D.C. Manning

The Determination of Trace Elements in Natural Waters Using the Stabilized Temperature Platform Furnace

We have developed procedures to determine 12 trace elements, Al, As, Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, and V, in natural water using the stabilized temperature platform furnace. Suitable matrix modifiers were tested. Confirmation of the techniques was obtained by recovery experiments at four different concentration levels. Only simple aqueous standards were required and the method of additions was not used. A simple recovery experiment was satisfactory confirmation of freedom from chemical interferences. The detection limits in the natural waters were less than 1 μg/liter, closer to 0.1 μg/liter for most of the elements. The precision was 10 to 15%. The work did not require clean-room facilities.

Graphite-tube effects on perchloric acid interferences on aluminum and thallium in the stabilized-temperature platform furnace

Abstract The determination of aluminum in the presence of perchloric acid is shown to depend upon the quality of the pyrolytic coating of furnace tubes. With new pyrolytically coated tubes, no interference was found from 0.5 M HClO4 on 0.5 ng Al and no decrease in signal or deterioration of the pyrolytic coating was found after more than 150 firings. Very little interference was found in the determination of thallium in perchloric acid. In both cases the literature reported severe interferences. The determination of thallium and aluminum in perchloric acid appears to be more sensitive to the quality of the pyrolytic graphite coating than any of the materials studied previously here.

Factors influencing the atomization of vanadium in graphite furnace AAS

Abstract We have made the determination of V conform to the requirements of the modern (stabilized temperature) furnace technology where the integrated absorbance (A·s) signals are used to quantitate analyte volatilized into a chamber whose temperature is relatively constant during the period when the analyte peak is measured. Graphite tubes with good pyrolytic coating and fast (maximum power) heating are required. We explored the advantages of specially designed tubes, of a cool-down procedure between the char and atomization steps and of very thin platforms. We found that Mg(NO 3 ) 2 was advantageous as a matrix modifier. With these conditions we found no problems with several matrices reported by earlier workers to be troublesome, for example HNO 3 , phosphate, Fe, Mg and Ca. However metals that form very refractory carbides, such as La, Mo, W and Zr may remain troublesome for V, probably because mixed carbides result which include VC. A group of geological samples was analysed for V. Our recommendation is the use of wall atomization from tubes with good pyrolytic coatings, Mg(NO 3 ) 2 as a matrix modifier and the cool-down procedure to establish a nearly constant temperature along the tube.

Fast analysis with Zeeman graphite furnace AAS

Abstract Stabilized Temperature Platform Furnace (STPF) methods have been adapted and altered to reduce the analytical time to less than 1 min per sample with no loss of analytical precision or accuracy. It is shown that this could be further reduced to about 30 s per sample if certain changes in instrumentation are implemented, especially in the software and firmware that control the autosampler. The sample uptake rate for the autosampler should overlap the cooldown of the tube from the prior determination. Also, the sample should be deposited onto a heated platform. In this work the pyrolysis step and, in most cases, the use of a matrix modifier has been omitted. Since backgrounds were therefore larger, the use of Zeeman correction was usually required, but continuum background correction was not tried. To confirm that these fast analytical methods might be practical, more than 10 standard reference materials were analyzed for several elements including Pb, Cd, Cu, Ni, As and Cr. The paper is not primarily intended to provide routine and reliable methods; it is intended to test the feasibility of these fast methods.

Investigation of aluminum interferences using the stabilized temperature platform furnace

Abstract Al was determined in the stabilized temperature platform furnace with very few interferences. No interferences were found for several metal nitrates, sulfates or phosphates, or for NaCl. The Al absorbance signal was delayed in the presence of MgCl 2 but there was no interference. This led to the use of 50 μg Mg(NO 3 ) 2 as a matrix modifier for Al. There were no interferences for CaCl 2 but it was particularly important to use new pyrolytically coated tubes to avoid “aging” effects. CuCl 2 provided a very persistent interference that was reduced when the Mg(NO 3 ) 2 matrix modifier was used that permitted a char temperature of 1700°C. Perchloric acid interferences were severe with improperly coated graphite tubes but did not exist up to 0.5 M HClO 4 when the new pyrolytically coated tubes were used. A serum Al method was tested briefly and no problems were found. Al was determined in seawater with no influence from the salinity of the sample and less than 0.6 μg/1 Al in seawater could be detected.

The determination of thallium with the stabilized temperature platform furnace and Zeeman background correction

Abstract Palladium, about 5–10 μg as Pd (NO3)2, is confirmed as an effective matrix modifier for Tl. A pyrolysis temperature of 1000°C can be used, which is a much higher temperature than could be used with the previously proposed matrix modifier, H2SO4. The recovery of Tl was quite good in the presence of large amounts of NaCl but was inadequate in the presence of KCl. Abandoning the pyrolysis step and the matrix modifier proved to be convenient for determining Tl in both an NaCl and a KCl matrix. Thallium was fully recovered in these matrices in the presence of about 30μg of either salt, or about 0.15%, assuming a 20μl sample.

Quality-assurance procedures for graphite-furnace atomic-absorption spectrometry.

A procedure is described for quality-control in graphite-furnace atomic-absorption spectrometry. It uses an NBS standard reference material to avoid errors in standard preparation, and very simple instrumental conditions, with no matrix modifier or pyrolysis step. The characteristic mass and the Zeeman ratio are calculated for Ag, Cu, and Cr, and deviations from the expected values for these quantities are correlated with potential instrumental malfunctions.

The determination of manganese by electrothermal atomic absorption spectrometry with a graphite furnace at constant temperature

Abstract Many of the interferences reported earlier for the determination of manganese in a graphite furnace were not found when a modern graphite furnace was used. At high levels of chloride matrix, an interference which was observed in the modern furnace was reduced when manganese was determined under constant temperature conditions. In this work, the sample was introduced on a tungsten wire after the graphite furnace had reached a constant, preset temperature. Drying and ashing were accomplished outside the atomization furnace, reducing contamination from matrix materials.

The graphite probe constant temperature furnace

Abstract A graphite probe, on which the sample is deposited, is thrust into a heated graphite furnace tube, providing a constant temperature furnace environment. By comparison with wall sampling, the graphite probe system provides equal or improved sensitivity and detection limit and considerably less memory effect. Experiments with metals that range from volatile to refractory show that the peak width is the same at the same atomization temperature. A tube was designed that provided a curtain of argon to limit the absorbance path to about 15 mm.

Properties of the cadmium determination with the platform furnace and Zeeman background correction

Abstract Cadmium, previously a difficult determination in inorganic matrices with the graphite furnace, is shown to be easy to determine with the combination of the stabilized temperature platform furnace, appropriate matrix modification and Zeeman background correction. The optimized conditions were suitable for many matrices; seawater and urine were explored in some depth. Natural water samples were analyzed for Cd. The matrix modifier included ammonium phosphate and either Mg(NO3)2 or NaCl. Simple working curves were used. Problems associated with char losses were studied and recovery experiments were shown to expose such problems. The concept of characteristic amount, the mass of analyte that produced a 1 % absorption signal (0.0044 abs), especially using integrated absorbance data, was shown to be a very powerful diagnostic tool for graphite furnace work. The characteristic amount for Cd was 0.35 pg/0.0044 abs-s, and it varied little with variations in experimental conditions. The effect of background signals that were evolved rapidly was to disrupt the Zeeman signal. Guidance is provided in identifying and controlling these problems. The advantage of the Zeeman technique in providing improved detection limits using bright sources was explored.