This article is available online at http://www.jlr.org novo pathways, such as alterations of some species of the targeted lipidomes into others. Similar to common quantitative analyses using direct MS or LC-MS that need authentic standards together with internal ones, quantitative lipidomics may also require a standard set of all lipid species targeted, because each lipid species has a different molar response in MS detection except for special cases. However, it is practically impossible to obtain all authentic species, including not only different even straight carbon chains but also odd and/or branched ones. To overcome such limitations, lipidomics researchers have contrived a novel procedure to quantify lipidomes comprehensively. Han and Gross ( 3 ) proposed a quantitative method for analyzing triglyceride molecular species using direct MS, which involves a procedure to calculate response factors for species that are not available as authentic materials, based on differences of the responses in the numbers of total carbons and double bonds among the species. For quantitative determination of phospholipid molecular species, Koivusalo et al. ( 4 ) utilized the following parameAbstract One of the key challenges in lipidomics is to quantify lipidomes of interest, as it is practically impossible to collect all authentic materials covering the targeted lipidomes. For diverse ceramides (CER) in human stratum corneum (SC) that play important physicochemical roles in the skin, we developed a novel method for quantifi cation of the overall CER species by improving our previously reported profi ling technique using normal-phase liquid chromatography-electrospray ionization-mass spectrometry (NPLC-ESI-MS). The use of simultaneous selected ion monitoring measurement of as many as 182 kinds of molecular-related ions enables the highly sensitive detection of the overall CER species, as they can be analyzed in only one SC-stripped tape as small as 5 mm × 10 mm. To comprehensively quantify CERs, including those not available as authentic species, we designed a procedure to estimate their levels using relative responses of representative authentic species covering the species targeted, considering the systematic error based on intra-/inter-day analyses. The CER levels obtained by this method were comparable to those determined by conventional thin-layer chromatography (TLC), which guarantees the validity of this method. , ceramide class consisting of non-hydroxy fatty acids and 4-sphingenines; ESI, electrospray ionization; LOD, limit of detection; LOQ, limit of quantifi cation; NPLC, normal-phase liquid chromatography; RPLC, reversed-phase liquid chromatography; RSD, relative standard deviation; SC, stratum corneum; SIM, selected ion monitoring; S/N, signal to noise; TLC, thinlayer chromatography