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A shadow spectral digital imaging technique (SSDI) with charge coupled device (CCD) camera detection was used to investigate the spatial and temporal distribution of condensation clouds of analyte species generated in a graphite furnace during the atomization of 5–40-μg masses of metals. Complex, non-uniform structures of aerosol species located away from both the graphite tube axis and walls are prevalent. Species giving rise to observed signals are likely clusters of metals in the case of Ag, Au and Pd, and oxide aerosols for elements such as Al, Ca and Mg. Source scatter often arises during the atomization of relatively large masses of analytes (or during the atomization of real samples containing high concentrations of concomitant matrix species) in the graphite furnace due to such aerosol formation. The SSDI technique is an extremely useful aid to the elucidation of this phenomenon and imaging at several wavelengths using both line and continuum sources in combination with (thermal, incandescent) emission from these structures permits a more complete picture to be developed.

The mechanisms by which the platinum group elements (PGEs) are vaporized in the graphite furnace have been investigated using electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). The results suggest that live of these elements (Ru, Rh, Pd, Ir and Pt) are reduced to their metallic state in the graphite furnace and then vaporized by direct sublimation of the metal. For Os, the vaporization mechanism is different. In the presence of HNO3, two distinct vaporization processes are observed. Volatile oxides of Os are released at low temperatures, but some of this oxide is reduced to relatively involatile Os metal which is then vaporized when the temperature is increased above 2000°C. The addition of TeCl2 chemical modifier was found to have minimal effect on the vaporization mechanism and sensitivity for determination for five of the PGEs. For Os, however, the analytical sensitivity and limit of detection was improved when Te modifier was used in conjunction with a lower vaporization temperature of 1400°C. Optimum conditions for the determination of the PGEs by ETV-ICP-MS are reported, along with their absolute limits of detection; these range from 0.015 pg for Ir to 0.25 pg for Os.

Direct determination of selenium on or in atmospheric particulate matter (APM) has been achieved using an integrated filtration and analysis system developed in our laboratories. The filtration (sampling) and analysis system consists of a porous electrographite plate which is used initially for the purpose of collecting APM and subsequently as a probe in graphite probe furnace atomic absorption spectrometry. Selenium produced a double peak when it was atomized from such an electrographite probe. Palladium nitrate+magnesium nitrate, as a mixed chemical modifier or ascorbic acid as a chemical modifier, eliminated the double peak. The addition of the chemical modifier(s) also removed the unpredictable changes in the peak-height and the peak-area absorbance which occurred from one atomization cycle to the next if the chemical modifier was not used. Precision of 5% RSD (peak-area absorbance) was obtained for an aqueous solution of selenium standard containing 1.25 ng of selenium with palladium nitrate+magnesium nitrate mixed chemical modifier, or ascorbic acid chemical modifer. The characteristic masses and the limits of detection for the aqueous solution of selenium standard with palladium nitrate+magnesium nitrate mixed chemical modifier are 27 and 41 pg (peak-area absorbance), respectively, and with ascorbic acid chemial modifier are 29 and 36 pg, respectively (peak-area absorbance). The results of analysis of the NIST (formerly National Bureau of Standards) Standard Reference Material No. 1648, Urban Particulate Matter, for selenium with palladium nitrate+magnesium nitrate mixed chemical modifier gave a recovery of 92%, and a precision of 10% RSD, and characteristic mass and the limit of detection of 20 and 37 pg, respectively.

The mechanism of aluminium spike formation and dissipation of aluminium atoms in electrothermal atomization absorption spectrometry has been investigated using two different approaches. The first approach employs a graphite electrothermal atomizer coupled to an inductively coupled plasma mass spectrometer (ICP-MS) in a configuration that allows simultaneous measurement of atomic, or molecular, absorption signals and mass spectrometric signals. Aluminium sub-oxide (AlO and Al 2 O) and CO(g) spikes in ICP-MS are correlated with the appearance of both Al atom spikes and Al-containing molecule spikes in absorption spectrometry. The aluminium carbide (AlC 2 ) signal in ICP-MS is not coincident with the appearance of either Al atom spikes or Al-containing molecule spikes in absorption spectrometry. The second approach uses two different imaging systems, i.e. shadow spectral filming (SSF) and shadow spectral digital imaging (SSDI), to provide temporally and spatially resolved absorption profiles of Al atoms and Al-containing molecules during Al spike formation and dissipation. The transverse cross-sectional distribution of Al atoms and of Al-containing molecules in the graphite furnace are complementary to one another for both wall and platform atomization. The highest concentration of Al atoms is near the graphite surface, whereas the highest concentration of Al-containing molecular species is at the centre of the graphite tube. The Al-containing molecules observed in both wall and platform atomization consist of both gaseous Al-molecules and a non-uniformly distributed cloud of finely dispersed Al 2 O 3 (s,1) particles. A mechanism of formation that is consistent with the above experimental observations is presented. It is proposed that Al atom spikes are formed from gaseous Al 2 O precursors and that this reaction is triggered by the formation of a molten, condensed-phase Al 4 C 3 melt.

The mechanism of vaporization of yttrium and the rare earth elements (REEs) has been studied using graphite furnace atomic absorption spectrometry (GFAAS) and inductively-coupled plasma mass spectrometry (ICP-MS). The appearance temperatures for Y and the REEs obtained by GFAAS were generally identical to the appearance temperatures obtained using ETV-ICP-MS. At lower temperatures, Y and the REEs are predominantly vaporized in atomic form or as oxides, while at temperatures above 2500°C, the elements are vaporized as oxides and/or carbides. This accounts for the very high sensitivity of ETV-ICP-MS compared to GFAAS for the determination of these elements. Absolute limits of detection for Y and all of the REEs using ETV-ICP-MS ranged from 0.002 pg for Tm to 0.2 pg for Ce. The use of freon as a chemical modifier was effective in controlling analyte carbide formation and reducing memory effects.

In an attempt to understand the implications of using glow discharge atomizers in atomic absorption spectrometry (AAS), line profiles and kinetic (Doppler) temperatures were measured in commercial hollow cathode lamps and a laboratory-constructed, jet-assisted dc glow discharge atomizer using a high-resolution Bomem Fourier transform spectrometer. Line profiles were measured in the hollow cathode lamps as current was increased from 1 to 30 mA for three resonance atomic lines (Mg 285.21 nm, Al 308.22 nm, and Pb 283.31 nm) having distinctly different hyperfine structure. Although the Al 308.22-nm line was largely unaffected by self-absorption as the lamp current was increased, the Pb 283.31-nm and Mg 285.21-nm lines exhibited pronounced self-absorption broadening at relatively low lamp currents. Kinetic temperatures in the hollow cathode lamps ranged from 320 ± 20 K at low lamp currents to 840 ± 20 K at high currents. With the use of the Ar(I) 415.86-nm line from the argon discharge gas as a thermometric species, kinetic temperatures of 460 ± 20 K to 620 ± 20 K were measured in the glow discharge atomizer under typical analytical operating conditions. These low atomizer gas temperatures imply that the sensitivity and linear dynamic range of analytical calibration curves will be more strongly affected by the lamp current of the primary radiation source and the spectral properties of the analysis line in glow discharge AAS than in flame or furnace AAS, and that operation at low lamp current is essential for optimal analytical performance. The degrees to which the linear dynamic range and the slope of the analytical calibration curve would be affected by the hyperfine structure of the analysis line, the extent of self-absorption in the hollow cathode lamp, the hollow cathode kinetic temperature, and the glow discharge kinetic temperature are considered separately for each atomic line investigated. The kinetic temperatures in the hollow cathode lamps and the glow discharge atomizer were so close that it was possible to obtain absorption line profiles for the three resonance atomic lines in the glow discharge atomizer with the use of hollow cathode lamps as primary radiation sources, i.e., without the necessity of using a continuum source of radiation.

The mechanism of vaporization and atomization of U in a graphite tube electrothermal vaporizer was studied using graphite furnace atomic absorption spectrometry (GFAAS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Graphite furnace AAS studies indicate U atoms are formed at temperatures above 2400°C. Using ETV-ICP-MS, an appearance temperature of 1100°C was obtained indicating that some U vaporizes as U oxide. Although U carbides form at temperatures above 2000°C, ETV-ICP-MS studies show that they do not vaporize until 2600°C. In the temperature range between 2200°C and 2600°C, U atoms in GFAAS are likely formed by thermal dissociation of U oxide, whereas at higher temperatures, U atoms are formed via thermal dissociation of U carbide. The origin of U signal suppression in ETV-ICP-MS by NaCl was also investigated. At temperatures above 2000°C, signal suppression may be caused by the accelerated rate of formation of carbide species while at temperatures below 2000°C, the presence of NaCl may cause intercalation of the U in the graphite layers resulting in partial retention of U during the vaporization step. The use of 0.3% freon-23 (CHF3) mixed with the argon carrier gas was effective in preventing the intercalation of U in graphite and U carbide formation at 2700°C.

Kinetic studies of uptake of metal ions by the Chelex batch technique were made to determine Cd, Cu and Pb speciation in model solutions, a snow sample and a river surface water sample. Inductively-coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS) were used for direct determination of these metals. ICP-MS with the solution nebulization technique minimized contamination and adsorption problems involved in the discrete sampling technique of GFAAS, and hence, gave more precise and accurate results. Also, ICP-MS allowed collection of many more data points than GFAAS and was able to resolve components with similar rates of dissociation, which could not always be resolved by GFAAS with its discrete sampling technique. ICP-MS was therefore preferable to GFAAS for kinetic studies of metal speciation. The kinetic data were analyzed by the iterative deconvolution method. The applicability of the Chelex batch technique to metal speciation was validated by analysis of model solutions containing these metal ions with or without EDTA, NTA and fulvic acid. Use of the Chelex batch technique for Cd, Cu and Pb speciation in snow and river surface water samples revealed a number of kinetically distinguishable components of these metals (as complexes) ranging from one to three, probably present as aquo ions or inorganic complexes in the snow sample, and bound to macromolecules/and or colloidal materials in the river surface water sample.

Modifications to a commercial graphite furnace were made for its use as a sample introduction device with an inductively coupled plasma mass spectrometer (ICPMS) and to allow simultaneous measurement of the atomic absorption and mass spectrometric signals. The effect of the internal Ar carrier gas low, the total Ar carrier gas low, and the vaporization temperature on the integrated ion intensity for Ag was studied. An absolute limit of detection of 0.23 pg was obtained for Ag when vaporization took place from a graphite platform in the presence of sodium chloride chemical modifier. The utility of simultaneously measuring electrothermal atomization atomic absorption (ETAA) and ETV-ICP mass spectrometric signals was demonstrated by investigating the interference of MgCl 2 on the determination of Mn by ETAAS

The results of matrix interference studies using a commercially available cathodic sputtering atomizer for atomic absorption spectrometry are presented. Interferences have been found to result from disruption of the plasma chemistry, chemical reaction with the cathode substrate and changes in the spatial distribution of the solution residue on the cathode surface because of changes in the viscosity and the surface tension of the sample solution. The use of peak-area absorbance and the judicious choice of cathode material has been shown to eliminate some of the observed interferences.

Kinetic studies of chemical speciation by the Chelex-100 batch technique revealed aluminum is present both as an aquo ion and as simple complexes of inorganic ligands in snow, but probably bound to macromolecule complexants and/or colloidal substances in the Rideau River surface water. Two kinetically distinguishable components of aluminum having dissociation rate constants of 1.1 × 10−2, ≤ 5.4 × 10−4 s−1 and three kinetically distinguishable components of aluminum having dissociation rate constants of 5.5 × 10−3, 8.4 × 10−4, ≤6.3 × 10−5 s−1 were observed in snow and river surface water, respectively. One kinetically distinguishable component of zinc having a dissociation rate constant of 9.1 × 10−3 s−1, and three kinetically distinguishable components of zinc having dissociation rate constants of 8.5 × 10−3, 2.5 × 10−3, ≤ 6.0 × 10−5 s−1, were observed in snow and river surface water, respectively. Use of inductively-coupled plasma mass spectrometry (ICP-MS) with the solution nebulizer to follow the kinetics of the uptake of aluminum and zinc by the Chelex resin in the Chelex batch technique allowed collection of many more data points in the same time range than were obtainable by graphite platform furnace atomic absorption spectrometry (GFAAS) with an automatic sampler, with the result that ICP-MS had a greater ability to resolve labile complexes than GFAAS. ICP-MS is therefore preferable to GFAAS for kinetic studies of metal speciation in aqueous samples.

The effects of addition of ascorbic and oxalic acids on the atomic absorption signal for lead are explained by a gas-phase thermodynamic equilibrium model. The gas-phase composition of the graphite furnace was determined as samples containing ascorbic or oxalic acid were pyrolyzed. Hydrogen and carbon monoxide were identified as two of the major pyrolysis products. The amounts of these reducing gases, formed in the atomization cycle, varied with the modifier used, the charring temperature employed, and the condition of the surface of the pyrolytically coated graphite tube. The extent of the shift in the appearance temperature showed correlation with variations in concentrations of hydrogen and carbon monoxide produced by pyrolysis

A scheme for metal speciation has been developed and applied to samples of river water, rain and snow. The scheme combines physical speciation by size using ultrafiltration of the soluble metal species with chemical characterization of the metal species by their dissociation kinetics. The kinetics of metal complex dissociation was studied by anodic stripping voltammetry and by ion exchange at Chelex-100 cation-exchange resin, using both the Chelex column and the Chelex batch technique. These kinetic studies cover a time scale of measurement of ca. 2 ms for anodic stripping voltammetry and up to 6 days for Chelex batch technique, a range of about 8 orders of magnitude. The kinetic results suggest that the copper in the snow sample (pH 3.9) is probably bound to different sites having different bonding energies in polyfunctional complexing agents. Four different copper species having dissociation rate constants of 3.1 X 10 −2 , 1.6 X 10 −3 , 6.2 X 10 −5 , and 8.8 X 10 −6 , s −1 have been observed. All of these species fall in the small size fractions of ultrafiltration. The Al in the Rideau River water sample (pH 8) is probably bound to the different sites in humic materials to yield dissociation rate constants 1.6 X 10 −4 , 1.0 X 10 −6 and −6 s −1 . In the Rideau River water sample, most of the soluble Al species have a large molecular size and are probably associated with humic materials. On the other hand, most of the soluble Al species in the small size fraction are Chelex-nonlabile and are probably Al(OH) − 4 . Use of graphite platform furnace atomic absorption spectrometer allows direct determination of trace metals in freshwaters, to be done routinely, rapidly, and inexpensively.

A charge-coupled device (CCD) camera was used as the detector in an imaging system that was constructed for the investigation of atomizers for atomic absorption spectrometry. The two-dimensional distributions of aluminum atoms and aluminum-containing molecules in an electrothermal atomizer were measured as a function of time. The temporally- and spatially-resolved distributions in the electrothermal atomizer were measured for atomization from both the graphite tube wall and a graphite platform

The interference by sodium chloride with the atomization of manganese in electrothermal atomic absorption spectrometry (ETAAS) has been investigated using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The ETV-ICP-MS technique allows direct observation of the signals of manganese along with matrix components during both the pyrolysis and the atomization step of ETAAS, and thereby allows differentiation between the manganese loss from the furnace during pyrolysis and the loss due to formation of molecular species during atomization. The mechanism of interference by sodium chloride is independent of the pyrolysis temperature. The loss of manganese does not occur during pyrolysis, but is due to vapour-phase interference caused by the formation of manganese chloride during atomization. The addition of ascorbic acid, as a chemical modifier, removes the interference by sodium chloride at all pyrolysis temperatures investigated (450–1100 °C). In ETV-ICP-MS, when the sample of manganese contains only the sodium chloride matrix, the chloride appearance time coincides with that of the manganese suggesting a gas-phase interference mechanism. The addition of ascorbic acid promotes an early release of chloride during the atomization cycle. The chloride appearance temperature is approximately 250 °C lower than that of the manganese (≈1200 °C). In ETAAS this difference in the two temperatures reduces the amount of residual chloride left in the graphite furnace at the manganese appearance time, thereby eliminating the interference of sodium chloride with manganese.

New techniques have been developed for investigating fundamental phenomena occurring during electrothermal vaporization (ETV) as applied to atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). The different nature of electrothermal AAS (ETAAS) and ETV-ICP-MS data make possible the melding of information from both techniques in order to differentiate solid-phase and gas-phase chemical reactions leading to vaporization and atomization and elucidate the mechanism of matrix interferences and the chemistry involved in chemical modification. The significance of chemical modification for ETV-ICP-MS is demonstrated and the use of ETV-ICP-MS in assisting ETAAS for rapid method development is shown. The importance of mass transport effects in ETV-ICP-MS is demonstrated, which indicates that knowledge of the physical and chemical form of the analyte and matrix components is important to the practical application of ETV-ICP-MS to chemical analysis. Non-spectroscopic or matrix interferences in ETV-ICP-MS are more severe than in solution nebulization ICP-MS.

The performance characteristics of a laboratory-constructed cathodic sputtering atomizer for atomic absorption spectrometry have been evaluated. The new atomizer allows for the independent control of argon flow rate and pressure, whereas the only cathodic-sputtering atomizer commercially available for atomic absorption spectrometry (Atomsource, manufactured by Analyte Corporation) does not. Our results follow the model of consecutive, first-order reactions: where A is the analyte atom that has not yet entered the analysis volume of the atomizer, B is the analyte atom that absorbs and C is the analyte atom that is removed from the analysis volume, and k1, and k2 are first order rate constants. The importance of independent control of argon flow rate and pressure is shown by the increase in the k 1 k 2 ratio for Ag for the new atomizer compared to that for the Atomsource. The peak height sensitivity of the new atomizer is up to a factor of 5 better than that of the Atomsource, which does not allow independent control of argon flow rate and pressure. Also, the value of k2 for the new atomizer has been decreased, the result is a peak area sensitivity for the new atomizer that is 1–2 orders of magnitude better than that of the Atomsource. A parametric evaluation of the new atomizer has shown that most of the improvement in peak area sensitivity results from the increased residence time of the analyte atoms. A comparison of the sensitivity of the new atomizer with the sensitivity of the Atomsource has been made using both peak height and peak area absorbance.

Two methods to determine the order of the atom formation reaction from the absorbance signal profile are proposed. In one method, the first-order assumption, which is often used to develop various Arrhenius-type plots in graphite furnace atomic absorption spectrometry (GFAAS), is graphically verified by plotting log ( A m T m 2 ) vslog , where the subscript m indicates the value of the subscripted term XXX the absorbance maximum. The linearity of this plot verifies the first-order assumption. The other method allows one to determine the order of the atom formation reaction at the maximum of the absorbance signal using the equation, . The order of the atom formation reaction of copper from a pyrolytically coated graphite tube was found to be 0.95 ± 0.04 by the graphical method, and 1.01 ± 0.04 by the method of calculation, indicating that the atomization of copper does indeed follow first-order kinetics.

The performance of a new, laboratory-constructed cathodic sputtering atomizer when used in atomic emission spectrometry and atomic absorption spectrometry has been studied. The atomizer employs a six gas-jet configuration with the gas-jets directed at the cathode surface. The atomizer has been constructed to provide an independent control of the flow rate and the pressure of argon gas in the atomizer since the sensitivity is dependent on both the flow rate and the pressure of the gas. The construction of the atomizer and its associated equipment is described. Studies were made of the atomic emission of copper, the atomic absorption of copper and chromium in steel, and the atomic absorption of nickel in brass, using solid, bulk samples in all cases. The effects of variation in the argon gas flow rate upon the atomic emission and the atomic absorption signals were studied at a constant pressure with either a constant voltage or a constant power. The ground state population within the analysis volume was found to be dependent on the sputtering efficiency and the transport efficiency. The excited state population within the analysis volume was found to be dependent on the transport efficiency and the discharge voltage, the latter determining the electron energy distribution. The postulated mechanism for excitation of copper is by inelastic collision of fast electrons with ground state neutral copper atoms, the number of fast electrons being the limiting species in the excitation mechanism.

In this paper three modes of atomization, the pulsed, the transient, and the steady-state mode of atomization, have been characterized for the Atomsource cathodic sputtering atomizer for atomic absorption spectrometry. The results of our studies on interferences and recoveries by the transient mode of atomization using the Atomsource are also presented

The effects of discharge conditions on the sputtering, spatial distributions and transport patterns of sputtered atoms in a demountable, radiofrequency (r.f.) glow discharge (GD) atomizer, were investigated. Results obtained for sputtering of oxygen-free hard copper indicate that the GD plume is constricted by an increase in the Ar gas pressure and disturbed by Ar gas/vacuum flow. It is shown that the glow is an inhomogeneous medium and that most of the sputtered Cu atoms are localized in the front of the sampling orifice. Independent control of flow rate and pressure of the sputtering gas (Ar) is critical in determining the spatial distribution of analyte atoms within the atomizer chamber. Both the flow rate and the pressure of the Ar gas affect the removal of ground-state atoms from the analysis volume. The plasma location at different discharge parameters was also investigated in this study. The results show that the r.f. GD source is able to sustain a stable plasma which enables the sequential atomic absorption analysis and depth profiling of samples such as metal alloys.

A simplified model for heat transfer based on thermal conduction is used to calculate the radial gas temperature distribution inside a semi-enclosed, commercial graphite tube furnace used for atomic absorption spectrometry. In the absence of a forced convective flow of a purge gas, the gas temperature inside the graphite furnace during its heating is lower than the wall temperature. After the wall temperature has attained a steady-state value, the gas temperature approaches the wall temperature and the radial temperature gradient in the gas decreases. The difference between the wall temperature and the gas temperature depends on the temperature program used, the thermal properties of the purge gas, and the atomizer geometry. The residence time of relatively volatile analyte elements is largely controlled by expulsion when wall atomization at high heating rates and high atomization temperatures are used. Analytical sensitivities are often enhanced by vaporizing the analyte into a gas having an approximately constant temperature.

A new analytical method has been developed for direct analysis of solid samples of airborne particulate matter by a graphite probe collection technique coupled with graphite furnace atomic absorption spectrometry. A porous graphite probe is used as a filter for air particles. The probe is then subjected to atomization by being inserted into a graphite furnace which has been pre-heated to a constant atomization temperature. Some aspects of the method have been tested by recovery studies using NBS Urban Particulate Matter, SR M No. 1648, and found to give recoveries of 91–107% for Pb, Cd, Ni, Cu and Mn. By combining a highly efficient filtering medium with the extremely high relative sensitivity of solid sampling, this method has the potential of monitoring sources of air particulate emission with sufficient temporal and spatial resolution for unequivocal identification of the pollution source (at least on a local scale).

For the analysis of solution residues by cathodic sputtering in a glow discharge by atomic absorption spectrometry using the ATOMSOURCE atomizer, the entry of atoms into and loss of atoms from the analysis volume (defined by the geometry of the beam of radiation from the hollow-cathode lamp) can be described by the consecutive, first-order reactions where A is the analyte atom entering the analysis volume, B is the analyte atom that absorbs, and C is the analyte atom that is lost from the analysis volume, k1 and k2 are first-order rate constants. This model yields the following equation for the concentration of the absorbing atoms at time t, [B]t, where [A]o is the initial concentration of analyte atoms at time t = 0. Absorbance profiles of Ag, Al, Au, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb and V were obtained using the ATOMSOURCE in conjunction with a Perkin-Elmer Atomic Absorption Spectrophotometer, model Zeeman 5000 and the Perkin-Elmer Professional Computer, model 7500. The rate constants k1 and K2 were evaluated from kinetic profiles. The rate constants were then used to calculate theoretical absorbance profiles, which were compared with the experimentally obtained absorbance profiles. The results obtained fit the model well, implying that atoms are sputtered direct (i.e. without significant formation of intermediates) into the vapour phase from the solution residue on the cathode surface.

Atomization of yttrium in tube-type electrothermal atomizers was studied using various atomization surfaces: pyrocoated graphite surface, carbidized graphite surface and tantalum or tungsten metal surfaces. Carbidizing of pyrocoated graphite tubes with other carbide-forming metals (Ta, Zr or La) produces refractory metal-carbide surfaces thereby preventing the carbide-forming yttrium to come in physical contact with the reactive graphite surface. The result is an enhancement in the analytical sensitivity (peak height absorbance) of yttrium. The atomization of Y from a metal surface (Ta or W) gives better analytical sensitivity, lower atomization temperature, and negligible memory effect compared with those from metal-carbidized surfaces.

The predictions of a theoretical model, embodied in a computer program, describing the heating characteristics of the furnace surface and the gas phase of an anisotropic pyrolytic graphite furnace heated by the capacitive discharge technique are compared with the experimental results obtained by optical pyrometry and by two-line atomic absorption spectrometry, respectively. The surface temperature gradient around the circumference of the type 1 furnace and along the optical axis of the type 3 furnace are calculated and compared with the measured temperatures. The weighted-average of the theoretically predicted gas temperature is in reasonable agreement with the effective vapour temperature measured by two-line atomic absorption method. The heating rate of the furnace does not have a significant effect on the temperature distribution of either the furnace surface or the gas phase. The effect of the difference in the temperature distribution of the type 1 and type 3 furnaces on the atomic absorption signals is also discussed.

A theoretical model has been proposed for the transient characteristics of an atomic-absorption pulse generated by atomization from a graphite platform in a pulse-heated graphite-furnace atomic-absorption spectrometer. The model has been used (with the aid of a computer program) to predict the effects of various factors on analyte atom populations as a function of time. The various factors studied were heating rate, initial temperature of the graphite tube wall, platform mass and thickness, and activation energy for the rate-determining step in the reaction sequence leading to atom formation. The results predicted by the model are in reasonable agreement with the experimental results obtained by using lead as the analyte element.

A theoretical model, based on a first-order or a pseudo-first-order consecutive rate process to describe transient characteristics of an atomic absorption pulse generated in a pulse-heated graphite furnace, has been established. The effects of change in the parameters on the shape and height of the atom population-time curves have been studied using a numerical integration method. The model has been tested experimentally, and the experimental results are in reasonably fair agreement with those predicted by the model.

A comparative study of three atomization techniques is presented: tube wall atomization, platform atomization and probe atomization, in graphite furnace atomic absorption spectrometry for direct determination of lead in bovine liver. Also presented is the effect of oxygen ashing on the lead atomic absorption signal and on the background absorption due to the organic matrix of bovine liver. Study of the lead atomic absorption pulses given by the three atomization techniques using a detection system having a short time constant relative to the atomization and the residence time of lead from Bovine Liver, SRM No. 1577, has provided a new insight into the atomization processes involved in the techniques. The importance of isothermal atomization in reducing or eliminating matrix interferences and the role of oxygen gas in the ashing cycle are presented and discussed.

This paper describes a simple and rapid method for direct determination of traces of Cu, Zn, Pb, Co, Fe and Cd in the NBS oyster tissue, SRM No. 1566, by graphite furnace atomic absorption spectrometry. The solid sampling technique has been used and this results in much higher relative sensitivity by avoiding large dilution factors involved in the sample dissolution technique. The solid sampling technique also greatly reduces or eliminates serious risk of introducing contamination and/or loss of analytes involved in sample dissolution. The organic matrix of the oyster tissue is burnt off and removed by using a well-defined selective volatilization technique. Loss of Cd during charring (pyrolysis) stage is prevented by forming a relatively thermally stable compound of cadmium by adding (NH42SO4 solution to the oyster tissue sample. Also, quantitative data are presented on the effectiveness of the platform technique in removing matrix interferences. The platform technique uses an anisotropic pyrolytic graphite platform which is inserted into a commercial graphite tube.

A simple and rapid method is described for the direct determination by graphite-furnace atomic absorption spectrometry (HGA-2100) of traces of molybdenum (O.1–4 ng) in synthetic sea water. It is shown that the salt matrix can be removed completely by selective volatilization at 1700–1850°C, but the original presence of NaCl, Na 2 SO 4 , and KCl causes a considerable decrease in molybdenum absorbance, and MgCl 2 and CaCl 2 a pronounced enhancement. The presence of MgCl 2 prevents the depressive effects. Samples of less than 50 μl can be analyzed directly without using a background corrector, with a precision of

A simplified transient thermal analysis of a graphite furnace and a graphite platform has been developed and embodied in a computer program to allow predictions of the platform temperature as a function of time. Predictions of the model have been compared with the experimental results to establish confidence in the model. The model has been used to determine the effects of various parameters on the temperature history of the plaftform. The effective vapour temperature has been measured by a two-line absorption method using Sn, Ni and Pb as the thermometric species, and the measured temperature has been explained in terms of the spatial and temporal distribution of the concentration of the thermometric species. This study has confirmed that in the platform atomization the vapour temperature is much higher than what relatively volatile elements would experience in the wall atomization, and the vapour temperature remains constant after the wall temperature has become constant. The most significant contribution of the analytical model is to our understanding of the effects of the final and the initial wall temperature and of the wall heating rate on the heating rate and the temperature of the platform and on the analyte atomic absorption pulse. The usefulness of this model lies not only in its considerable predictive power but also in its ability to provide a satisfactory theoretical framework which gives an insight into the working of the platform.

Selenium can be determined in aqueous solution by atomic absorption spectroscopy at 1960, 2040,2063 or 2075 A; the sensitivities for these lines with a Techtron 10-cm air-acetylene burner are in the ratio of 1:9:60:93. When a Beckman tripleburner (air-hydrogen) and a triple-pass optical system are used, the most sensitive1960 A line provides a sensitivity of 0.5 p.p.m. and a detection limit of 1.0 p.p.m. The performence in air-hydrogen and air-acetylene flames is described,and optimum experimental conditions determined.With the Se 1960 A line and a Techtron 10-cm air-acetylene burner, selenium extracted into methyl isobutyl ketone as its diethyldithiocarbamate complex gives a sensitivity of 0.30 p.p.m.,which is a 2.4-fold increase over that found in aqueous solution.

A carbon-rod atomizer (CRA) fitted with a ‘mini-Massmann’ carbon rod was evaluated for routine analysis of petroleum and petroleum products for trace metal content by atomic-absorption spectroscopy. Aspects investigated included sensitivity, detection limit, effect of solvent type, and interferences. The results of analysis of oil samples with this technique were compared with those obtained by other techniques. Metals studied were silver, copper, iron, nickel, and lead. Sensitivity and detection limit values obtained with the CRA were similar to those obtained with the carbon-filament atomizer. Strong ‘solvent effects’ were observed as well as interference by cations. On the basis of this study, design changes for the CRA are suggested, with the object of minimizing ‘solvent effects’ and interferences, increasing the atomization efficiency, and increasing the residence time of the atomic vapour in the optical path of the instrumental system.

The sensitivities of lead in aqueous and organic media by atomic-absorption spectroscopy using lead lines 2170 Å, 2833 A, and 4058 Å, and an oxy-hydrogen or oxy-acetylene flame were studied. When lead in aqueous solution was complexed as K2PbI6 and the complex extracted into methyl isopropyl ketone, a threefold increase in sensitivity relative to the aqueous solution of lead (as lead nitrate) was obtained. Using a 178-mm-long adapter on the top of a Beckman integral aspirator—burner (oxy-hydrogen), a sensitivity (in ppm/1% absorption) of 0.007 and a standard deviation of 0.014 ppm were obtained with a sample containing 0.1 ppm lead. Results obtained with oxy-hydrogen and oxy-acetylene flames have been discussed, and the precision and detection limits indicated. A procedure to determine lead in ppb—ppm level by extracting lead as K2PbI6 in methyl isopropyl ketone has been prescribed.

Zusammenfassung The role of complexing agents and organic solvents in atomic absorption spectroscopy has been investigated and their effect on the sensitivity of determination of metals has been broadly classified under three categories: (1) an enhancement of 2–8-fold—the majority of metals fall under this category; (2) an enhancement of up to approximately 21-fold with metals such as Al and Ti which form refractory compounds that are reducible; (3) a depression of sensitivity in the cases of a few metals which form refractory compounds which do not undergo reduction. An explanation of this enhancement and depression of sensitivity has been suggested.

Studies on sensitivity in atomic absorption spectroscopy of nickel, tin, titanium, zirconium, hafnium, niobium, and tantalum, as metallocenes and as simple salts or oxy-salts, have shown that the metal–oxygen bonded species in solution (as in the case of simple salts or oxy-salts or complexes with ligands having oxygen atom as the donor) contributes to the total amount of metal oxide in flames, and hence, depopulates the ground electronic state of the atom in flames. In the case of the metals which form oxides of high dissociation energy, sensitivity is enhanced if the metals in solution are not bonded to oxygen as in metallocenes or fluoro complexes. The importance of the dissociation equilibrium and the reduction equilibrium in populating the ground electronic state of the atom has been assessed, and an irregular correlation has been established of enhancement in sensitivity with the metal–oxygen dissociation energy.

A new analytical technique has been developed using the capacitive discharge technique (CDT) for heating graphite furnaces in atomic absorption spectrometry (GFAAS). The CDT employs an anisotropic pyrolytic graphite tube atomizer which is heated at very high heating rates (up to 100 K/ms) by capacitive discharge resulting in isothermal atomization at high temperature (up to 3500 K). Since the CDT is relatively free from matrix interferences and the sensitivity is independent of matrix, analytical calibration curves are not required nor used. Analytical results showing ~ 100% recoveries of analytes from simulated and real samples are presented and compared with those obtained using the conventional GFAAS. National Bureau of Standards Standard Reference Materials were analyzed using the constant obtained from pure metal standards in ultrapure water and the CDT gave ~ 100% recoveries. Background correction was not used. This relative freedom from matrix interferences results from a combination of factors: high heating rates and high temperature, isothermal atomization. Heating rates of about 60 K/ms and above are required for 100% recovery of some analytes from saline water samples. The main advantages of the CDT over the conventional GFAAS are relative freedom from matrix interferences and contamination, and freedom from requirements of chemical treatment of samples, analytical calibration curves, and background correction, resulting in shorter analysis time and lower cost per analysis.

A thermodynamic (gas phase) equilibrium model of atomisation has been used to explain the shift of the appearance temperature of the Pb atomic absorption signal to a lower value when ascorbic acid is used as a matrix modifier. Experimental results of the effect of gas-phase composition on the appearance temperature of the Pb atomic absorption signal are presented. The partial pressure of H2 was determined at various temperatures during the ashing and the atomisation cycle. The partial pressure of CO, CO2 and CH4 were found to be very low for the tube wall heating rate of 1.7 K ms–1; CO was found to be present in appreciable amounts for the tube wall heating rate of 1.5 K ms–1. The results are consistent with the hypothesis that H2 and CO released by the pryolysis of ascorbic acid decrease the partial pressure of O2 in the furnace and thereby cause the equilibrium position of the reaction PbO(g)⇌ Pb(g)+½ O2 to shift to the right, favouring production of more Pb(g), which results in a lowering of the appearance temperature of the Pb atomic absorption signal in agreement with the equilibrium model.

Analytical applications of cathodic sputtering in a glow discharge have almost wholly involved producing a steady-state atomic vapour, which suffers from relatively poor sensitivity and limit of detection common to the steady-state mode of atomisation. The formation of atoms in and loss of atoms from an analysis volume (defined by the geometry of the incident radiation from the hollow-cathode lamp) can be described by consecutive, first-order reactions, [graphic omitted], where D is the pre-atomisation species, B is the analyte atom that absorbs, C is the analyte atom that is lost and k1 and k2 are first-order rate constants. For k2≫k1, d[B]/dt= 0 (t is time in seconds) and the system is said to have reached a steady state. At the steady state, [B]=[D]0k1/k2, which makes [B] much less than [D]0, the initial concentration of the analyte atoms. Hence, the steady-state mode of atomisation gives low sensitivity.The objective of transient atomisation is to maximise [B] by making k1≫k2. For k1≫k2, [B]≈[D]0, and [B] then reaches its maximum possible value, giving the maximum absorbance. This paper presents the results of a preliminary study on transient atomisation with an Atomsource, used in conjunction with a Perkin-Elmer Model 5000 atomic absorption spectrometer and a Perkin-Elmer Model 7500 professional computer. Aqueous solutions of salts of Al, Cd, Co, Cu, Fe, Mn, Mo, Ni and V, one element in one solution, were used. The rate constants, k1 and k2, were evaluated from kinetic profiles and yielded k1/k2≫ 1, which satisfied the condition required for making [B]≈[D]0, yielding high peak-height sensitivity and an excellent detection limit for the above elements. Kinetic analysis revealed that the rate constant for atom formation in the early stages of the reaction (after a transition period), attained a much larger value (to be called k3) at later times. This rate constant for atom formation, k3, obtained from later times of atomisation, rather than k1 obtained from earlier times of atomisation, was used (i.e., k3≫k2) as the criterion for the peak-height sensitivity.