Baseline Jump

[Davidsonchemgrad]

We are currently having a jump in our baseline around 2 minutes into our runtime. The baseline jumps to like 0.06 AU at this time, but then remains straight and smooth from then on out. What could cause this problem? I can obviously give more detailed information if it is necessary and may even be able to embed a spectrum. Thanks!

[yzhen77]

check the detector. I know sometimes the baseline jumps when the wave length was changed.
zhen

[firework1]

take off column, and make a blank injection again. see if baseline jumps and at what time it jumps this time.

[unmgvar]

that is your void volume of the system.

in all systems when the final part of the injection takes place a valve is turned and then your sample is pushed by your mobile phase into the column.
that process results in a disturbance in the baseline which is seen as you describe it.
that disturbance then travels along in the system until it reaches the detector.
the time of appearance it directly related to your flow rate and system volume, including column volume.

[Davidsonchemgrad]

This is what I am seeing right here.

The first chromatogram is from a run last night.
The second is from a run last week sometime.



You can see the void volume in both of them. My understanding of the void volume was that it travels through the column, hits the detector, and then straight to the waste container just as a sample would go through the column be detected and yield a peak at a certain time. How could the void volume cause the baseline to remain at 0.06 AU. Thanks

[unmgvar]

Davidsonchemgrad

the spikes in the baseline are the valve change effect.
the baseline drift is 2 possible things:
1. the most probable- you have set a step gradient in your pump method and you simply see the effect. a change in the composition of your solvents which translate into a change of response.
2. less probable because of the location in the chromatogram: you have set a wavelenght change in your uv program without an autozero command. this is less probable because your drift is right at the begining of the run and more in accordance with a step gradient.