EFFICIENCY AND EVALUATION - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 404

Figure6.8. Relative detection limits of INAA, TXRF, ICP-MS, and ET-AAS applied to trace
analysis of aqueous solutions or their residues after evaporation. A 50 μ l specimen was used for
TXRF and ET-AAS; 3 ml was needed for INAA and ICP-MS. The individual values should be
considered approximate at best. Data from Ref. [84], reproduced with permission. Copyright
1993, Elsevier.
In contrast to INAA, TXRF and ICP-MS are well suited for liquids or
solutions. Solids first need to be digested or at least dissolved as a suspension.
As a result, losses and contaminations can occur. Furthermore, a limitation of
the dissolved portion, that is, a low salt concentration, has to be observed for
both ICP-MS and TXRF. Highly concentrated acids or bases must be diluted
only for ICP-MS but can be directly analyzed by TXRF. No such restrictions
exist for INAA. The total sample volume applied for analysis is consumed by
ICP-MS, whereas TXRF and INAA are nonconsumptive.
Total reflection XRF and INAA permit detection on the low-pg level; ICP-
MS has detection limits that can even be lower by one or two orders of
magnitude. Limitations exist for certain sets of elements, which are different for
the three methods. While TXRF is limited in the detection of light elements
with Z < 13 and less effective for some transition elements, ICP-MS is ham-
pered in the determination of some elements introduced by air, for example,
nitrogen and oxygen. For some other elements like H, F, P, and S, the
ionization probability in the plasma is rather low. A determination of the
halogens chlorine and bromine in liquid samples is effective for TXRF;
however, it is difficult for ICP-OES and ICP-MS [91].