Hp 1100 hplc system

Nurse technicians collected a fasting (8 h) venous blood sample (approximately 10 ml) on the morning of the scheduled day in both evaluations. Blood Hb was determined at the time of blood collection by a portable haemoglobinometer (Hemocue ® Hb301; Hemocue) (17) . The serum samples were collected in a dry test tube, protected from light and centrifuged within 2 h of collection. Serum was frozen at -20°C before it was sent to the Laboratory of Human Nutrition (School of Public Health, University of São Paulo) on dry ice and maintained at -70°C until analysis (within 6 months of blood drawn). Serum concentrations of retinol, β-carotene and 25-hydroxy vitamin D 3 were measured using HPLC methods (HP-1100 HPLC system; Hewlett Packard) (18) . At the second evaluation, C-reactive protein (CRP) was measured as a marker of acute inflammation, using an IMMAGE Immunochemistry System (Beckman Coulter). Biochemical data were double-typed using Excel for Windows and then converted to Stata 14.0 for data processing and analysis. Intra-and inter-assay CV were <7 %.

Samples were analyzed by LC-MS/MS (HP1100 HPLC system supplied by Hewlett Packard, Quattro Ultima mass spectrometer supplied by Micromass; Waters, Milford, MA). Electrospray ionization mode was used. For HPLC, a Waters Symmetry C8 3.5 mm (2.1 Â 30 mm) column was used, injecting 10 ml of each sample. The mobile phase was water plus 0.1% formic acid and methanol plus 0.1% formic acid.