by
Jake » Mon Jun 26, 2017 7:52 pm
I'm certainly not a big fan of RI, but we spent years making the typical HILIC/aminopropyl/ELSD method work for our sugar feed stocks. We tried nearly every vendors' approach to improved stability, but they all eventually failed after 100-200 samples. Rather than going that route, we ending up just buying the cheapest column we could find and treating them as disposable. We always had to run a full set of standards flanking the samples with every set. Frequently the quality of data for the replicate standards was so poor the entire set needed to rejected and re-run. Really frustrating for all involved. Everyone dreaded having to do the sugar assay. After MANY years of this, we switched to the typical ligand-exchange-RID method. The RA who first set it up was disappointed her coefficient of determination for her seven-point standard curve was only 0.9999. She was able to use the standard curve for many months, and only a single-point calibration was needed. It took us awhile to dial-in the best cation to use for the ion-exchange column due to the high salt content of some of our feed stocks. But once we got that worked out, it was smooth sailing.
A similar situation for us for generating usable, reliable, TAG profiles. Made LC/MS work for awhile, ELSD was completely useless, other than for quantitating a single or few TAGs, and we've settled on NARP/RID. It's dreadful: two 4.6 X 250 mm columns, 2.5 hour run time per sample, must start early in the day so as the method isn't running when the lab gets cold at night, column needs to be rinsed after two to three injections since it's isocratic, 50 mg/mL (!!!) injection concentration, etc. But it always works, and gives good, reliable data.
There's a reason RI is still around. While not the most cutting-edge tool in anyone's lab, sometimes it's still the best way to do something.