Determination of urinary malondialdehyde by isotope dilution LC-MS/MS with automated solid-phase extraction: A cautionary note on derivatization optimization

► We developed an online SPE LC-MS/MS method for a rapid urinary MDA measurement. ► Urine was directly analyzed within 10 min following DNPH derivatization with LOD of 0.08 pmol. ► We investigated the optimal addition of DNPH and measured urines of coke-oven workers. ► Urines required 100-times higher amount of DNPH than MDA standard solutions. ► Urinary MDA was significantly associated with the COEs and smoking exposure.