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- Posts: 7
- Joined: Thu Oct 13, 2011 7:46 pm
We are having some issues with particulates. We currently use a modified quechers extraction to analyze for 160 or so pesticides in potatoes (and other matrices, but potatoes are our main focus and where we see this issue the most). We extract with acetonitrile, dry with NaCl, clean up with MgSO4 and LC-NH2, solvent exchange into MeOH and filter through a PTFE syringe filter into an autosampler vial for analysis on both GC/MS and LC/MS. In the past, when we did our solvent exchange we would reconstitute with MTBE for GC/MS analysis then we would do another solvent exchange in the autosampler vial and reconstitute in MeOH for LC/MS analysis. When we did this final exchange, there would be quite a bit of white floating particulate in the bottom of the vial. Once we vortexed the vial, the particulate would gather into one solid mass which we would then have to re-filter into another set of autosampler vials before analyzing on LC/MS. This was very costly since we would need an additional set of autosampler vials (not cheap), another set of syringes and syringe filters (not cheap), plus the time spent (another hour or so). We have since attempted to run GC/MS analysis with MeOH as our sample solvent which appears to work for the most part, but now we have some sort of black particulates floating in the autosampler vials after a couple of hours. This disappears completely if shaken or vortexed, but we are still perplexed as to where it is coming from in the first place. It doesn't seem like ANY kind of particulates would be good for the instruments, even if it does disappear/disolve so easily. We have spent many hours troubleshooting this problem by eliminating one part of the process at a time. We still cannot figure out where this is coming from. We use Optima or better quality solvents, we have used different syringe filter brands, different conicals, different solvent brands. We are at our wits end. Any suggestions?