Chromatography Forum

Hi ,and happy day to all

I am working in RP-HPLC

IF i inject just ( 100%methanol) i will see big big peak after 5 min.Even if i use different solvent alone like acetonitril or ethanol or aceton i still see this peak after 5 min .Now i carryone my analysis of some agriculture compounds for one year and i still see this peak after five mins ... BELIEVE ME i clean every thing no source of contamination because i change the syring , the column ,mobile phase , solvents thousand of times but i still see this peak !!!!!! i am worry about this

can any one help please

Hi ,and happy day to all

... BELIEVE ME i clean every thing no source of contamination because i change the syring , the column ,mobile phase , solvents thousand of times but i still see this peak !!!!!! i am worry about this

can any one help please

I won't believe you . You didn't clean injection port and associated valves.
Let us know if it helped.

Is there a chance what you're seeing is t0 noise?

What are the column dimensions & flow rate?

Thanks dears

dblux_

It comes with Shimadzu system a big syring to flush the injection port and i flush it with 20 ml ( 100%) then 10 ml then five but i still see this peak .Actually, i don't know how to clean the valve but i degassed the water methanol mobile phase then the system has online degassing but i still see it every day ( since 12 months oh my god )


tom jupille

My supervisor is also suprise why this is happen and i really don't know if it is t0 or not but if it is t0 why it comes always with any solvents any column any things even if inject blank sample .The column dimension is ( 250*4.6 c18 nemesis column ) .Do you thing i leave it because this is come after five min and my analyte eluted after 9,12 min but i am worry that in the viva they will say that all are rubish ( hope not )

Thanks dears

dblux_

....Actually, i don't know how to clean the valve but i degassed the water methanol mobile phase then the system has online degassing but i still see it every day ( since 12 months oh my god )
.............

In fact, after so many injections, remains of contaminants ad/absorbed on valve's rotor should be washed out. IMHO cleaning injection valve demands dismantling it and sonication. It's only my thought, not necessarily true.
Is your method isocratic or gradient ? If iso, aquire pressure signal and check for abnormal changes during run.
Try to reduce the flow by 2 and observe what's going with retention time of contaminant peak.
Finally if your system is equipped with DAD you may try to identify the contaminant on it's spectrum. Just my thoughts which my lead you to the solution.

As Tom pointed out (above) information about the flow rate is needed - in addition to the column dimensions!

Best Regards

Coudl you give example chromatogram with this peak ?:) and the timetable of your gradient ?

Hi ,and happy day to all

I am working in RP-HPLC

IF i inject just ( 100%methanol) i will see big big peak after 5 min.Even if i use different solvent alone like acetonitril or ethanol or aceton i still see this peak after 5 min .Now i carryone my analysis of some agriculture compounds for one year and i still see this peak after five mins ... BELIEVE ME i clean every thing no source of contamination because i change the syring , the column ,mobile phase , solvents thousand of times but i still see this peak !!!!!! i am worry about this

can any one help please

Systematic approach demand to identify what part of instrument causes problem (mobile phase or autosampler to simplify).

So run a blank run (without injection) and if the problem still exist it's not related to injection port nor switching valve.

to be cont. after above steps

what detector are you using?

Seems the chance of a normal flow rate is high here, so I would think that the chance is 99+% that some people are trying to wash system peaks away. (In other words, what Tom and Dancho are trying to get at is to establish that this is just some sort of very common dead time effect).

hi,
I think the type of your dedector and the working wave lengths are very important. and it is good not to get that comtaninant peak when you change your solvent. it made me thing that the problem comes from the nature of it. if you are using photo diode dedector try to get a wide band spectrum to be clear about he wavelength and inject your sample/standart with those alternative wavelengths.
I hope this would solve your problem.

My flow rate is 1ml/min
my detector is Uv vis

When i have done blank run without injection i don't see the peak .I just see this peak when i inject any solvent even if i inject only water !!

Do i need to change the septume inside the injection port? .In other instrument ( my friend instrument ) i didn't find the peak but only this happen with my system .

please suggest to me any things i will do it and see ?

My flow rate is 1ml/min
my detector is Uv vis

When i have done blank run without injection i don't see the peak .I just see this peak when i inject any solvent even if i inject only water !!

Do i need to change the septume inside the injection port? .In other instrument ( my friend instrument ) i didn't find the peak but only this happen with my system .

please suggest to me any things i will do it and see ?

So the problem is associated with autosampler. Now I would try to inject mobile phase of the composition exactly as your starting MP composition and observe whether peak is present. If YES - I would suspect contaminated switching valve.

My flow rate is 1ml/min
my detector is Uv vis

When i have done blank run without injection i don't see the peak .I just see this peak when i inject any solvent even if i inject only water !!

Do i need to change the septume inside the injection port? .In other instrument ( my friend instrument ) i didn't find the peak but only this happen with my system .

please suggest to me any things i will do it and see ?

Have you tried to inject a clean solvent several time and changing the injection volume : 1; 5; 10 microlitter and see if the ghost peak changes in size ?
Strange really.

This is simply what Tom mentioned above.