Multi-element Electrothermal Atomic Absorption Spectrometry Research Articles

Low-resolution continuum source simultaneous multi-element electrothermal atomic absorption spectrometry: steps into practice

The theory and practical problems of continuum source simultaneous multi-element electrothermal atomic absorption spectrometry (SMET AAS) are discussed by the example of direct analysis of underground water. The experimental methodology is based on pulse vaporization of the sample in a fast heated graphite tube and measurement of transient absorption of continuum spectrum radiation from D2 and Xe lamps within 200–400nm wavelengths range with a low resolution spectral instrument and linear charge-coupled device. The setup permits the acquisition of 200 spectra during 1s atomization pulse. Respective data matrix absorbance vs wavelength/time is employed for the quantification of elements in the sample. The calculation algorithm developed includes broad band and continuum background correction, linearization of function absorbance vs. concentration of atomic vapor and integration of thus modified absorbance at the resonance lines of the elements to be determined. Practical application shows that the method can be employed for the direct simultaneous determination of about 20 elements above microgram per liter level within 3–5 orders of the magnitude concentration range. The investigated sources of measurement errors are mainly associated with the atomization and vapor transportation problems, which are aggravated for the simultaneous release of major and minor sample constituents. Respective corrections concerning the selection of analytical lines, optimal sampling volume, matrix modification and cleaning of the atomizer have been introduced in the SMET AAS analytical technology. Under the optimized experimental conditions the calibration curves in Log-Log coordinates for all the investigated analytes in the single or multi-element reference solutions are approximated by the first order equations. The use of these equations as permanent characteristics of the setup enables instant quantification of Al, Ca, Co, Cr, Cu, Fe, Mg, Mn and Ni in the underground water samples with an accuracy of 30%.

Determination of As in particulate matter using Se as an internal standard by multi-element electrothermal atomic absorption spectrometry

In this study Se has been evaluated as a potential internal standard for the determination of As in particulate matter using multi-element electrothermal atomic absorption spectrometry.

Application of zirconium–iridium permanent modifier for the simultaneous determination of lead, cadmium, arsenic, and nickel in atmospheric particulate matter by multi-element electrothermal atomic absorption spectrometry

A novel and robust method for the simultaneous determination of lead, cadmium, arsenic, and nickel in atmospheric particulate matter by multi-element electrothermal atomic absorption spectrometry was developed, using zirconium-iridium coating as permanent modifier (140μg Zr and 4μg Ir). After 300 atomization cycles, it was necessary to add 2μg of Ir. Due to the varying concentrations of Pb in atmospheric particulate matter, lead was monitored at two wavelengths, at the less sensitive line of 261.4nm for high concentration samples (>20μg L(-1)) or at 283.3nm for the low concentration samples. Matrix-matched calibration had to be performed for quantitative recoveries (96-102%). Following this approach, the four elements were determined in atmospheric particulate matter samples from an industrial area near the city of Athens in two different time periods (cold-warm) with limits of detection of 5.5ng m(-3) for Pb at 261.4nm and 0.29ng m(-3) at 283.3nm, 0.019ng m(-3) for Cd, 0.14ng m(-3) for As, and 0.22ng m(-3) for Ni. Lead, Cd, and As levels were very low, whereas Ni content was at comparable levels with other areas worldwide.

Design considerations regarding an atomizer for multi-element electrothermal atomic absorption spectrometry

The methodology of simultaneous multi-element electrothermal atomic absorption spectrometry (ETAAS-Electrothermal Atomic Absorption Spectrometry) stipulates rigid requirements to the design and operation of the atomizer. It must provide high degree of atomization for the group of analytes, invariant respective to the vaporization kinetics and heating ramp residence time of atoms in the absorption volume and absence of memory effects from major sample components. For the low resolution spectrometer with a continuum radiation source the reduced compared to traditional ETAAS (Electrothermal Atomic Absorption Spectrometry) sensitivity should be, at least partially, compensated by creating high density of atomic vapor in the absorption pulse. The sought-for characteristics were obtained for the 18 mm in length and 2.5 mm in internal diameter longitudinally heated graphite tube atomizer furnished with 2–4.5 mg of ring shaped carbon fiber yarn collector. The collector located next to the sampling port provides large substrate area that helps to keep the sample and its residue in the central part of the tube after drying. The collector also provides a “platform” effect that delays the vaporization and stipulates vapor release into absorption volume having already stabilized gas temperature. Due to the shape of external surface of the tube, presence of collector and rapid (about 10 °C/ms) heating, an inverse temperature distribution along the tube is attained at the beginnings of the atomization and cleaning steps. The effect is employed for cleaning of the atomizer using the set of short maximum power heating pulses. Preparation, optimal maintenance of the atomizer and its compliance to the multi-element determination requirements are evaluated and discussed. The experimental setup provides direct simultaneous determination of large group of element within 3–4 order concentration range. Limits of detection are close to those for sequential single element determination in Flame AAS with primary line source that is 50–1000 times higher than the limits obtainable with common ETAAS (Electrothermal Atomic Absorption Spectrometry) instrumentation.

Simultaneous determination of lead, nickel, tin and copper in aluminium-base alloys using slurry sampling by electrical discharge and multielement ETAAS

The simultaneous multielement determination of Pb, Sn, Ni and Cu in aluminium alloys by electrothermal atomic absorption spectrometry (ETAAS) was performed by a quick method using slurry sampling. The metallic colloidal slurries were obtained by an electrical discharge operated in liquid medium. In this work, the effects of aluminium were evaluated and the results show that it causes a strong retention of Pb, Ni and Cu at low pyrolysis temperatures which is overcome by employing high pyrolysis temperatures. Aluminium also significantly improves the thermal stabilisation of Pb and Sn, it being possible to reach pyrolysis temperatures of 1100 and 1300 °C, respectively. Such stabilisation indicates that the performance of aluminium as a matrix modifier for Pb is better than that obtained using phosphate and magnesium nitrate without substantial changes of the figures of merit. The effects of aluminium on the atomisation characteristics of the elements and those coming from the simultaneous multielement determination on the figures of merit of the elements are also discussed. In this work, a calibration procedure involving a matrix matching method with aqueous aluminium standards is proposed as a simple and efficient way to solve the inconveniences originated by the aluminium matrix. The proposed method was applied to the simultaneous multielement determination of several aluminium-base alloy standards giving results well within the recommended values.

Multielement electrothermal atomic absorption spectrometry: a study on direct and simultaneous determination of chromium and manganese in urine.

A study was carried out on the direct determination of Cr and Mn in urine using simultaneous atomic absorption spectrometry (SIMAAS). The heating program conditions, the absorbance signal profiles, the influence of different chemical modifiers, and the urine sample volume delivery into the tube were optimized to perform the calibration with aqueous solutions. Among several chemical modifiers tested, the best recovery and repeatability results were obtained for 3 microg Mg(NO3)2. On using this modifier, the pyrolysis and atomization temperatures for simultaneous determination of Cr and Mn were 1,300 degrees C and 2,500 degrees C, respectively. Urine samples were diluted (1+1) with 2.0% (v/v) HNO3 + 0.05% (w/v) Triton X-100 prepared in high purity water. A 20-microL aliquot of analytical solution and 10 microL of chemical modifier solution were delivered to the graphite tube. The characteristic masses were 7.8 pg for Cr (RSD=4.0%) and 4.6 pg for Mn (RSD=2.6%). The limits of detection were 0.08 microg L(-1) (n=20, 3s) for Cr and 0.16 microg L(-1) (n=20, 3s) for Mn. Recovery studies for 1.0 or 2.5 microg L(-1) of Cr and Mn added to different urine samples showed acceptable results for Cr (100%, RSD=14%) and Mn (88%, RSD=5.6%).

Determination of Lead, Cadmium, Arsenic and Nickel in Atmospheric Particulate Matter by Simultaneous Multi-Element Electrothermal Atomic Absorption Spectrometry

A simple method for the determination of lead, cadmium, arsenic and nickel in atmospheric particulates by simultaneous multi-element Electrothermal Atomic Absorption Spectrometry has been developed. Due to the high concentrations of Pb and low concentrations of Cd, As and Ni found in particulate matter, lead was monitored at 261.4 nm and the other analytes at the usual wavelengths. Two approaches have been compared using aqueous standard solutions and acid extracts of particulate matter samples. First, a fast electrothermal programme, without chemical modifier, and a short pyrolysis step at 500°C for 10 s, has been developed. The omission of the pyrolysis step was not possible, because strong interference on arsenic was observed. The characteristic masses determined with this approach were 2.10 ng for Pb, 2.0 pg for Cd, 35.8 pg for As and 27.5 pg for Ni. The corresponding detection limits were 4.2 μg l−1 (Pb), 0.025 μg l−1 (Cd), 0.42 μg l−1 (As) and 1.5 μg l−1 (Ni), respectively. The second approach utilized the addition of Pd/Mg modifier (5 μg + 5 μg). The pyrolysis temperature (Tpyr) could be raised up to 650°C. The characteristic masses were 1.40 ng (Pb), 2.2 pg (Cd), 37.3 pg (As) and 27.9 pg (Ni). In the presence of Pd/Mg modifier the limits of detection were 4.3 μg l−1 (Pb), 0.020 μg l−1 (Cd), 0.26 μg l−1 (As) and 0.97 μg l−1 (Ni), respectively. These two approaches were applied in the determination of Pb, Cd, As and Ni in atmospheric particulates. Matrix matched calibration was used in order to achieve accurate and precise results. The calculated recoveries, in the absence of chemical modifiers, were 128% for Pb, 124% for Cd, 108% for As and 110% for Ni. The calculated recoveries were consistently better in the presence of the mixed Pd/Mg modifier: 101% (Pb), 99.7% (Cd), 103% (As) and 102% (Ni), respectively.

Performances and practical applications of simultaneous multi-element electrothermal atomic absorption spectrometry the case of the SIMAA 6000

The Perkin-Elmer SIMAA 6000 ET-AAS system was studied in the simultaneous multi-element mode with respect to sensitivity and detection limits. Calibration curves were established for Co, Cu, Pb and Cd using standard and end-capped THGA tubes. Due to the very low noise of the solid-state detector used, uncommon detection limits were obtained, particularly for volatile elements. The sensitivities observed were similar to those obtained with a 4100ZL system, in concordance with the data published by the manufacturer. The possibility of measurement of very low absorbance signals has revealed an increase of the calibration curve slope near detection limits and thus an enhancement of the sensitivity for low analyte masses. This concerns volatile elements only (Pb, Cd) measured using a standard THGA tube; with the end-capped tube, the calibration curves become practically straight lines. Using a fast program approach and simple calibration procedure, simultaneous multielement analysis of several environmental reference materials has given results in good agreement with recommended values.

Test of the generalized standard addition method and linearization algorithms for the direct, simultaneous, multi-element analysis of solid samples by electrothermal atomic absorption spectrometry

The application of a multi-element electrothermal atomic absorption spectrometry (ETAAS) instrument with line sources and Zeeman-effect background correction to the direct, simultaneous determination of Ag, Cd, Cr and Pb in solid reference materials is described. Due to the occurrence of interference effects, the generalized standard addition method (GSAM) was required for calibration purposes. In order to extend the dynamic range for analytes present at high concentrations, linearization algorithms were tested. The combination of the GSAM and extension of the linear range, when necessary, generally yielded acceptable analytical results for the suite of elements studied, and may provide a useful approach to calibration in the direct analysis of solid samples by multi-element ETAAS. However, while linearization yielded good results for Ag and Cd in solid reference materials, it remains to be demonstrated that acceptable performance can be obtained for other elements in real samples.

Solid state detector for simultaneous multi-element electrothermal atomic absorption spectrometry with Zeeman-effect background correction

The development and characterization is described of a solid-state detector for simultaneous multielement electrothermal atomic absorption spectrometry (ETAAS) using combined line sources. Photodiode technology providing high quantum efficiency is married to a complementary metal oxide semiconductor (CMOS) charge amplifier array for low noise output. Thus a large surface (3 cm × 6 cm) detector including 60 individual photodiodes can be produced using a high yield-high reliability process to meet the requirements of a simple optical design which has the disadvantage of a large focal plane but the advantages of high throughput and reasonable cost. An evaluation of the opto-electrical characteristics of the detector is described. The significance of the results to applications in ETAAS is discussed.

Determination of scandium, yttrium and eight rare earth elements in silicate rocks and six new geological reference materials by simultaneous multi-element electrothermal atomic absorption spectrometry with Zeeman-effect background correction

A method was developed for the simultaneous determination of a group of four rare earth elements (REE) in one firing using a multi-element graphite furnace atomic absorption spectrometer. The instrument can be programmed for automatic determination of an additional four REE elements in a second group by two firings. The sensitivities with a pyrolytic graphite coated graphite tube furnace are sufficiently high to permit the determination of low-µg g–1 amounts of Y, Nd and Sm and ng g–1 amounts of Sc, Eu, Dy, Ho, Er, Tm and Yb in silicate rocks from as little as 0.1 g or less of sample concentrate in a 1 ml final volume. After dissolution of the sample in acids, Sc, Y and the REE were preconcentrated by cation-exchange chromatography or coprecipitation with calcium oxalate and hydrated iron oxide carriers and determined by the proposed method. The interferences due to the presence of trace amounts of common metals in the ion-exchange concentrates were corrected for with Zeeman-effect background correction. Inter-method correlation plots for electrothermal atomic absorption spectrometry (ETAAS)versus inductively-coupled plasma mass spectrometry (ICP-MS) values and for oxalate versus ion-exchange recovery results for REE showed good agreement. Satisfactory results were obtained for Sc, Y and eight REE in three international reference rocks, MRG-1, SY-2 and NIM-G. The method was applied to the determination of these elements in six new candidate reference rocks of the Canadian Certified Reference Materials Project. In most instances the ETAAS results compared satisfactorily with those obtained independently by inductively coupled plasma atomic emission spectrometry (ICP-AES) and ICP-MS.