By Michael J Reed on Thursday, July 24, 2003 - 09:24 am:
We are currently getting a huge area count on our first injection of a sequence of injections of a standard. We are injecting Carboxymethylcellulose standards dissolved in water. Mobile Phase is a Dipotassium Hydrogen Phosphate buffer at pH 6.5, and ACN. Column is SynChrompak GPC Peptide Column,4.6-50mm. Flow Rate is 0.5ml/min. We are only getting a high area count on the first injection. The following injections vary somewhat, but are still within our parameters. Any ideas would be greatly appreciated
By Anonymous on Saturday, July 26, 2003 - 04:05 am:
Do you have a needlewash?
By michael j reed on Tuesday, July 29, 2003 - 08:59 am:
Yes, we run on a agilent 1100 which rinses continously. We also put a purge cycle of 5 minutes between injections. Our RI detector is insulated very well so I don't think its a temp. fluctuating problem. Also, we run two blank injections of mobile phase before the first standard injection.
By ajayvairale on Wednesday, January 14, 2004 - 02:35 am:
dear friend what i think that you must equilabirate your system for at least 2 hours before starting the analysis
By Anonymous on Wednesday, January 14, 2004 - 10:44 am:
Are you making multiple injections from a single vial? If so, the subsequent injections are being made at slightly different conditions than the first. I've used septa that on 1100s always resulted in the first injection being far off (but lower if I remember) from the subsequent inj from that vial. Interestingly, it was only one lot of septa that did this - other lots of same septa (I think PTFE/Sil/PTFE)did not do this. Maybe try some inj w/out septa to see.
Also, recent threads have discussed the position of the drain tube relative to the injector - maybe some sort of siphon effect going on?.