There are publications concerning the studies on interesterification of oils with methyl and ethyl acetate using immobilized lipase as a catalyst. With this approach, triacetin (TA) could be produced instead of glycerol as the main by-product, possessing a much higher commercial value. In this study, the synthesis of biodiesel (BD) by interesterification of triglycerides (TG) and ethyl acetate in the presence of sodium methoxide catalyst has been investigated. Apart from the BD and TA, the reaction mixture may contain intermediates, such as diacyl monoacetyl glycerols (DiGlAc) and monoacyl diacetyl glycerols (MonoGlAc2). Sodium methoxide solution in methanol as a catalyst may yield also such products as monoglyceride, diglyceride and glycerol in low concentrations. The reaction mixture may also contain unreacted TG and undistilled ethyl acetate. In the case of interesterification with ethyl acetate, the degree of conversion may be low, so that the known method (EN 14105) cannot be applied because the TG concentration falls outside the conventional calibration range. In order to obtain the information concerning the composition of interesterification reaction mixtures, a new calibration procedure for the determination of TG in the range from 0.5% to 80% (wt %) was developed in the present study, and the peaks of DiGlAc and MonoGlAc2 were identified.