Flameless Atomic Absorption Determination of Cobalt, Nickel, and Copper-A Comparison of Tantalum and Molybdenum Evaporation Surfaces' N. S. Mclntyre, M. G. Cook, and D. G. Boase Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment, Pina wa, Manitoba, ROE 1L0, Canada
Molybdenum and tantalum evaporation filaments have been investigated for their suitability in determining nanogram quantities of cobalt, nickel, and copper by flameless atomic absorption spectrophotometry. Tantalum filament surfaces interact with these elements during evaporation making the determination of cobalt and nickel very difficult and lowering the precision of the copper determination. Molybdenum filaments, on the other hand, show no sign of interaction with these elements and give very reproducible results with high absolute sensitivities (5-30 pg). The presence of any oxide or nitride on the evaporation surface results in marked interelemental interference effects. When very clean filaments are used, however, interference effects are significantly lower than those observed for graphite surfaces. An increase in filament temperature results in reduced interelemental interference and improved precision.
Flameless atomization devices of various designs have extended the absolute sensitivity of atomic absorption spectrophotometry to the nanogram level for many elements. Following the earlier design of the King spectroscopic furnace, both L'vov ( I ) and Massman ( 2 ) designed a form of atomizer which is a resistively heated graphite cylinder of 1-cm diameter placed in the path of the interrogating radiation. Another type of atomizer is the graphite filament design developed by West and Williams ( 3 ) .Because of lower thermal inertia and a more open structure, the atom residence time above the graphite filament surface is often an order of magnitude lower than in the graphite cylinder. More recently, atomizer systems employing metal evaporation filaments have been described and appear to have some important advantages. Background emission from a metal filament in the 200- to 350-nm spectral region is lower than that for a graphite surface at the same temperature. Moreover, metal surfaces often can be prepared and maintained in a nonreactive state that is difficult to achieve with a carbon surface of any form. Several investigators (4-6) have studied tantalum filaments for the determination of a number of elements. Tungsten ( 7 ) and platinum (8) filaments have also been investigated to a lesser extent. Corrosion studies in this laboratory frequently require the determination of nanogram quantities of the transition AECL Declassification No. 8274. B. V. L'vov. Spectrocbirn. Acta, 17, 761 (1961). H. Massmann, Spectrocbirn. Acta, PartB, 23, 215 (1968). T. S. West and X. K. Williams, Anal. Cbirn. Acta., 45, 27 (1969). H. M. Donega and T. E. Burgess, Anal. Chern., 42, 1521 (1970). J. Y. Hwang, C. J. Mokeler, and P. A. Ullucci, Anal. Cbern., 44, 2018
(1) (2) (3) (4) (5)
(1972).
(6)T. Takeuchi. M. Yanigisawa, and M. Suzuki, Taalanta, 19, 465 (1972). (7) J. E. Cantle and T. S. West, Talanta,20, 459 (1973). (8) S. R . Goode. A. Montaser, and S . R . Crouch, Appl. Spectrosc., 27, 355 (1973).
elements copper, nickel, and cobalt in samples where higher concentrations of other ions are present. In this work, the first effective use of a molybdenum filament atomizer is described for the determination of these elements. In comparison with tantalum filament surfaces, molybdenum is considerably more inert and is thus more suitable for the determination of copper, nickel, and cobalt. The effects of filament temperature, surface impurities, and the presence of various foreign ions have been investigated for both molybdenum and tantalum surfaces.
EXPERIMENTAL The experimental configuration used is shown in Figure 1. An 1L-355 flameless sampler chamber and power supply are used in conjunction with a 0.25-m Techtron AA-4 monochromator. A small dedicated computer system was developed to record and process the transient elemental absorption signals. The unmodulated radiation from a hollow cathode lamp is focussed to form a beam of
