Alexander I. Yuzefovsky

Determination of ultra-trace amounts of cobalt in ocean water by laser-excited atomic fluorescence spectrometry in a graphite electrothermal atomizer with semi on-line flow injection preconcentration

A method has been developed for the determination of trace and ultra-trace amounts of cobalt in sea-water. Samples of CASS-2 Nearshore Seawater and NASS-4 Open Ocean Water reference materials from the National Research Council of Canada were employed. Laser-excited atomic fluorescence spectrometry in an electrothermal atomizer (ET-LEAFS) was used, and integrated with semi on-line flow injection microcolumn preconcentration. For cobalt, the effects of pH on the preconcentration efficiency, the concentration of the chelating agent and the distribution of cobalt in the ethanol eluate were studied. A bonded silica, with octadecyl functional groups (C18) in a 10 µl column, was employed for preconcentration of cobalt in ocean water. Ocean water volumes of 0.40 and 1.00 ml were required for the determination of cobalt in CASS-2 and NASS-4, respectively. These volumes were almost two orders of magnitude smaller than those required by inductively coupled plasma mass spectrometry and some other competitive techniques. The preconcentration factors were 5- and 12.5-fold for CASS-2 and NASS-4, respectively. The detection limits (3s), based on 12.5-fold preconcentration, were 0.08 and 1.0 ng l–1 for cobalt in aqueous standard solutions and in Ocean Water Reference Materials, respectively. Results for the determination of cobalt in CASS-2 and NASS-4 showed that there were no significant differences between the certified values and the measured values, based on Students t-test at the 95% confidence level. The relative standard deviations for the determinations of the concentrations of cobalt in CASS-2 and NASS-4 were 9 and 13%, respectively.

Electrothermal atomizer laser-excited atomic fluorescence spectrometry for the determination of phosphorus in polymers by direct solid analysis and dissolution

Electrothermal atomizer laser-excited atomic fluorescence spectrometry (ETA-LEAFS) with direct solid analysis was used to measure phosphorus in polymers that consisted mainly of poly(ethylene terephthalate). The ETA-LEAFS detection limit for phosphorus was 8 pg, and the linear dynamic range extended over approximately five orders of magnitude. Electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used to validate quantitative results obtained. A novel dissolution method that utilized trifluoroacetic acid and toluene was used for validation purposes. Of the three techniques investigated, only ETA-LEAFS, with either direct solid analysis or dissolution, could measure the phosphorus content of all the samples over the range 2–3000 µg g–1; ETAAS and ICP-AES were limited by a relatively poor linear dynamic range and/or poor detection limit. The relative standard deviation for the ETA-LEAFS analyses by dissolution and direct solid analysis was in the range 5–11% and 11–12%, respectively. A general comparison was made between the use of ETA-LEAFS and alternative techniques for the direct solid analysis of polymers.

Stray light effects in Zeeman atomic absorption spectrometry

Abstract A transverse Zeeman atomic absorption spectrometer has been modeled using a polychromatic, optical calculus simulation software program. The models were found to be realistic and greatly facilitated the study of the effects of various Zeeman spectrometer parameters and their interactions. The behavior of the Zeeman spectrometer calibration curves, in the presence of three different types of stray light, was modeled. From the initial results, it seems most likely that the major stray light source in real Zeeman experiments is due to polychromaticity of the light source, even when the source profile is relatively narrow in spectral bandwidth.

Role of barium chemical modifier in the determination of fluoride by laser-excited molecular fluorescence of magnesium fluoride in a graphite tube furnace

Some improvement in the determination of fluorine in urine and tap water by use of laser-exicted molecular fluorescence spectrometry of magnesium monofluoride in a graphite tube furnace has previously been reported. The use of barium as a chemical modifier increased the size of the signal by a factor of 100. The work reported in the present paper was carried out in an attempt to elucidate the mechanism of the enhancement of the magnesium fluoride fluorescence by barium, and to explain some other experimental characteristics of the method, such as the vaporization temperature, which was lower at 1800 °C than the 2400–2700 °C reported by other workers. The mechanism of formation of gaseous magnesium fluoride molecules from sodium fluoride and magnesium nitrate solutions in a graphite tube furnace during atomic absorption measurements was investigated with and without the presence of barium. It was shown that, without chemical modification, the formation of magnesium fluoride in the gaseous phase proceeded mainly via interaction between magnesium difluoride molecules and excess of free magnesium atoms [Mg(g)+ MgF2(g)→ 2MgF(g)]. The efficiency of this process was fairly low, primarily because of the difference between the vaporization temperatures of the reacting species (1400 °C for magnesium difluoride and 1800 °C for magnesium vaporized as magnesium oxide). The presence of barium changed the mechanism of formation of magnesium fluoride. It was calculated that the formation of barium difluoride, rather than magnesium difluoride, was thermodynamically preferable in the first step of the mechanism. Experimental data indicated that the formation of magnesium fluoride then proceeded with higher efficiency than without barium because the reaction Mg(g)+ F(g)→ MgF(g) followed the appearance of magnesium from magnesium oxide, and fluorine from barium difluoride at coincidental temperatures in the range 1700–1900 °C.