2.5. Sample Processing
HT
The method developed to purify the plasma and concentrate the HT metabolites was based on a previous research study [Urine samples were thawed, filtered through 0.20 µm regenerated cellulose filters (Macherey-Nagel, Düren, Germany), and immediately analyzed using UHPLC without further preparation.Plasma standards were prepared in a control plasma which did not contain the tested compounds; urine standards were prepared in water. These reference standards (5.6–0.02 mg/L) were prepared fresh for each measurement and processed in the same way as the samples.Peaks of HT metabolites were identified by comparison with reference compounds regarding retention time and MS