Trioctylphosphine oxide (TOPO) always contains impurities from intermediary products used in its preparation or from secondary reactions occurring during this preparation. Most of these impurities are low-molecular-weight compounds which can be identified. They are basically on the one hand dioctylmonophosphinic acid (Al) and monooctyldiphosphonic acid (A2) and on the other hand Lewis bases such as dioctylphosphine oxide (DOPO) and dioctylphosphinate. The conditions are well known for the separation of these compounds by gas chromatography (GC) using a capillary column as mentioned by Gyllenhaal and Stuurman' . Although this technique is well adapted to the determination of TOPO, it is not suitable for the analysis of the two acids. Indeed, after silylation, a temperature of 300Β°C is required in order to separate these compounds and the results obtained are poorly reproducible because of the instability of the produced derivatives at such a temperature. A technique allowing the separation of the ionic compounds is isotachophoresis (ITP) as described by BoEek et uZ.~ for the separation of the degradation products of tributyl phosphate. We observed that it gave also good results for the separation of the Al and A2 acids but could not be applied to separate the other non-ionic impurities or TOP0 itself.
Ionizable compounds can be separated without derivatization by reversedphase ion-pair chromatography systems which make possible the simultaneous separation of non-ionized compounds. This paper deals with the elaboration of simple high-performance liquid chromatographic (HPLC) systems which permit the separation and to determination of some of these compounds. We did not try to separate compounds of higher molecular weight which can also be identified, by liquid chromatography under modified conditions or by gel permeation chromatography (GPC), as impurities in some samples of trioctylphosphine oxide.
EXPERIMENTAL
Apparatus
The HPLC equipment was a Waters Model M740 liquid chromatograph