Problems with injections

[Alex Buske]

Autosampler is an ultimate. Do you mean, the rinse for the autosampler syringe needs to similar to the mobile phase, because currently I've been using 50/50 Methanol/water for all methods.

The ultimates i know draw the sample into the loop by the syringe and the put the whole loop in the flow path. So you will get solvent int the syringe. don't think this is a good idea as 50/50 Methanol/water and 50/50 cyclohexane/n-heptane don't mix. take a close look at the syringe.

- is the syringe solvent degassed?
- any bubbles in the syringe?
- do you puncture the vials, (500 µl is a lot)?
- is there enough sample in the vial (sounds stupid, however, we had issues other months with very very experienced stuff)?
- are the connections between needle and loop tight?

Good luck,

Alex

(Who is enjoing precise 1000µl-injections on a ultimate sampler)

[unmgvar]

yes you should change the solvent used for the wash in the sampler, or at least check the missibility between it and the mobile phase
it is also the solvent that does the drawing from the syringe and it mixes with the mobile phase in the buffer loop as sample is drawn
it is highly possible this is one of the main reasons for your problem

i also thought of something else
you are probably using a non-slit septa,
did you use the puncture offset command of the ultimate to do vapor pressure equilibration for the vial? it should be at least 1mm in your case

[nellermann]

Thanks for all your help! I'll keep you all posted on what happens next week.

Natalie

[hakunamatata]

hi..i don't know if i'm in the right thread but currently i'm having a problem with my agilent hplc 1200 series. there's a bubble in the capillary after sample injection. causing my pressure down to almost 0 and noisy peaks. i have no idea why is this happening, I've check my solvent, vial etc, no problem. there's no bubble in the capillary during flushing or when there's no sample injected. it only happen after sample was injected and happens until the end of analysis time. what happen actually and how to fixed this? pls help me.

[Uros]

Did you set your software, to handle 500 uL loop?


hakunamatata, check the rotor seal of your sampler valve. My guess is, it is overworn.

[hakunamatata]

no, i didnt set it, i also didnt check the rotor seal, if it is overworn, it needs to be replaced right? but the problem is, we didn't any extra or backup rotor seal.

[Uros]

hakunamatata the software setting was meant for nellermann, who started the thread,

The rotor seal (vespel) has part number 0100-1853. If you follow the capillary from pump to ALS you wil find 6-port valve with three screws. unwind capillaries and screws and you will find inside rotor seal with two tiny chanels.