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MeCN Split Peaks and QuEChERS

4 Feb 2009


The “solvent effect” with splitless injection uses an initial GC oven temp 10-20°C below the solvent boiling point to refocus early eluting peaks. However, devotees of QuEChERS, which produces an acetonitrile (MeCN) extract, have likely noticed that the “solvent effect” is difficult to achieve. MeCN boils at 82°C, so a 60°C oven start should promote good chromatography. But Dichlobenil, a volatile pesticide, is split into multiple peaks (see figure). Why does this occur? A polar solvent is being injected onto a non-polar GC stationary phase, Rxi-5Sil MS. Mismatched polarity causes solvent beading (figure inset), which leads to peak splitting!

Before I blog again on this issue, I want to hear reader comments, including practiced solutions to the problem. Readers who got the paronomasia in the headline (Me Seein’ Split Peaks) get extra points. OK, I admit it; I didn’t know that a pun was a paronomasia until I went to Wikipedia.

Further reading: http://en.wikipedia.org/wiki/Pun