Figure 1
Schematic depicting the carryover of buffers during sample preparation when nucleic acids (NA) are extracted using either (a) spin column centrifugation or (b) magnetic beads. Dashed red boxes highlight carryover of buffer into the eluent. Carryover buffer from the previous wash either mixes with the eluent (top dashed box in each panel) or phase separates (bottom dashed box in each panel) when the two-phase wash (TPW) is used. (c) Inset graph shows a qPCR run spiked with 5 × 104 copies λ phage DNA and λ phage primers into which we added Zymo ZR “kit extract.” (When extracting from pure water samples, we refer to the eluent as the “kit extract,” which only contains water and inhibitors originating from buffers in the extraction kits). The graph compares the reaction inhibition in a 10x extract dilution and a 2.5x extract dilution and shows the effect of adding a TPW (+TPW) during the nucleic-acid extraction step. Inhibition is similarly observed for magnetic bead extraction kits. N.D. stands for not detected. We ran 6 extractions (3 silica columns × 2 conditions) and used the same kit extract to make the high- and low-dilution conditions.
