variation of peak area and height

[slimshady]

I did the injections on different days with the same method and same solution. But I got quite differnt peaks with different height and area. The 2nd day's results are much larger and higher than the 1st day, But the 3rd day the results seem compatible with the 1st day's.

I checked the UV wavelength setting, i did not change it. And for each single day's injections, the peaks are reproducible. The problem only happen when I shut down the system and restart it.

Also the level of solution does not affect the results. I have injected sample with different level the results are the the same.

Any suggestion where I should check ??

[Bruce Hamilton]

I'm assuming that the retention time didn't change, you're using a UV detector, the method used to work OK, and that you used the same mobile phase solutions for all three days, and that samples/standards are stored appropriately - so evaportion or precipitation aren't issues.

If not, that would be the first action. ensure that the sufficient mobile phase is made for multiple days, and ensure that the sytem is fully flushed after the samples and before close down. Day to day variations in mobile phase absorption could change peak areas.

The most obvious cause is the detector, possibly the lamp energy. Ensure that the lamp is OK, and that if you are using a reference wavelength that also has plenty of energy available. You could run a sequence, leave all the other modules on, turn the lamp off for a couple
of hours, restart the lamp, give it an 30 mins to stabilise, and repeat the sequence. If there are variations, then your lamp or detector is the problem.

Ensure that the day to day variation of the injection module is OK, and that the reinitialisation each morning isn't affected by a defective valve or actuator. You can check this by leaving the other modukles on, and turning on the injector and performing multiple injections. Flush, turn off injector for an hour, restart, and repeat the sequence of injections.

It's all down to systematically looking at what can change at each start, and systematically working through the modules.

Please keep having fun,

Bruce Hamilton