Many members of primary aromatic amines are highly toxic, carcinogenic andmutagenic. These compounds can be formed for example by reductive cleavage of azo colorants. Azo colorants are used in big amount to color plastics, textiles and even food. The use of 22 primary aromatic amines in leather and textile products that come into contact with human skin and the oral cavity are restricted in directive 2002/61/EC. However, these restrictions remain ignorant to other products, although the plastic toys could be dangerous, too: primary aromatic amines can be formed from residual monomers (which do not react during the plastic manufacturing process). For example the hydrolysis of residual aromatic isocyanates in polyurethane adhesives yields primary aromatic amines... The small kids take everything in their mouths, and plastic toys are no exception. Could these harmful compounds migrate to their saliva? It is expedient to do migration study with artificial saliva solution for the risk assessment. The human saliva is a complex solution so it is practical to substitute it with artificial saliva solution that contains the components which are relevant from the viewpoint of the specific test. They have in common that they are electrolyte-rich aqueous buffer system. A slight release is expected during the migration study therefore the enrichment of the sample is necessary. We need to develope a sample preparation method that can separate the compounds from the salts and provide a satisfying enrichment.
The properties of the 24 compounds [22 regulated compounds, aniline (potential degradation product) and para-toluidine (isomer of ortho-toluidine)] vary between wide limits. They have different polarity, different pKa values, between them are monocyclic and bicyclic compounds, nitro- and halo-substituted derivatives, some of them are monoprotic bases and the others are diprotic bases. We strive for the best possible recovery for all the 24 compounds during the appropriate sample preparation, furthermore after the preparation we must get a sample whose compositon is compatible with the chromathographic method. Solid phase extraction (SPE) is perfect for the aforementioned necessary enrichment but the sample sometimes needs further enrichment or solvent exchange after the SPE. The evaporation could be a solution, but we must make sure of its applicability with detailed examination because of the differrent properties (polarity, volatility, etc.). It is also possible that the low molar weight compounds can not be evaporated.
During the sample preparation the compounds can adsorb on the different surfaces. In the case of plastic tools (e.g. syringe filter) maybe some compounds can migrate to the solution. Therefore, it is important to check the degree of the adsorption and the blind samples.
The stability of the compounds in solution is a fundamental question, too. We must have solutions with accurate concentrations to correct measurements, therefore the detailed examination of the compounds's stability in solution is indispensable. How long can we keep the stock solutions and work solutions in different solvents? Under what conditions can we keep them longer? We can save time and money with the knowledge of this information, therefore answering these questions is overriding importance.
Author: János Hegedűs, chemistry BSc student