Preparation of Pure Calibrants

One of the most difficult problems faced in the project was the lack of commercially available calibrants. Consequently, a set of calibrants was especially prepared for the purpose of the interlaboratory studies and certification. A full description of the synthesis is given elsewhere [126]. 

Arsenocholine was synthesized from arsenic trichloride, producing first trimethylarsine by addition of MeLi, followed by conversion of the trimethyl-arsine into arsenocholine by addition of bromoethanol. Arsenobetaine was prepared from trimethylarsine (synthesized from commercial arsenic trichloride). 

The purity of the compounds was characterized by elemental analysis, molecular analysis ( H NMR, mass spectrometry), thermodifferential and thermogravimetric analysis and separative techniques such as HPLC, GC and capillary zone electrophoresis [127]. This procedure provided highly pure products for use in the interlaboratory studies, e.g. arsenobetaine was shown to be more than 99.8% pure. 

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Lagarde, F., Asfari, Z., Leroy, M.J.F., Demesmay, C., Olle, M., Lamotte, A., Leperchec, R and Maier, E.A. (1999b) Preparation of pure calibrants (arsenobetaine and arseno-choline) for arsenic speciation studies and certification of an arsenobetaine solution (CRM 626). Fresenius f. Anal. Chem., 363, 12. 

Beside the preparation of pure calibrants for the purpose of certification, independent studies were carried out to investigate possible sources of error existing at the extraction and derivatization steps. The study on derivatization demonstrated that the yields obtained by Grignard reactions were generally... 

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