Simultaneous Determination of Metals in Coal with Low-Resolution Continuum Source Atomic Absorption Spectrometer and Filter Furnace Atomizer

The setup including low-resolution spectrometer with the charge-coupled device (CCD) detector, continuum radiation source and filter furnace (FF) atomizer was employed for direct simultaneous determination of Al, Fe, Mg, Cu and Mn in coal slurry. In the FF, sample vapour entered absorption volume by filtering through heated graphite. Absorption spectrum within 200–400 nm was repeatedly recorded during the atomization period with spectral resolution 0.3 nm. The output of the CCD elements was measured within each spectrum, atomic absorption at specific wavelengths measured and corrected with respect to the linearization algorithm, and integrated. Calibration was performed using carbon slurry impregnated by the analyte metals as well as with the analytes added to the slurries as multi-element solutions. The comparison showed preference of the second method, which provides for 60 % of measurements the results within 10 % deviation range from the certified reference data independent of concentration of the analyte. Low-resolution spectral instrument with fast CCD detection makes possible simultaneous detection of transient absorption signals for several elements. The use of continuum light source makes it possible to determine broad range of concentrations without slurry dilution.Keywords: Coal slurry, electrothermal atomic absorption spectrometry, simultaneous multi-element determination, filter furnace atomize

Simultaneous Multi-Element Electrothermal Atomic Absorption Determination Using a Low Resolution CCD Spectrometer and Continuum Light Source: The Concept and Methodology

A low resolution CCD spectrometer with continuum light source and fast-heated graphite tube atomizer was employed for simultaneous multi element determination by electrothermal atomic absorption spectrometry (SMET AAS). The sample vaporization pulse was monitored by fast scanning of vapour spectra within the 190–410 nm wavelength range; absorption was measured at the CCD pixels corresponding to atomic resonance lines; function absorbance vs. concentration of atomic vapour was automatically linearized, and the modified signals integrated. The setup consisted of a D2 or Xe arc lamp, a spectral instrument with a half-width of transmittance profile 120 pm, a linear CCD array attached to a PC and a tube atomizer furnished with a carbon fibre collector. In the experiments simultaneous determination of 18 elements was performed in the mixed solutions at the mg L–1 to μg L–1 level, within 4–4.5 orders of magnitude linear concentration range. About 1–2 min was needed for the measurement and calculation. Limits of detection (LOD) for individual elements were 1.5–2 orders of magnitude higher than those in the single element ET AAS, but similar or below those in flame AAS. Further reduction of LODs and correction of possible spectral and chemical interferences are associated with optimization of the light source and atomization programme and modification of the calculation algorithm.Keywords: Electrothermal Atomic Absorption Spectrometry, Simultaneous Multi-element Determination, CCD Spectrometer, Fast-heated Graphite Tube Atomize

Making ET AAS Determination Less Dependent on Vapourization Kinetics of the Analytes

The quantification of the analytes in ET AAS is normally attained by the measurement and integration of transient absorbance. High degree of atomization and constant vapour transportation rate for the analyte atoms in the absorption volume are considered to be crucial to grant correctness of the measurements. However, the second of these conditions has, in fact, never been met in the commercial tube or tube-platform ET atomizers. The vapourization of the analyte occurs during temperature rise that affects vapour transport; vapourization temperature depends on matrix or presence of chemical modifier. In the analytical practice, the problem is normally bypassed by using reference materials with physical and chemical properties similar to those of the sample. The general solution of the problem comes from the integration of running absorbance normalized with regard to vapour transportation velocity. In this work, the approach was verified by measuring absorption signals for Ag, Cd, Mn, Pb and Tl in the tube atomizer (without a platform), monitoring the temperature of the tube and calculating the instantaneous velocity of vapour transfer and respective integration. The semi-empirical formula employed to describe vapour transport velocity included the diffusion parameters specific for each element and a common constituent, attributed to gas expansion. The measurements and numerical integration were performed using various temperature ramps for the analytes alone and those introduced together with excessive amounts of Mg and Pd. The methodology suggested reduced the error associated with change of atomization kinetics from 20 to 2 %. In combination with chemical modification the measurement methodology does not require platform atomization.KEYWORDS ET AAS, vapour transport, chemical modification, normalization of integrated absorbanc

Spectrochimica acta part b-antomic spectroscopy

Acesso restrito: Texto completo.In the present work a direct method for the determination of arsenic in petroleum derivatives has been developed, comparing the performance of a commercial transversely heated platform atomizer (THPA) with that of a transversely heated filter atomizer (THFA). The THFA results in a reduction of background absorption and an improved sensitivity as has been reported earlier for this atomizer. The mixture of 0.1% (m/v) Pd+0.03% (m/v) Mg+0.05% (v/v) Triton X-100 was used as the chemical modifier for both atomizers. The samples (naphtha, gasoline and petroleum condensate) were stabilized in the form of a three-component solution (detergentless microemulsion) with the sample, propan-1-ol and 0.1% (v/v) HNO3 in a ratio of 3.0:6.4:0.6. The characteristic mass of 13 pg found in the THFAwas about a factor of two better than that of 28 pg obtained with the THPA; however, the limits of detection (LOD) and quantification (LOQ) were essentially the samefor both atomizers (1.9 and 6.2 μg L−1, respectively, for THPA, and 1.8 and 5.9 μg L−1, respectively, for THFA) due to the increased noise observed with the THFA. A possible explanation for that is a partial blockage of the radiation from the hollow cathode lamp by the narrow inner diameter of this tube and the associated loss of radiation energy. Due to the lack of an appropriate certified reference material, recovery tests were carried out with inorganic and organic arsenic standards and the resultswere between 89% and 111%. The only advantage of the THFA found in this work was a reduction of the total analysis time by about 20% due to the ‘hot injection’ that could be realized with this furnace. The arsenic concentrations varied from bLOQ to 43.3 μg L−1 in the samples analyzed in this work