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Avoiding Split Peaks in Gas Chromatography for QuEChERS Extracts in Acetonitrile

By
  • Jack Cochran
Tags
  • #Pesticides (Multiresidue)
  • #Troubleshooting
  • #Q-sep QuEChERS Sample Prep
  • #Rxi GC Columns
  • #Food
  • #Method Optimization
  • #Fused Silica Capillary Columns
  • #QuEChERS
  • #Blogs
  • #Environmental & Industrial Exposure
  • #Food & Agriculture
  • #GC
  • #Injection Techniques
  • #QuEChERS
  • #Sample Preparation Products
  • #GC Columns
  • #Columns
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Acetonitrile injections don’t damage Rxi-5Sil MS GC columns. But urban legends persist, so analysts sometimes do unnecessary and laborious solvent exchanges for QuEChERS extracts.

A real problem that might warrant solvent exchange is mismatch between the polar solvent acetonitrile and non-polar pesticide GC columns (e.g. DB-5ms, Rxi-5Sil MS). Upon injection, lack of wetting leads to split GC peaks, especially severe for early eluters. Adjusting GC oven start temperatures rarely eliminates the problem.

A simple method for avoiding split GC peaks for acetonitrile extracts is to add toluene to the extract. At 50% toluene, peak splitting is gone, and sensitivity is only reduced by 2 (not even that, considering height reduction of split peaks). Even 25% toluene can eradicate peak splitting. Adding internal standard in toluene to a QuEChERS extract prior to injection is an elegant way to kill two European Starlings with one Accrington brick. And, no solvent exchange!

Comments

[…] GC columns (like Rxi-5ms, e.g.) using splitless injection can be problematic because of the classic solvent – stationary phase mismatch.  To avoid split peaks we usually have an initial GC oven temperature slightly above the 82°C […]

[...] Also Mixing with another solvent, like toluene, may also help, see: Some excellent work was done by Jack Cochran to fix this:   http://blog.restek.com/?p=638 [...]