Stability of Chemical Species in Solutions

As a complementary comment on calibration, it should be noted that the stability of chemical species in solution is of the utmost importance in terms of quality assurance. Calibrant solutions should obviously be prepared and stored in such a way that they remain stable over a specified duration. 

The BCR experience related to the stability of chemical species in solution during storage has been summarized in a survey [51] in which causes of instability are discussed, e.g. chemical reaction between species, effects of container material, microbial activity, temperature, pH and light. The various stability experiments on chemical species in solution and the resulting storage precautions are developed in the various chapters of this book. Here we will only consider general aspects. 

The container material has to be carefully chosen to avoid undesirable effects such as adsorption of the analyte onto the vessel walls or contamination of the solutions. Thus adsorption of organotins onto PTFE and glass has been 

Microbial activity must be prevented since it may lead to possible methyla-tion reactions, e.g. of inorganic antimony [16] or mercury species [54], and biodegradation, e.g. debutylation of tributyltin to monobutyltin [55]. Biological effects are generally dependent on the temperature. Therefore, it is necessary to control and monitor the temperature at which solutions are kept. The pH of the media is a parameter that strongly affects stability, mainly of inorganic species. 

Light is one of the major causes of instability of organometallic compounds. With the exception of some compounds e.g. arsenobetaine), the metal-carbon bond is generally weak enough to be photodegraded hence solutions containing organometallic compounds are recommended to be kept in the dark in opaque containers. 

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