ance. Another limitation is the inability to modulate the magnetic field at frequen cies > 120 Hz. This becomes a problem if the generation of the background during the atomization cycle results in short lived species on the order of the time between field-on and field-off conditions because the background is either underor overcorrected. Your decision "GFAAS has evolved into a mature tech nique for the determination of ultratrace concentrations of metals in a wide variety of samples," says Rayson. "Use of the plat form and other delayed atomization ap proaches and chemical modifiers allows the analyst to achieve phenomenal limits of detection with a relatively modest capi tal investment. Many of the significant breakthroughs have come because of a better understanding of the fundamental chemical and physical processes occur ring within the atomizer during the dif ferent stages of the heating program. The innovations in commercial instru ments reflect the fundamental knowledge that has been gained, such as the exist ence of thermal gradients within a Massman furnace, which led in part to the de velopment of the transverse-heated fur naces now available on some instruments. The understanding of chemical interac tions that occur within the atomizer now allows the analyst to reasonably predict which chemical modifiers should be used in the determination of specific met als within a particular sample matrix. Al though GFAAS is a mature technique, that does not mean that it is beyond fur ther growth and improvement. There are as yet many unanswered questions and difficult samples left to conquer, such as the direct deposition of slurry samples into the atomizer and direct introduction of solid samples." He adds, "The selection of a GFAA spectrometer for routine analyses should be based on what the instrument will actu ally be required to do. Each of the op tions available provides its own set of limi tations and capabilities. As the offerings of the different manufacturers are evalu ated, the number, types, and variety of samples that will be analyzed must be con sidered, and the best overall configura tion that meets those needs should then be chosen. There is no one configuration that will be all things to all users—there is presently no one instrument that is the 'best' for all metals in all samples." Felicia Wach
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Analytical Chemistry, Vol. 67, No. 1, January 1, 1995 5 5 A
