Development of an on-line weak-cation exchange liquid chromatography–tandem mass spectrometric method for screening aldehyde products in biological matrices

This paper focuses on the development and optimization of an on-line weak-cation exchange SPE (WCXE) coupled to gradient HPLC with tandem MS detection. The system enables the selective purification and re-concentration of the in-vial derivatized aldehydes from plasma and urine samples. Aldehydes are important as biomarkers for oxidative stress. Using a derivatization cocktail consisting of 4-(2-(trimethylammonio)ethoxy)benzenaminium dibromide (4-APC) and NaBH3CN in the screening and detection of known and unknown aldehyde biomarkers, one can take advantage of the specific fragmentation characteristics of this derivatization reagent in MS/MS. The WCXE column gives the advantages of direct injection of the sample after protein precipitation and centrifugation into the WCXE-LC–MS/MS system. Injection volumes up to 50 μl can be injected without overloading the WCX column. Detection limits of 0.5 nM can be reached for the detection of the derivatized aldehydes. The system is robust with low intra-/inter-day variation in retention time and peak area. An in vitro model shows how derivatized aldehydes in human and rat plasma are detected. Finally, plasma treated with radical inducer shows elevated aldehyde species compared to untreated plasma.