In many cases standardised tests meet the need,but in an increasing number of cases more advanced knowledge of the chemistry is required due to the presence of complex or labile structures which are not easily analysed using standard tests. Certain substances possess physical and chemical properties which make the testing and interpretation of the data difficult.
Typical examples are substances which may have low water solubility, are extremely volatile (making maintenance of a known concentration difficult), are hydrolytically or photolytically unstable, absorb onto glass or other solid surfaces or are simply complex substances containing a significant number of unidentified components.Specific recent examples where unique tests have been developed include a molecule with multiple ionisable groups, hence multiple pKa values and consequently the ability to exist in different forms at different pH.
The use of predictive software packages to calculate pKa values allowed targeted experimentation for the accurate measurement of water solubility and partition coefficient parameters.
Often when a substance is readily hydrolysed its solubility in water may appear artificially high as a consequence of the hydrolysis products having greater solubility in water. In these cases it is important that we are able to accurately determine the structure of the hydrolysis products and develop methods (usually based on chromatography with MS detection) capable of accurately quantifying the hydrolysis product concentration.
On a specific sample readily dissociated on contact with water making detection of the parent compound impossible, but by selectively targeting a sulphur atom present in the molecule the laboratory were able to develop a method (using a Tox analyser) to determine water solubility of the target compound at sub ppm levels.
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