Dried urine spot (DUS) applied for sampling prior to the accurate HILIC-MS/MS determination of 14 amino acids

Urine amino acid analysis has proven valuable for an array of clinical or nutritional studies. However, transportation of liquid urine sample shows certain disadvantages, such as possible leakage, need for cold chain and thus higher costs for their transport. Utilization of dried urine spots (DUS) can offer an interesting alternative. In the present study, a method was developed for the determination of 14 amino acids in DUS including the testing of in-house collection device and drying of the sample before analysis. Normal filter paper was tested as the means for sample collection. Absorption and extraction experiments were performed on 3 different types of filter paper, with 3 different extraction solvents and two different solvent volumes. The solvents used were mixtures of common analytical solvents (methanol, water, acetonitrile) using total volumes of 1 mL and 1.5 mL. Finally, 1 mL of acetonitrile: methanol: water 40:40:20 (v/v/v) was chosen as the optimal system. Analysis was performed on a UHPLC-MS system, using stable isotope labeled internal standards. Method validation included the study of limits of detection (LOD) and quantification (LOQ), linearity ranges, precision, matrix effect, extraction recovery, precision, and stability for each analyte. The obtained results were satisfactory, thus enabling application of the proposed method as an alternative to the analysis of liquid urine. Further utilization of DUS can offer advantages by enabling patient centric sampling even in long distances far from the analytical laboratories.