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Standardization
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Nixon et al. (41 ) used a resistively heated tantalum filament confined under a quartz dome. Vaporized sam ple flows directly from the top of the dome into the sample introduction or ifice of the plasma. Although t h i s de vice was used only for liquids, prelimi nary studies suggest its applicability to solid samples. Grime and Vickers (42) used this approach for sample in troduction into flames for flame emis sion. Recently Gunn et al. (43) vaporized samples from a resistively heated graphite rod enclosed under a glass dome. T h e device was applicable to Ag, As, Au, Be, Cd, Ga, Hg, In, Li, Mn, P, P b , Re, Sb, Ti and Zn. Poor detec tion limits were obtained for carbideforming elements, and with this prob lem in mind Kirkbright and Snook (44) and Kirkbright (45) employed a 0.1% trifluoromethane (freon 23) in argon mixture. Formation of volatile fluorides extended the method to B, Zr, Mo, W and Cr. Detection limit im provements compared to argon alone were one to two orders of magnitude. With equipment similar to Gunn et al. (43), Hull and Horlick (46) deter mined Ca, Ag, Mg, P b , Cu, Zn, Ga and Mn. Signal appeared approximately 1 s after the atomize cycle of the furnace was initiated. High levels of Na cause a spacial shift in emission b u t the in tegrated intensity is not affected. In a commercial offering (47) solids are vaporized in a capillary arc. T h e aerosol thus produced is swept in an argon stream into the inductively cou pled plasma. This approach has been utilized for conducting samples only. A high voltage spark was used by H u m a n et al. (48) to produce particles from solid conducting materials. T h e particles were transported to the plas ma in a gas fed through the spark chamber. Copper was analyzed in alu minum alloys, iron and brass. T h e use of this technique for injection of solids into flames for AAS and AFS analysis was also discussed.
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962 A · ANALYTICAL CHEMISTRY, VOL. 52, NO. 8, JULY 1980
In most cases, whether it be by AAS, AFS or AES, when solids are an alyzed directly it is necessary to em ploy a standard t h a t is similar in com position to the samples. This reflects the strong matrix dependency of the signal in most of the approaches. Generally, the devices discussed under the heading of "hybrid devices" show reduced matrix dependency. T h e techniques which might be expected to be least matrix dependent are those involving the inductively coupled plasma. It is often difficult to obtain suitable reference samples of a wide range of solid samples. T h u s , as a sub stitute, it may be possible to make up synthetic standards from carefully weighed pure constituents t h a t are
