Page 407 - Tandem Techniques

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Powell et al. [40], developed a sensitive technique, employing an LC/MS tandem instrument, fitted with
an API interface, to determine the speciation and the quantitative assay of Cr(III) and Cr(VI). The API
interface used a direct injection nebulizer, and they demonstrated a sensitivity of 30, 60 and 180 ng/l for
the total chromium, Cr(III) and Cr(VI) respectively. The sample volume injected was 10 µl, and thus
the actual mass sensitivity appears to be 0.3, 0.6, and 1.8 pg of the total chromium, Cr(III) and Cr(VI)
respectively. A diagram of the sampling arrangement is shown in Figure 9.45.

Figure 9.45
Valve Configuration for the Simultaneous
Monitoring of Total and Speciated Chromium
The valves were connected so that the 10 µl sample could either be directed through the LC column,
which would separate the different chromium species, before the eluent passed to the direct inlet
nebulizer, or to a by-pass loop, which would allow the total sample to be passed directly to the
nebulizer. The same procedure was used as described previously,