Atomic systems research background

Sensitivity is assessed by comparing signal level and stability of the background with analyte response. In early ICP/MS instruments, response was on the order of 106 ion counts/s per part-per-million (ug/mL) of analyte in a solution introduced at a flow rate of 1 mL/min. This is an analyte introduction rate of 1 ug/min, or 1014 atoms/s for the analyte 100Mo. The overall efficiency is thus 10 8 given 106 counts/s vs. 1014 atoms/s from the sample. Research and development has led to efficiencies that have steadily increased over the years. State-of-the-art instruments and high efficiency sample introduction systems can now achieve 10 3 (0.1 percent) overall efficiency in terms of counts detected per atom in the sample. Champion efficiencies as large as 0.5 percent have been reported (Rehkamper et al., 2001). For comparison, TIMS champion efficiencies are 1 and 5 percent, for uranium and plutonium, respectively. 

Schlemmer et al. [124] continued this research using HR-CS AAS, where the nature of the background absorption becomes apparent, as shown in Figure 8.50. It is quite obvious from the structure of the peak that the interference is not due to an atomic line, but to some molecular absorption, although the kind of molecule that causes the absorption is yet unknown. It also becomes clear that part of the problems observed in LS AAS is the rapid change of the absorbance with time, which is difficult to follow with sequential correction systems. 

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