A quantitative analysis of serum sulfatide by matrix-assisted laser desorption ionization time-of-flight mass spectrometry with delayed ion extraction.

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry with delayed ion extraction (DE MALDI-TOF MS) was applied for the first time for the quantitation of sulfatide content in serum at the picomole level. The total lipids extracted by n-hexane:isopropanol (3:2, v/v) from 100 microliter of serum were saponified to convert sulfatide to its lyso form, and then the lysosulfatide was directly determined using DE MALDI-TOF MS in the presence of other degraded lipids. Hydrogenated N-acetyl lysosulfatide was used as an internal standard. The relative peak height of sulfatide was calculated and plotted versus its contents. This plot showed linearity between 2 pmol and 1 nmol of sulfatide (regression coefficient r > 0.95). Sulfatide contents of normal human sera and rabbit serum were quantitated by this method. The results corresponded well to the reported data determined by gas-liquid chromatography. This new approach was found to be sensitive, convenient, and reliable. It is expected to be applied to quantitate sulfatide from other small amounts of body fluids or tissues and to clinical examination. It is also expected to be applicable to quantitate other glycosphingolipids.