The LC-MSD SL Model (Agilent) consists of orthogonal electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources and a single quadrupole mass analyzer. The system is capable of 0.13 amu mass accuracy, m/z range of 50 to 1,200, and positive and negative detection modes. The system is very sensitive and suitable for quantitative determination of small compounds such as lipids, steroids, peptides, drugs and metabolites.