You are estimating between syringe markings, introducing up to 8% measurement error
Premature cell senescence in human skin: Dual face in chronic acquired pigmentary disorders
these were bile acid metabolites such as cholate and chenodeoxycholate, lipid metabolites such as arachidonic acid, C16:0-LPC, C18:0-SM, docosapentaenoate, adrenic acid and stearoyl ethanolamide, metabolites involved in the metabolism of protein or amino acids, such as imidazole propionate, ADMA and creatine, and active metabolites or neurotransmitters such as the n-acetylputrescine, diacetylspermine, malonate
(PubMed) Douaud G, Refsum H, de Jager CA, et al
Methodological aspects of bio-logically active compounds quantification in the genus Hypericum