Richard L. Irwin

Determination of Thallium, Manganese, and Lead in Food and Agricultural Standard Reference Materials by Electrothermal Atomizer Laser-Excited Atomic Fluorescence and Atomic Absorption Spectrometry with Slurry Sampling

Electrothermal atomizer laser-excited atomic fluorescence spectrometry (ETA LEAFS) and electrothermal atomic absorption spectrometry (ETA AAS) have been compared for the determination of three elements in National Institute of Standards and Technology food and agricultural standard reference materials with dissolved and slurried samples. Advantages of slurry sampling include reduced sample preparation and a reduced risk of contamination. ETA LEAFS is an extremely sensitive technique, with detection limits one to four orders of magnitude more sensitive than ETA AAS. Using the front-surface illumination approach, this paper reports the first application of a modern, unmodified graphite tube furnace for the determination of manganese, thallium, and lead in biological materials by ETA LEAFS. Thallium was determined by ETA LEAFS at levels one to two orders of magnitude below the ETA AAS detection limit. The determinations done by ETA LEAFS with the use of either dissolved or slurry sampling agreed well with the certified values, with typical analytical RSDs between 3 and 10%. These precisions were similar to the precisions of the ETA AAS measurements. For ETA AAS, the sizes of the background signals reported in the literature are often about the same order of magnitude as the analytical signal. In this work, the sizes of the background signals for ETA LEAFS were shown to be negligible relative to the fluorescence signals for most samples investigated. The relatively small size for the ETA LEAFS background signals, when compared to ETA AAS background signals, indicates that background correction errors are less likely, and that stringent specifications might be unnecessary for ETA LEAFS background correction instrumentation.

Direct solid sampling of nickel based alloys by graphite furnace atomic absorption spectrometry with aqueous calibration

Abstract The direct analysis of solid nickel based alloy samples was investigated using graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction and a Perkin-Elmer solid sampling cup accessory. Advantages of direct solid sampling include high sensitivity and reduced risk of sample contamination since no dissolution step is used. Using aqueous standards and STPF technology with Zeeman background correction, it has proved possible to analyze small chips of nickel based alloy directly. High temperature alloy standard reference materials (SRMs) were accurately analyzed for low and sub ppm concentrations of the trace metals thallium, bismuth, tellurium, selenium and lead in the alloys. Analyses were done on single alloy chips weighing between 0.5 and 4 mg with typical analytical RSDs of 6–14%.

Transverse Zeeman background correction for graphite furnace laser excited atomic fluorescence spectrometry: determination of lead and cobalt in standard reference materials

Abstract Transverse Zeeman background correction was applied, for the first time, to Laser Excited Atomic Fluorescence in an Electrothermal Atomizer (ETA-LEAFS), and compared to Longitudinal Zeeman background corrected ETA-LEAFS. The system used for this work was a modified Perkin-Elmer Zeeman/5100 furnace/magnet assembly, designed to give a higher magnetic field than the standard commercial unit. Zeeman sigma component energy level splittings were determined for both lead and cobalt by measurement of the atomic fluorescence spectral profile, with magnetic “field on”, as a function of laser wavelength. The splittings were 0.0055 nm and 0.0060 nm for lead and cobalt, respectively. The detection limits for lead and cobalt were 4 and 500 fg, respectively, which were within a factor of two of those without background correction. The shape of the calibration curve, and the linear dynamic range of six to seven orders of magnitude, were not affected by Zeeman background correction. The precision for Zeeman ETA-LEAFS (ZETA-LEAFS) was determined to be 5% for aqueous solutions. Lead and cobalt were determined in National Institute of Standards and Technology (NIST) standard reference materials. Lead was accurately determined in slurried samples of estuarine sediment, coal fly ash and citrus leaves by simple aqueous calibration, with precisions in the 6–14% range. Cobalt was determined in coal fly ash and estuarine sediment by the use of dissolved sampling, and palladium matrix modification, with sample precisions of 5–7%. Cobalt could not be determined accurately by use of slurried samples due to sample matrix interferences. Transverse Zeeman background correction was shown to correct for ETA black body radiation, and backgrounds caused by the addition of 20 μg of AlCl3 to cobalt aqueous standards.

Determination of fluorine in urine and tap water by laser-excited molecular fluorescence spectrometry in a graphite tube furnace with front-surface illumination

Calculations of the coherent production of free pairs and of pair production with electron capture from ultrarelativistic ion-ion collisions are discussed. Theory and experiment are contrasted, with some conjectures on the possibility of new phenomena. 29 refs., 5 figs., 1 tab.

Determination of thallium and lead in nickel-based alloys by direct solid sampling with graphite furnace laser-excited atomic fluorescence

The direct analysis of solid nickel-based alloys was investigated using laser-excited atomic fluorescence spectrometry with an electrothermal atomiser (ETA-LEAFS) and a Perkin-Elmer cup solid sampling accessory. Advantages of direct solid sampling include high sensitivity and reduced risk of sample contamination as no dissolution step is used. Using the front-surface illumination approach for ETA-LEAFS, it has proved possible to apply modern graphite furnace solid sampling technology directly to LEAFS. The advantages of ETA-LEAFS include a long linear dynamic range (5–7 orders of magnitude) and limits of detection that can be 1–4 orders of magnitude better than electrothermal atomic absorption spectrometry (ETAAS). High temperature nickel-based alloy standard reference materials were accurately analysed for low and sub-µg g–1 concentrations of the trace metals thallium and lead, using aqueous calibration. These analyses were carried out on single alloy chips weighing between 0.5 and 2 mg with typical analytical relative standard deviations of 7–20%. The use of an internal gas flow, during atomisation, has been reported in the solid sampling ETAAS literature as a means of reducing the sensitivity of the ETAAS method, a necessity due to the short linear dynamic range of ETAAS. The long linear dynamic range of LEAFS allowed the elimination of the use of an internal gas flow through the furnace for the determination of lead. The analyte backgrounds for thallium and lead in nickel-based alloy solid samples using ETA-LEAFS and ETAAS were compared. The analyte backgrounds for solid sampling by ETA-LEAFS were significantly lower than those for solid sampling by ETAAS.

Probe atomization for laser enhanced ionization in a graphite tube furnace

Abstract Reported here is the first use of laser enhanced ionization (LEI) together with modern furnace technology, for the determination of metals in samples. The experimental arrangement that was used included a pulsed excimer pumped dye laser, a graphite tube furnace, and a graphite probe that was used for both sample introduction and as an electrode. For elements with excitation transitions which promoted the atoms to energy levels within 7000 cm −1 of the ionization limit, such as thallium, indium and lithium, detection limits in the 0.7–2 pg range were obtained. Lead, magnesium and iron, which were excited to levels between 24 000 cm −1 and 31 000 cm −1 from the ionization limit, had detection limits between 10 and 60 pg. The linear dynamic range for each of the elements was between three and four orders of magnitude, and the precision for aqueous standards was between 12 and 16%. Theoretical estimates showed that the final ionization step was collisional ionization, rather than photoionization or radiative ionization by furnace black-body emission, for transitions that were less than 15 000 cm −1 from the ionization continuum. However, for transitions that were more than 25 000 cm −1 from the ionization limit, photoionization and collisional ionization both contributed significantly to the LEI signal. Interferences from easily ionized elements and acids were studied, and indium was chosen as an example analyte. Sodium severely depressed the indium LEI signal in a graphite furnace. Nitric acid and sulfuric acid had little effect upon the indium LEI signal, but the signal was suppressed at high concentrations of hydrochloric acid, probably due to the formation of diatomic indium chloride.