2.2. Preparation of standard solutions
Stock solutions of proline, phloroglucinol, mannitol, all fatty
acids and sterols, as well as of the internal standards (IS) norvaline,
methyl linolelaidate and desmosterol were prepared individually
in ethanol and kept at 20 C until analysis. Calibration solutions
for phloroglucinol and mannitol were prepared by diluting each
stock solution in appropriate amounts with ethanol in the concentration
range of 1.50–50.00 lg/ml for both compounds