Van T. Luong

Comparison of the energetics of desorption of solution and vapour phase deposited analytes in graphite furnace atomic absorption spectrometry

The energetics of atomisation of Pb, Cu, Ag and Au in pyrolytic graphite coated, uncoated electrographite and glassy carbon tubes was studied following deposition of the analyte as a solution (primary site) and as an aerosol vapour (secondary site). Arrhenius activation energies (Ea) for Pb and Cu were independent of tube type and mode of analyte deposition. An apparent first-order rate of release occurs from all tube types and from both primary-and secondary-deposition sites, suggesting that both elements desorb from the surface as individual atoms. Values of Ea for desorption of Ag and Au were independent of furnace tube type but dependent on the deposition mode, with fractional orders of desorption obtained throughout. Data for these elements suggest the formation of micro-droplets or caps (primary site) and islands (secondary site) with desorption occurring from the droplet surface or at the metal-graphite interface.

Characteristic temperatures in a FAPES source

Abstract A number of state distribution temperatures were measured in an effort to characterize a 100 W 13.56 MHz rf He plasma established in a FAPES (Furnace Atomization Plasma Emission Spectrometry) source. Excitation temperatures derived from a Boltzmann plot of He I and Fe I lines were in reasonable agreement, i.e. 3300 ± 180 and 2920 ± 180 K, respectively. An excitation temperature measured with Fe II lines was substantially larger than the above values, being 7610 ± 450 K. A kinetic or Doppler temperature based on measurement of the width of the Be I 234.861 nm line profile was 7030 ± 1150 K whereas the He ionization temperature derived from the measured electron number density was 10920 ± 1900 K. It is clear that complete LTE does not exist in this source

Influence of the Generator Frequency on the Analytical Characteristics of FAPES

A preliminary study of the influence of generator frequency on the operating and analytical characteristics of atmospheric-pressure rf He and Ar plasmas in a FAPES (Furnace Atomization Plasma Emission Spectrometry) system is presented. Apparent forward powers of 50 W were used to establish He plasmas at 13.6,27,40, and 54 MHz and Ar plasmas at 27 and 40 MHz. He and Ar excitation temperatures were of comparable magnitude (∼3400 K) and exhibited a monotonic increase with operating frequency. Both plasmas produced complex background structure due to excitation of molecular impurities. Significant was the presence of carbon-containing molecules (CN, C2) in the Ar plasma as a result of its enhanced sputtering capabilities. Analyte sensitivity increased with frequency, but detection limits were frequency independent. Sensitivities (peak height and area) for Ag, Cu, Mn, Pb, Ni, and Fe were consistently greater in the Ar plasma.

Communications. Furnace atomisation plasma emission spectrometry (FAPES)

The development and initial evaluation of an atmospheric pressure helium radiofrequency plasma excitation source, established in a graphite furnace, are discussed for use in atomic emission spectrometry.

Impact of bias voltage on furnace atomization plasma emission spectrometry performance

Abstract The effects of an applied d.c. bias potential on the analytical response from a furnace atomization plasma emission spectrometry (FAPES) source operating with a 50 W He plasma were investigated. Enhancements in absolute sensitivity and detection limits for B, Cd, Pb, Ni, Fe, S, Pt and Se ranged from 2–10-fold as compared to the usual “free running” self-bias situation and response from all species was enhanced as the applied bias was made more negative. Reflected power increases up to 35 W exert little effect on the excitation conditions within the plasma. The excitation temperature of the He support gas as well as that of Fe introduced as a thermometric species indicated that, while the temperature of the former varied by up to 700 K over the course of an atomization transient, that of Fe remained relatively stable. Bias control reduced the fluctuation in the He temperature to under 400 K.

Determination of copper, iron, manganese and zinc in river and estuarine water by atom trapping-flame atomic absorption spectrometry

SummaryA simple method is described for the atomic absorption (AA) determination of Cu, Fe, Mn and Zn in river and estuarine water using two atom trapping techniques: a water-cooled dual silica tube and a commercially available double-slotted quartz tube mounted in an air-acetylene flame. Rapid, accurate analyses can be achieved using continuous aspiration. The concentration detection limits were 0.9, 1.5 and 0.3 ng ml−1 for Cu, Mn and Zn, respectively, using a 2 min in situ preconcentration time with the dual silica tube atom trap and 4.0, 12.1, 2.0 and 1.2 ng ml−1 for Cu, Fe, Mn and Zn, respectively, using the double-slotted quartz tube. The relative standard deviations are of the order of 2.9–6.9% for both techniques. The accuracy was assessed by analyses of NRCC SLRS-2 riverine and SLEW-1 estuarine water reference materials. Basic performance characteristics are also given for Ag, Bi, Cd, In, Pb and Tl using the dual silica tube atom trap.

Aerosol Transport Interface for Electrothermal Vaporization-Microwave-Induced Plasma Emission Spectrometry

Electrothermal vaporization (ETV) devices have proven to be useful for introduction of microamounts of solid and liquid analyte into the inductively coupled plasma (ICP), microwave-induced plasma (MIP), and direct-current plasma (DCP) for multielement analyses. Several applications have recently been reported. Trace element analyte characterization studies with ETV-ICP/ MIP/DCP systems inevitably involve the application of a specialized sample introduction configuration. Most introduction schemes rely on formation of an aerosol of the analyte to introduce gaseous samples in a discrete mode. In general, such a system consists of the electro-thermal vaporizer, aerosol transport interface, and plasma emission source (ICP, MIP, or DCP). Ideally, these devices should be simple and efficient, introduce reproducible amounts of analyte without losses, and produce no memory effects. In addition, the aerosol from the graphite furnace should be introduced directly into the plasma without any intervening tubing or connectors. In this way analyte loss, peak broadening, and tailing are minimized, as the analytes are detected immediately upon leaving the graphite furnace. In practice, however, this is not usually feasible, and the graphite furnace is connected to the plasma by means of a short (as possible) length of tubing.

Photo- and thermo-chemical vapor generation of mercury

Photochemical vapor generation of both inorganic and methylmercury species can be achieved with equal efficiency when a sample reaction medium containing 2–10% formic acid is irradiated by low power (0.3 mW) deep UV LED sources with output in the range 245–260 nm. Whereas pseudo first order kinetics is evident for reduction of methylmercury, inorganic mercury does not conform to either first or second order models and the overall reaction rate is proportional to the concentration of formic acid but independent of that of mercury. Noteworthy, is that at room temperature, no reduction of either mercury species is achieved when radiation from 360 nm LEDs is used. A thermal reduction system operating at nominally 85 °C can also be used to reduce both mercury species in a 2% formic acid medium with the initial stages of the reaction being dominated by a first order kinetic process that is approximately 7-fold slower for methylmercury. Despite this disparity in reaction rates, direct speciation is not possible. Using a 10 cm quartz tube cell for cold vapor AAS measurement, a limit of detection of 0.68 ng absolute was achieved for mercury using a 9 min irradiation time with the deep UV LED sources. Precision of replicate measurement was 2.4% RSD for a sampled volume of 480 μl of a 200 ng ml−1 solution of Hg2+ (96 ng absolute) in 2% formic acid. The efficacy of the low power deep UV LED photoreactor was demonstrated by quantitation of total mercury in certified reference materials PACS-2 (marine sediment) and DOLT-4 (fish liver tissue) using the method of additions to compensate for matrix interferences.

Determination of cadmium and lead in sediment and biota by furnace atomisation plasma emission spectrometry

Trace concentrations of cadmium and lead have been determined in dissolved samples of National Research Council of Canada Marine Certified Reference Materials BCSS 1 Coastal Marine Sediment, DORM 1 Dogfish Muscle and TORT 1 Lobster Hepatopancreas by furnace atomisation plasma emission spectrometry. No spectral interferences were evident at either the Cd 228.8- or Pb 217.0-nm lines. Matrix interferences were effectively compensated for by the method of additions, leading to good agreement between the analytical results and the certified values. Estimated procedural detection limits for the determination of Cd and Pb in BCSS 1 are 68 ng g–1 and 3.1 µg g–1, respectively, for an integrated signal response.

Figures of merit for two-step furnace atomization plasma emission spectrometry

A furnace atomization plasma emission spectrometry (FAPES) system was assembled using a two-step graphite furnace which consisted of a spatially isothermal tube positioned at the top of a cup. It was possible to ignite and stabilize an He 50 W r.f. plasma, tuned for a reflected power of less than 5 W, inside the tube, at temperatures of 2500–2600 K and subsequently heat the cup to vaporize the sample. Detection limits for Cr and Al were 298 and 30 pg, respectively. Sensitivities and detection limits for Pb, Cd and Sn were comparable to previously published values using a Massmann-type FAPES system employing a platform and Pd modifier.