Identification of acylcarnitines by MS/MS. Experimental MS/MS fragmentations of (A) valerylcarnitine, (B) hydroxyvalerylcarnitine, (C) octenoylcarnitine and (D) octanoylcarnitine are juxtaposed below a library MS/MS fragmentation of methylbutyroylcarnitine. Diagnostic fragments common between library and experimental fragmentations are labeled. Pertinent MS/MS peaks are labeled for mass-to-charge ratio (m/z) by broken line. Additionally, distinctive fragments equivalent in mass difference to that of the mass difference between the represented acylcarnitine and methylbutyroylcarnitine are labeled with proposed fragment structure displayed. MS/MS peaks and matching proposed fragment structure are labeled by dotted line.