against aqueous standards

Iridium, palladium, rhodium and ruthenium, thermally deposited on the platform, were investigated as permanent modifiers for the determination of mercury in ash, sludge, marine and river sediment reference materials, ground to a particle size of 50 μm, using solid sampling graphite furnace atomic absorption spectrometry. A total mass of 250 μg of each modifier was applied using 25 injections of 20 μl of modifier solution (500 mg l⁻¹), and executing a temperature program for modifier conditioning after each injection. The performance of palladium was found to be most consistent, taking the characteristic mass as the major criterion, resulting in an excellent correlation between the measured integrated absorbance values and the certified mercury contents. Mercury was found to be lost in part from aqueous solutions during the drying stage in the presence of all the investigated permanent modifiers, as well as in the presence of the palladium and magnesium nitrates modifier added in solution. A loss-free determination of mercury in aqueous solutions could be reached only after the addition of potassium permanganate, which finally made possible the use of aqueous standards for the direct analysis of solid samples. A characteristic mass of 55–60 pg Hg was obtained for the solid samples, using Pd as a permanent modifier, and also in aqueous solutions after the addition of permanganate. The results obtained for mercury in ash, sludge and sediment reference materials, using direct solid sapling and calibration against aqueous standards, as well as the detection limit of 0.2 mg kg⁻¹ were satisfactory for a routine procedure.     

A direct solid sampling electrothermal atomic absorption spectrometry method for the determination of silicon in biological materials

A solid sampling electrothermal atomic absorption spectrometry method for direct determination of trace silicon in biological materials was developed and applied to analysis of pork liver, bovine liver SRM 1577b and pure cellulose. The organic matrix was destroyed and expelled from the furnace in the pyrolysis stage involving a step-wise increasing the temperature from 160 °C to 1200 °C. The mixed Pd/Mg(NO₃)₂ modifier has proved to be the optimum one with respect to the achievement of maximum sensitivity, elimination of the effect of the remaining inorganic substances and the possibility of using calibration curves measured with aqueous standard solutions for quantification. For the maximum applicable sample amount of 6 mg, the limit of detection was found to be 30 ng g^− 1. The results were compared with those obtained by different spectrometric methods involving sample digestion, by electrothermal atomic absorption spectrometry using slurry sampling, by wavelength dispersive X-ray fluorescence spectrometry and by radiochemical neutron activation analysis. The method seems to be a promising one for analysis of biological materials containing no significant fraction of silicon in form of not naturally occurring volatile organosilicon compounds. The still incessant serious limitations and uncertainties in the determination of trace silicon in solid biological materials are discussed.     

Determination of cadmium,copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry

Solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated as a potential technique for the routine determination of trace elements in mineral coal and cadmium, copper and lead were chosen as the model elements. Cadmium and lead could be determined at their main resonance lines at 228.8 nm and 283.3 nm, respectively, but an alternate, less sensitive line had to be used for the determination of copper because of the high copper content in coal. No modifier was necessary for the determination of copper and calibration against aqueous standards provided sufficient accuracy of the results. For the determination of cadmium and lead two different modifiers were investigated, palladium and magnesium nitrates in solution, added on top of each sample aliquot before introduction into the atomizer tube, and ruthenium as a ‘permanent’ modifier. Both approaches gave comparable results, and it is believed that this is the first report about the successful use of a permanent chemical modifier in SS-GF AAS. Calibration against solid standards had to be used for the determination of cadmium and lead in order to obtain accurate values. The agreement between the values found by the proposed procedure and the certificate values for a number of coal reference materials was more than acceptable for routine purposes. The detection limits calculated for 1 mg of coal sample using the ‘zero mass response’ were 0.003 and 0.007 μg g⁻¹ for cadmium with the permanent modifier and the modifier solution, respectively, approximately 0.04 μg g⁻¹ for lead, and 0.014 μg g⁻¹ for copper.