Vivaspin 500 30 000 mwco pes filter units

Plasma samples were collected from the arterial line or via a venous blood draw into S-Monovette EDTA K3 plasma tubes (Sarstedt; Nuembrecht, Germany), immediately put on ice, centrifuged in a precooled Thermo Scientific Heraeus Megafuge 16R (Thermo Fisher Scientific; Waltham, MA) at 3400 rpm for 10 minutes, aliquoted and stored at −80°C within 2 hours. After a maximum storage of 2 days, plasma samples were thawed, filtered through Vivaspin 500 30,000 MWCO PES filter units (Sartorius; Goettingen, Germany), acidified with 20 μl 1N hydrochloric acid per 500 μl of plasma, and refrozen under the same conditions.

Blood samples were collected via a venous blood draw or, in dialysis patients, from the arterial line into Vacuette EDTA plasma tubes or serum tubes (Greiner Bio-One GmbH, Kremsmünster, Austria), immediately put on wet ice, and centrifuged in a precooled Centrifuge 5810R (Eppendorf, Wesseling-Berzdorf, Germany) at 2000g for 10 minutes at 4 °C. Subsequently, 400 μl of the separated supernatant plasma/serum is deproteinized by filtration through Vivaspin 500 30,000 MWCO PES filter units (Sartorius, Goettingen, Germany) and acidified with 16 μl 1N hydrochloric acid. The eluate and remaining plasma/serum were aliquoted and stored at −80°C within 2 hours.
The separated supernatant was frozen on dry ice and shipped to our laboratory where samples were stored at −80°C. Samples were commonly sent in groups of 5. Within a maximum of 2 weeks after the initial blood draw, the plasma was deproteinized, acidified, and measured. For assessment of the variability of oxalate results, preanalytical conditions were adjusted as follows: (i) storage of plasma and serum at RT for 6 to 8 hours, (ii) storage of plasma on dry ice for 6 hours, and (iii) storage of plasma and eluate at −80 °C for 16.5 to 21.0 months before deproteinization and acidification.