Fig. 4. Comparison of concentration values obtained in this and previous studies covering ceramides by MS-platforms in NIST SRM 1950.

Comparison of inter-laboratory and/or cross-platform trials reporting ceramide concentrations in NIST SRM 1950. Each open circle corresponds to the reported value from one laboratory in each of the respective studies referenced by first author and year of publication. (sp) refers to a single, standardized protocol and platform employed by all laboratories while (mp) denotes studies in which multiple protocols and platforms were used. The red boxes and numbers indicate median ±MAD (mean absolute deviation) and the number of participating laboratories, respectively. Depending on the precise nature of the study and/or reporting laboratory, concentrations were either reported with sphingoid-base and fatty acyl chain details (e.g. Cer 18:1;O2/16:0) or as sum compositions (i.e. Cer 34:1;O2). In the latter case, isobaric ceramide species other than the 4 ceramides targeted in this study may therefore have contributed to the reported concentrations. Details of the individual studies are presented in Supplementary Table 3. No outlier removal has been applied for any of the studies. Source data are provided as Source Data File.