Concentrating poly(A)+ mRNA

Procedure

Add 1/10 volume 3 M NaAc, pH 5.2, and 2.5 volumes 100% ethanol. Mix and incubate at -20C for at least 1 hour. Centrifuge at > 12,000 x g in a microfuge for 20 minutes at 4C. Wash the pellet twice with 80% ethanol. Air dry pellet. Check for dryness before proceeding. Resuspend pellet in RNase-, DNase-free H2O. The appropriate volume for resuspension depends on the expected yield and the amount of RNA required for the cDNA synthesis.

Reference : Affymetrix Expression Analysis Technical Manual.