Injection Linearity and Repeatability Issue / Agilent 1100

[sga]

Hello Friends,

Case: 1100 System with a 1313 AS & 1315 UV detector. We are validating a system using a Coffein standard solution.

The 1313A Autosample seems to be work perfectly from 0.1 to 2 micro-liter injection. This was verified using 5 injections each at various intermediate injection quantities and a line of fit with an r(sqr) >0.999

However at 3 micro-liter and above the auto-sampler behaves un-reliably. If I make 5 injections, 3 will be linear and two will report absorbance areas 1.2 to 1.5 times the expected.

I have tried this with 10 microL, 5 microL and 3 microL. In every case, one or more result is out of syc.

I have tried to change the setting for the Seat-Capilary capacity from 2.3 microL to 100 microL, but this does not make any difference.

Does any one know why an Autosampler shows unreliability in the above 3 microL range ?

Thanks and Regards

_

[Consumer Products Guy]

OK, we assume that retention time is not changing, so that the pumping system is not a part of this.

I would concentrate on these areas:

2. small leak at the needle/needle seat interface

1. metering seal (same part as pump piston seal) in the metering assembly in the autosampler module. the piston here is also the same as used in the 1100 pump.

3. check that the injection loop capillary doesn't have a small break in the weld where it changes from 1/32 inch to 1/16 inch at the ends.

[HPLCaddict]

It might be not a problem of the autosampler. Could it be that at 3ul and above you're simply out of the linear range of the detector?

[Ansh]

A shot in the dark kind of reply here. Is there any obstruction in the needle or the injection path?

[sga]

Hello,

So therent does appear to be variability in the Pumping pressure and the retention time. Is there some kind of preventive maintenance that one can do to get a more constant pressure.

Regards