Monosaccharide composition has been determined by several chromatographic methods such as TLC, HPLC, GLC and recently by CZE. Inclusion of MS analysis coupled to GLC provides a great method than the other techniques, giving rise to highest resolved and sharp chromatograms that can be easily identified and quantified. Although, sugars were not volatile, and many reagents are used for sample derivatization, such as TMS, (CH₃CO)₂O, (CF₃CO)₂O and (CF₃CF₂CF₂CO)₂O, and none was really better than the other, in this case the application determines the choice of the derivatizing reagent. We now describe a novel method for monosaccharide determination using partially acetylated isopropylidene derivatives for GC-MS examination. Commercial Gal, Glc, Man, Fuc, Rha, Rib, Ara, Xyl were obtained from Sigma-Aldrich, MO, U.S.A (100ug) of each monosaccharide was dissolved in acetone containing traces of H₂SO₄ at 100^oC for 2 h, giving rise to specific di-O-isopropylidenes derivatives. The solution was then neutralized with NH₄OH, centrifuged and evaporated. The residue was acetylated with Ac₂O-pyridine (500 ul; 1:2, v/v) for 30 mim. at room temperature. The PADIP (partially acetylated di-isopropylidene) were extracted with CHCl₃ and washed with aqueous CuSO₄ solution and the organic layer containing PADIPs was submitted to GC-MS analysis (OV-225 fused silica capillary column. program: 50ºC /40ºC min to 230ºC, maintained for 10 min). The chromatogram showed seven resolved peaks which correspond to each PADIP, the derivatives were two times faster than the conventional alditol-acetates derivatives, and no mixture of anomers as well as pyranosidic and furanosidic conformers were also observed, which are commonly found in trimethylsilylated and trifluoroacetylated derivatives. The EI-MS spectra of each monosaccharide showed a pattern of fragmentation, which was specific for each monosaccharide class and ring conformation, the ions at 43, 83, 85, 100, 101, 127 and 129 m/z are found in all PADIPs derivatives in different ratios. The presence of molecular ions were not observed, however a characteristic daughter ion was observed [M-15]⁺ for all sugars varying from 30 to 100%, and the ion [M-73]⁺ was observed only for hexoses and Rha. The method showed to be very easily, specific, sensitive and 2 or 10 times cheaper than those obtained by silylation and fluoroacylation, and showed to be faster than the classic alditol-acetate method.