Correction of characteristic mass in Zeeman graphite furnace atomic absorption spectrometry

A systematic study has been made of the effect of hollow-cathode lamp current and slit width (SW) of the 4100ZL spectrometer on characteristic mass m₀, Zeeman sensitivity ratio R, and roll-over absorbance A_r, for nine elements: Au, Bi, Cd, Co, Cu, Mn, Ni, Pb and Tl. The lamp spectra near the recommended analytical lines have been investigated for these elements. The data obtained have been combined with a theoretical analysis to show that the self-absorption of the analytical lines observed with increasing current and the rise of non-absorbable radiation with increasing SW affect m₀ and the A_r and R parameters differently. It is shown that a separate correction requiring additional narrow-slit measurement of the A_r parameter is necessary to take into account the SW effect on m₀. A separate-correction method built upon this basis offers a substantial improvement of the accuracy of taking into account the SW effect on m₀ compared with the method of combined correction proposed earlier (E.G. Su, A.I. Yuzefovsky, R.G. Michel, J.T. McCaffrey and W. Slavin, Microchem. J., 48 (1993) 278). Exceptions are the Mn and Ni analytical lines, for which the m₀ correction has turned out to be ineffective both in the separate- and combined-correction procedures because of adjacent absorption-sensitive lines passing through the wider slit.     

Precision and detection limits in Zeeman graphite furnace atomic absorption spectrometry

This is the first theoretical study of photometric errors in Zeeman graphite furnace atomic absorption spectrometry with evaluation of their effect on the precision in the traditional method of peak area determination and the pulse restoration method proposed earlier for linearization and expansion of calibration curves. Besides the fraction of non-absorbed radiation, α, and Zeeman sensitivity ratio, R, the theoretical calculations make use of three more parameters, namely the “energy” value, E, the baseline offset compensation time, t_toc, and the integration time, t_int. The theoretical calculations are supported by experimental data on detection limits for a number of elements and on the RSD obtained in Ag and Cd determinations. A comparison of the precision in the case of pulses with dips has shown the pulse restoration method to be superior over the traditional technique. The theoretical results can be used to improve the measurement precision and the detection limits by proper modification of the spectrophotometer and optimization of experimental conditions.     

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.     

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.     

Preconcentration of lead in biological matrices for graphite furnace atomic absorption spectrometry

Lead was transferred by a two-step extraction procedure from complicated biological matrices into an aqueous solution. Thereafter, lead could be accurately determined in the aqueous solution without interference by graphite furnace atomic absorption spectrometry (GFAAS). Biological samples were digested sequentially by a mixture of sulphuric acid and nitric acids and a strong oxidant, potassium peroxodisulphate. Lead was extracted by dithiocarbamate in chloroform from the digest solution and subsequently back-extracted into a mercury(II) solution. Matrix materials such as chloride, phosphate and sulphate, which were known to cause serious interference in the determination of lead by GFAAS, could be eliminated in the preconcentration procedure. Close to 90% recovery of lead was achieved. The proposed procedure was applied for the analysis of several NBS biological standard reference materials containing lead in the mg kg^?1 range and satisfactory results were obtained.     

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.     

石墨炉原子吸收光谱法测定茶叶中的铅

采用石墨炉原子吸收光谱法测定茶叶中铅,以NH4H2PO4作为基体改进剂,提高了测定的灰化温度,消除了基体干扰.方法简便,快速,准确度高.通过对标准物质的多次测定,结果均在其保证值范围内,相对标准偏差为2.8%.对样品进行加标回收试验,回收率为96%～105%,方法检出限为0.12μg/L.     

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.     

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.     

Determination of traces of silver in copper by direct Zeeman graphite furnace atomic absorption spectrometry

Summary A method was developed to determine traces of silver in copper by direct Zeeman graphite furnace atomic absorption spectrometry (ZAAS) on solid samples. The system is calibrated using quantitatively doped copper, whose blank silver content is determined using an iterative process. The method has been applied to the analysis of several candidate reference materials. Relative standard deviations of 2 to 5% are obtained in the range 1 to 12 g·g^–1. Furthermore, it was also applied to assess the homogeneity of a neutron dosimetry candidate reference material.     

石墨炉原子吸收法快速测定血液中铅和镉

建立了快速测定血液中铅和镉的石墨炉原子吸收光谱法。使用5%硝酸溶液对样品进行脱蛋白处理,然后在旋涡混合器上振摇,离心后取上清液上石墨炉原子吸收进行测定。 结果表明,Pb、Cd工作曲线线性关系良好,相关系数均大于0.9994;方法检出限分别为4.32μg/L和0.27μg/L;Pb的回收率为91.60%～97.31%,镉的回收率为97.04%～98.86%;Pb测定的RSD（n=7）为2.35%,Cd测定的RSD（n=7）为1.53%。冻干牛血铅、镉标准物质GBW09139k和GBW09140k的测定值与参考值吻合。该方法快速准确,精密度、准确度、检出限等测定结果令人满意。可以作为日常血铅、血镉的检测的方法。     

Determination of lead in geological and biological materials by graphite furnace atomic absorption spectrometry

Summary Serious systematic errors inherent in the determination of lead in geological and biological samples by flameless atomic-absorption spectrometry are demonstrated. The reduced absorption of lead is due to partial interaction with alkaline, alkaline-earth and iron chlorides during the atomization stage. Incomplete dissociation of the volatile monochloride of lead in the gaseous phase reduces the absorption signal. An addition of 20% hydrogen to nitrogen (purge gas) diminishes signal suppression by removing the chlorine in form of volatile HCl. The detection limit is about 0.6 ppm in rocks and about 0.3 ppm in plant materials. Depending on the content in the samples the relative standard deviation is between 1 and 12%. The accuracy of the method was tested on 39 international standard reference samples.

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Bestimmung von Blei in geologischen und biologischen Materialien durch AAS mit der Graphitrohrküvette

Zusammenfassung Schwerwiegende systematische Fehler bei der Bestimmung von Blei in geologischen und biologischen Materialien mit der Graphitrohrküvette werden aufgezeigt. Die Reaktion von Blei mit Alkali-, Erdalkali- und Eisenchloriden während der Atomisierungsphase führt zur Bildung von Bleimonochlorid, das nur unvollständig dissoziiert und eine Signalunterdrückung zur Folge hat. Ein Zusatz von 20% Wasserstoff zu Stickstoff als Spülgas vermindert die Signalunterdrückung, indem überschüssiges Chlor als Chlorwasserstoff entfernt wird. Die Nachweisgrenze liegt bei ca. 0,6 ppm für Gesteine und bei ca. 0,3 ppm für Pflanzenmaterialien. Je nach der Konzentration beträgt die relative Standardabweichung 1–12%. Die Genauigkeit der Methode wurde an 39 internationalen Standardreferenzproben überprüft.

     

Instrumentation for simultaneous multielement atomic absorption spectrometry with graphite furnace atomization

Graphite furnace-atomic absorption spectrometry (GF-AAS) is restricted to the determination of 4 to 6 elements simultaneously due to the limitations of hollow cathode lamps. However, a consideration of prototype continuum source instruments and recent advances in the fields of spectrometer and detector technology suggests that a multielement GF-AAS instrument, with the multielement versatility associated with atomic emission spectrometry, is possible. Such a multielement instrument would employ a continuum source and provide 1.) multielement determinations for 30 to 40 elements, 2.) wavelength and time integrated absorbance measurements which are independent of the source width, 3.) detection limits comparable to line source AAS with the potential for another order of magnitude improvement using atomization at elevated pressures, 4.) extended calibration ranges limited only by the memory of the atomizer, and 5.) high resolution inspection of the spectra surrounding the analytical wavelength. Such an instrument could provide figures of merit comparable to inductively coupled plasma-mass spectrometer with considerably less complexity.     

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     

石墨炉原子吸收法测定钢中铅的干扰抑制

研究了石墨炉原子化法测定钢铁中痕量铅的干扰情况，并进行了干扰抑制实验。提出了抑制干扰的方法。     

Determination of tin and lead in sediment slurries by graphite furnace atomic absorption spectrometry

Methods were determined for lead and tin determinations in river, marine and lake sediments by slurry sampling and graphite furnace atomic absorption spectrometry. The optimizations were carried out using River Sediment BCR 320 and Marine Sediment PACS-2 for Pb and Sn, respectively. For Pb determination, the parameters studied included inorganic acid mixture, stabilizing agent, sample mass and sonication time. The influence of diluents and the extraction to the liquid phase for two different matrices was evaluated for Sn. The Pb content in the slurry liquid phase was ca. 56%, and ranged from 75% to 100% for Sn. Representative masses of 34 and 45 mg, and effective masses of 12 and 48 μg for Pb and Sn, respectively, were obtained under optimized conditions. Detection and quantification limits of 0.2 and 0.7 μg g⁻¹ for Pb, and 1.5–2.6 and 4.5–7.6 μg g⁻¹ for Sn were obtained.

     

微波消解-石墨炉原子吸收光谱法测定纸质包装材料中铅含量

建立了微波消解-石墨炉原子吸收光谱法测定纸质包装材料中铅含量的方法.该方法具有良好线性关系,线性相关系数R~2为0.999 5,检出限为0.028μg/L,回收率为97%~102%,其相对标准偏差在3.14%~5.76%之间,优点为检出限低、精密度好、准确度高,能精确测定纸质包装材料中的铅含量.     

Instrumentation for simultaneous multielement atomic absorption spectrometry with graphite furnace atomization

Graphite furnace-atomic absorption spectrometry (GF-AAS) is restricted to the determination of 4 to 6 elements simultaneously due to the limitations of hollow cathode lamps. However, a consideration of prototype continuum source instruments and recent advances in the fields of spectrometer and detector technology suggests that a multielement GF-AAS instrument, with the multielement versatility associated with atomic emission spectrometry, is possible. Such a multielement instrument would employ a continuum source and provide 1.) multielement determinations for 30 to 40 elements, 2.) wavelength and time integrated absorbance measurements which are independent of the source width, 3.) detection limits comparable to line source AAS with the potential for another order of magnitude improvement using atomization at elevated pressures, 4.) extended calibration ranges limited only by the memory of the atomizer, and 5.) high resolution inspection of the spectra surrounding the analytical wavelength. Such an instrument could provide figures of merit comparable to inductively coupled plasma-mass spectrometer with considerably less complexity.