8.2.2. Interferences and Reproducibility
...One major challenge when analyzing masonry samples is the presence of
carbonate. Concrete, mortar and plaster samples that are several decades old
are all carbonated to a high degree, hence contain major quantities of car-
bonates mainly in the form of calcium carbonate (CaCO3). Meeussen/
Temminghof et al. (1989) have determined the
false positives caused by car-
bonate in liquid solutions of 0.1 mg of cyanide per liter of water as listed in
Table 26.
Considering that masonry samples can easily contain several thousand mil-
ligrams of carbonate per liter – for instance, apart from its sand portion, lime
plaster consists basically only of CaCO3 – cyanide values in the range of 1 mg
per kg sample material and lower may reflect to a considerable degree the
samples’ carbonate rather than cyanide content. Since the photometric method
used by Meeussen/Temminghof et al. is not necessarily identical to those used
by the laboratories dealt with here, however, those values should be taken
only as a caveat that large quantities of carbonate yield false positive near the
detection limit, rendering them unreliable in addition to the problems involved
in general when testing solid samples, as discussed above.
To prove this point, Leuchter’s laboratory re-analyzed two low-level sam-
ples and made a spike analysis for a third. I had four of my samples re-
analyzed by a different laboratory. The results are given in Table 27.
