Bernard Radziuk

Permanent iridium modifier for electrothermal atomic absorption spectrometry

The suitability for chemical modification of a pure metal layer, deposited on the inner surface of a graphite tube by cathodic sputtering of Ir in a low pressure Ar discharge, was investigated. The characteristics of the deposited layer were studied using scanning electron microscopy and compared with those of Ir deposited from solution. The analytical performance of the modifier was assessed in the determination of Cd, Mn, Pb, Se and V. When sufficient Ir was deposited by sputtering, a homogeneous layer covering the entire tube surface was formed which changed only slightly during the entire lifetime of the graphite tube. Thus integrated absorbance remained essentially constant for more than 700 atomizations. The volatile elements Cd, Pb and Se were thermally stabilized in the absence of a matrix to 800, 1200 and 1400 °C, respectively. The rate of atomization for Mn and V was, however, unfavourably delayed in the Ir-coated tubes.

Reduction of Background Absorption in the Measurement of Cadmium, Lead and Selenium in Whole Blood Using Iridium-sputtered Graphite Tubes in Electrothermal Atomic Absorption Spectrometry

The thermal behaviour during pyrolysis and of the vapour phase during atomization for Cd, Pb and Se in acid-digested whole blood using Ir-sputtered tubes is described. The performance of Ir as a permanent modifier was affected unfavourably by the complex matrix compared with conventional modifiers. Background absorption was measured using an atomic absorption spectrometer in addition to a diode-array spectrometer and compared with the background obtained in pyrolytic graphite-coated graphite tubes. Both methods of measurement indicated that the background was much reduced in the Ir-sputtered tubes. The decrease in background absorption improves conditions for the measurement of these elements. Background molecular absorption was also measured as a function of time. Molecular species such as NO were detected in the vapour phase using pyrolytic graphite-coated tubes, whereas CS and CO were detected using Ir-sputtered tubes.

Chemical modification and spectral interferences in selenium determination using Zeeman-effect electrothermal atomic absorption spectrometry

The role of chemical modification was studied with regard not only to thermal stabilization and atomization of selenium but also to the suppression of spectral interferences on Zeeman effect based background correction. Various amounts of palladium and nickel were used as modifiers at a series of pyrolysis and atomization temperatures for the direct determination of selenium and phosphorus in whole blood and urine reference materials. An attempt was made to correlate phosphorus atomization profiles and the occurrence of compensation errors in the determination of selenium. The smallest errors were measured for those conditions under which the atomization efficiency for phosphorus was enhanced or the volatilization of phosphorus-containing species was significantly delayed. Analytical procedures for the spectral interference-free determination of selenium in each of the matrices studied are described.

Palladium nitrate–magnesium nitrate modifier for electrothermal atomic absorption spectrometry. Part 4. Interference of sulfate in the determination of selenium

The possible sources of sulfate interferences in the determination of selenium, even when stabilized temperature platform furnace conditions were used, were investigated using sulfuric acid, sodium sulfate and magnesium sulfate as model compounds. The molecular spectrum of CS was observed when sodium sulfate was volatilized. The most likely mechanism of interference in this instance is an expulsion of the analyte element with the violently volatilized matrix early in the atomization stage. Sulfuric acid and magnesium sulfate decompose at elevated temperatures with the formation of SO3, which was reduced at least in part to SO2 in the graphite tube. The most likely interference mechanism in these instances is the formation of SeO2 in the presence of excess of SO3 and its volatilization during the pyrolysis stage. Addition of barium nitrate to the palladium nitrate–magnesium nitrate modifier reduced the background absorption and also the sulfate interference significantly. In the presence of barium, sulfate is bound at least in part as barium sulfate, which decomposes in the atomization stage. This means that SeO2, if it is formed, is volatilized at temperatures which are high enough for its atomization. The proposed mixed modifier allows an interference-free determination of selenium in mineral waters with high sulfate content.

Gas chromatography coupled with atomic absorption spectrometry — a sensitive instrumentation for mercury speciation

Abstract New instrumentation for the speciation of mercury is described, and is applied to the analysis of natural water samples. The separation of mercury species is effected using gas chromatography of derivatized mercury species on a widebore capillary column. The solvent is vented using a bypass valve and the separated mercury species are pyrolysed on-line at 800°C for production of mercury atoms. These are then detected by atomic absorption spectrometry (AAS) at the 253.7 and 184.9 nm lines simultaneously in a quartz cuvette. The use of the 184.9 nm line provides a more than five-fold increase in sensitivity compared with the conventional 253.7 nm line and an absolute detection limit of 0.5 pg of mercury. The dynamic range of the combined analytical lines provides a linear response over more than three orders of magnitude. A number of organic compounds not containing mercury are also detected following pyrolysis, especially at the 184.9 nm line. These background species must not co-elute at the retention times for methyl- and inorganic mercury, as otherwise a positive interference would result. By maximizing the chromatographic resolution and minimizing the band broadening in the cuvette by use of a make-up gas, the retention times of interest are freed from co-eluting background peaks. The instrumentation has been applied to the determination of ng l−1 concentrations of methyl- and inorganic mercury in Lake Constance, Germany and within the Lake Constance drinking water supply organization, Bodenseewasserversorgung (BWV). The accuracy for the sum of methyl- and inorganic mercury has been assessed by comparison with an independent method for total mercury based on AAS detection implemented at BWV. Relative detection limits using 1 litre water samples and 15 ml injections of the final hexane extract were 0.03 ng l−1 for methylmercury and 0.4 ng l−1 for inorganic mercury based on the 3j criterion.

Evaluation of internal standardisation in electrothermal atomic absorption spectrometry

Significantly improved performance in electrothermal atomic absorption spectrometry is possible using an internal standardisation technique. A Perkin-Elmer SIMAA 6000 simultaneous multielement spectrometer was used to study the correlation between two integrated absorbance signals. The behaviour of Pb (analyte) in different urine, blood and placenta samples was compared to that of Bi or Tl used as the internal standards. All samples were spiked with known amounts of Pb and Bi or Tl. A satisfactory signal correlation (r = 0.94) between the integrated absorbances for spikes of the analyte and internal standard was observed with Bi as the internal standard. After signal correction, the relative standard deviation of the integrated absorbance for Pb spikes reduced from 29 to 7% for urine, from 19 to 2% for blood and from 22 to 4% for placenta. The mean difference between Pb concentration found in analysed samples by the method of additions and using an internal standard was 10%.

Effect of furnace atomization temperatures on simultaneous multielement atomic absorption measurement using a transversely-heated graphite atomizer

The sensitivities and signal-to-noise ratios (SNRs) of five elements (Cd, Pb, Cu, Cr, and V) were characterized for atomization by a commercially available transversely heated graphite atomizer (THGA) as a function of the atomization temperature, with and without a Pd–Mg(NO3)2 matrix modifier, and with a standard furnace and an “end-capped” furnace to restrict diffusional loss of the analyte. These five elements were selected to provide a representative range of atomization temperatures. In general, the sensitivities of Cd, Pb, Cu, and Cr decreased with increasing atomization temperature and the sensitivity of the least volatile element, V, increased with temperature. The most suitable temperature for simultaneous determination of these elements was 2500 °C, as dictated by V. The loss in sensitivity for the atomization of Cd and Pb at 2500 °C was 25 to 35%, considerably less than predicted by mass diffusion. With use of the modifier and ‘endcapped’ THGAs, the temperature dependence of the sensitivity approached that predicted by mass diffusion. With photon shot noise and optimization of the integration interval, the best SNRs for all elements, in the simultaneous multielement mode or in the single element mode, are found at approximately 2500 °C and no compromise is necessary.

Spectrometer system for simultaneous multi-element electrothermal atomic absorption spectrometry using line sources and Zeeman-effect background correction

The design and implementation of a complete instrument system for simultaneous analysis of up to four elements by electrothermal atomic absorption spectrometry is described. The system combines the high throughput per unit spectral bandpass of an echelle optical system with the high quantum efficiency of a custom made solid-state detector. The use of a transversely heated graphite atomizer with integrated platform in a longitudinally oriented magnetic field enables the development of methods for simultaneous multi-element determinations and increases radiation throughput by eliminating the need for a polarizer. Performance characteristics such as optical throughput, spectral resolution and stray light are discussed and correlated with analytical performance using a state of the art single-element atomic absorption spectrometer system as a basis for comparison.

Combination of flow injection hydride generation and sequestration on a graphite tube for the automated determination of antimony in potable and surface waters

A method for the determination of antimony in potable and surface waters has been developed, combining the use of flow injection apparatus for hydride generation with sequestration of antimony on a graphite tube, followed directly by atomization and measurement of atomic absorption. The entire measurement procedure and the acquisition of data were under microcomputer control, permitting fully automatic operation and improving measurement precision. Sample volumes of up to 500 µl can be manipulated using a sample loop and injection valve, whereas for larger volumes a continuous flow technique has to be used. A study of recovery demonstrated that more than 90% of the antimony contained in sample volumes of up to 5 ml was retained on the surface of an uncoated electrographite tube. Statistical evaluation of calibration data yielded a limit of determination of 20 pg and a limit of detection of 15 pg. This means that in a sample of 5 ml a limit of determination of 5 ng l–1 was obtained, making the reliable determination of antimony at concentrations found in some surface waters possible. The method was applied to the depth profiling of total and dissolved antimony in lake water. In Lake Constance a maximum particle-bound concentration of 25 ng l–1 was measured.

Use of a Segmented Array Charge Coupled Device Detector forContinuum Source Atomic Absorption Spectrometry With Graphite FurnaceAtomization

A commercially available echelle spectrometer with a segmented array charge coupled detector (SCD) was used with a xenon arc lamp and graphite furnace atomizer for continuum source atomic absorption spectrometry (CS-AAS). Approximately 67% of the spectral wavelengths corresponding to the resonance transitions used for routine AAS determinations were available on the SCD. As many as eight elements were determined simultaneously with a read frequency of 50 Hz for each array. The high luminosity of the echelle and the high quantum efficiency SCD provided photoelectron levels that ranged from equivalent to 7 times higher than those previously measured by CS-AAS using a linear photodiode array (LPDA) detector. The low read noise of the SCD resulted in the absorbance measurements being limited by the photon shot noise of the continuum source. Detection limits were obtained that ranged from equivalent to a factor of 3 better than those previously obtained for CS-AAS and from a factor of 2 worse to a factor of 10 better than those for conventional, line source AAS. Sensitivities, as determined by intrinsic mass (mass necessary for an absorbance of 0.0044 pm s), were similar to those measured previously with an LPDA. The high resolution of the echelle allowed detailed inspection of the spectra surrounding the wavelength of the elements determined. Data were displayed using contour absorbance plots. Molecular peaks were observed within the spectral window of the sub-arrays for As (193.7 nm) and Se (196.0 nm). These peaks were spectrally and temporally resolved from the analyte peaks and disappeared in the presence of a Pd chemical modifier. A low sensitivity Pd line was identified that was 15 pm from the Se line. The Pd and Se peaks were resolved using a spectral bandwidth of 3 pm per pixel.