RU decreasing during injection

Hi,
Did anyone have such experience? When you inject a sample, it will increase immediately and go to the plateau then after half of the injection, it starts to decrease (but the injection is not over). That is really crazy. The RU is not low, they are not noise. I tried several different concentration, they are always like this. I also tried to use short injection time(less injection volumne), but they are the same.

Did any one of you have similar problem? How did you solve the problem.
If someone could help me, that will be very helpful for me.

Hi,

We see it sometimes. The exact cause can be different.
1) injection system: by mixing between sample and flow buffer during injection the concentration of analyte is not constant (lower). use KInject and check the injection system. Clean injection loop and make sure the pumps are working correctly.

2) sample: it is possible that the sample is not homogenous. The larger molecules seems more abundant and bind first. The smaller molecules however have a higher affinity and will displace the larger molecules lowering the signal. Make a PAGE gel to look for the purity of the analyte.

3) ?: we sometimes can not find a cause....

regards

Arnoud

Something like that has happened to me. In my case the cause was that I hadnt put Tween in the sample.