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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: bluemoon on June 16, 2008, 06:25:03 AM

Title: High RSD between injection for HPLC system
Post by: bluemoon on June 16, 2008, 06:25:03 AM

I'm using HPLC for my analysis. I found that the peak area between injections for some of my samples are very high (RSD>2.0). i try inject again samples but the RSD for peak area is still high. Yet, the RSD for Retention time between injections is in the range 0.02-0.08.So I do not think there is leakage Samples solutions are clear. Temperature and pressure are constant. May i know are there any other reasons for this (high RSD)?   :-[

Thank You

Title: Re: High RSD between injection for HPLC system
Post by: wyrdbeer on June 17, 2008, 03:57:30 AM

There are a number of things that you could check...
Firstly have you achieved an RSD < 2.0 for this method before?
If so is your HPLC system in a good working order (eg. are the lamp and the syringe OK).
Are you getting good peak shape, if not check mobile phase or the column

Have you determined the minimum quantifiable limit for the method, is the sample preparation above this?

Title: Re: High RSD between injection for HPLC system
Post by: bluemoon on June 23, 2008, 06:14:21 AM

Notify. Thank You :) ;)

Title: Re: High RSD between injection for HPLC system
Post by: mmcqueen on August 08, 2008, 02:34:55 PM

Are you using a new column?  You may need to make several injections (20-100 depending on your sample) to activate all your stationary phase sites on your column.

Try injection a sample with higher concentration, your %RSD should go down.

Title: Re: High RSD between injection for HPLC system
Post by: JGK on August 08, 2008, 03:44:34 PM

Measuring RSD of the peak area will give you a measure of how well the injector/detector  of the system is working.

As your RT RSD is very tight the pump and MP flow would appear to be OK.

If your lamp age is not an issue, I would concentrate on the injector system as themost likely cause of your problems

Title: Re: High RSD between injection for HPLC system
Post by: sassman on August 14, 2008, 01:11:36 PM

It is probably an autosampler problem. Check the manual for your autosampler or contact tech support to see what is recommended for non-reproducible injections. You might be injecting too small of a volume or have air in your injection system. Could also be a problem with the syringe,seal,or piston in the injector.