Chemistry Reference
In-Depth Information
16.3 Criteria for New Fluorimetric and Colorimetric
Methods to Quantify Trace Amounts of
Palladium
The following criteria are important for the development of fluorimetric or
colorimetric methods to quantify trace palladium in synthetic APIs:
1. The method must be selective for palladium - If a palladium-catalyzed
reaction has been performed, the remaining trace metal is most likely
palladium, although other metals may be present. Therefore, spec-
tacular selectivity for palladium is not necessary, but other commonly
found metals such as sodium, calcium, iron, copper and magnesium
should not give false data.
2. The method must be able to quantify 10 parts per billion (ppb) (94 nM)
palladium in solution - As an example, if an API contains 10 ppm of
palladium in the solid state (10 mg of Pd per gram of API) and 10 mg of
such an API sample is dissolved in 1 mL of water, the resulting solution
will be 100 ppb (940 nM) Pd. This API solution may be added to a
sensor solution by, for example, 10-fold dilution (e.g.,20mL of the API
solution into 180 mL of sensor solution). Therefore, when palladium
ions are exposed to a chemodosimeter or chemosensor, the palladium
concentration may be about 10 ppb (94 nM). Even when this high
sensitivity cannot be achieved, fluorimetric methods may still be
valuable if they can provide information about the relative amounts of
palladium in API samples.
3. The method must be independent of the structures of palladium complexes
to quantify total palladium - The pharmaceutical industry is concerned
with the total amount of palladium. In order for the method to be
comparable to ICP-MS, ICP-OES or AAS, the method must be in-
dependent of the palladium species in APIs.
4. The method must not be subject to interference from APIs - An API often
binds to palladium with high anity. Even in the presence of such an
API, the fluorimetric or colorimetric method must detect all palladium
species. In order to detect 10 ppm of palladium in an API, the method
must be effective in the presence of 100 000 equivalents of API relative
to palladium by weight.
5. The method must be cheaper, faster and more user friendly than currently
used technology - Currently accepted analytical methods such as ICP-
MS continue to be the methods of choice for the quality control of final
pharmaceutical products. Fluorimetric and colorimetric methods for
palladium detection will be used by synthetic organic chemists to
identify the most effective protocol for palladium scavenging during,
not after, synthetic processes. Learning and mastering these techni-
ques should take less than a day.
6. The method must be rigorously validated by comparison with the common
standard technology - Fluorimetric and colorimetric methods are not
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