STRATEGIES TO COMPARE STATIONARY BONDED PHASES OF HPLC FOR THE PREPARATIVE OR SEMI-PREPARATIVE SEPARATION OF UNSATURATED POLYCYCLIC HYDROCARBONS BY GROUPS IN PRODUCTS DERIVED FROM PETROLEUM
Systematic methods and tools for managing the complexity
Process Operation, Monitoring & Analysis (T4-2P)
Keywords: Stationary bonded phases, unsaturated polycyclic hydrocarbons, polar compounds, comparison among bonded phases, preparative HPLC
Abstract
The unsaturated polycyclic hydrocarbons are abundant in products derived from petroleum and are of particular interest because of their role in various petrochemical processes, as well as their possible carcinogenic and mutagenic properties. The knowledge of the concentration of aromatic allows us to minimizing hydrogen consumptions in fossil fuel processing. Due to the complexity of products derived from petroleum, it is required to separate the unsaturated polycyclic hydrocarbons by classes or groups before making the characterization of the components by means of instrumental methods of analysis. Stationary phases adsorbent solids as silica and alumina have been the typical stationary phases to separate by groups the unsaturated polycyclic hydrocarbons according to the number of rings and polar compounds in products derived from petroleum, heavy oils, marine sediments, etc. These stationary phases are very polar and strongly retain polar compounds or compounds that contain O, N and S. The results are the loss of these compounds on having used solvents of intermediate polarity, deformation of the peak or the peak loses symmetry and loss of activity of the stationary phase. As a consequence, the solid adsorbent stationary phase loss reproducibility.
New preparative or semi-preparative methods in HPLC are oriented to the search of stationary bonded phases that replace to the typical stationary phases of silica and alumina to make separations by groups. The market of instrumental analysis offers a great diversity of stationary bonded phases and, therefore, it is required to develop a strategy or to implement a systematic method that allows us to compare and to select an appropriate stationary bonded phase for the preparative or semi-preparative separation of the unsaturated polycyclic hydrocarbons by groups in products derived from petroleum.
This contribution summarized methods to compare stationary bonded phases such as Si–NH2, -Si-CN, Si-R(OH)2, Si-ROR. Si-RCN, Si-R(NH2)2, Si-NO2, etc. for the compound-class HPLC separations of unsaturated polycyclic hydrocarbons and polar compounds. This comparison is based on the physical chemistry behaviour of the functional group of the stationary bonded phase, behaviour of the unsaturated polycyclic hydrocarbons under isocratic and gradient elution, regression analysis, resolution between groups, retention index and behaviour of the stationary bonded phase in real samples. We have used compound models of unsaturated polycyclic hydrocarbons and polar compounds that are ever-present in products derived from petroleum for investigating systematically the parameters, which influence their retention on stationary bonded phases. A variety of examples are interpreted and explained in terms of the molecular parameters of compound models to understand the chemical and physical processes of the HPLC stationary bonded phases. For example, comparison among stationary bonded phases of the same size, same solvents and under gradient elution has indicated that the bonded phases –NH2 and –NO2 are the best to separate unsaturated polycyclic hydrocarbons of four and five rings and they are also appropriate to investigate molecular parameters. The information obtained from regression analysis for the dependence of the log k' on the number of carbon atoms, numbers of electrons pi, number of aromatic rings and number of pi bonds of the unsaturated polycyclic hydrocarbons under isocratic elution has indicated that the bonded phases of the type nitrile can achieve the best separations according to the number of carbon atoms of the aromatic rings and number of aromatic rings. The bonded phase amine is the best to explain a linear elution of the unsaturated polycyclic hydrocarbons according to the number of carbon atoms and pi bonds.
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Presented Wednesday 19, 13:30 to 15:00, in session Process Operation, Monitoring & Analysis (T4-2P).
