Chromatography Forum

I was wondering what systems people are using for GPC/SEC analysis.

I am currently in the market for a new system and was wanting to get opinions from the forum on the instruments that are in use.

Any information would be greatly appreciated.

are you thinking of using a standard system with UV or/and RI?
or going for a real SEC system with a Light scattering and viscometer detector?

A good pump, delivering a stable solvent flow, pump seals which are restant to your solvent (I use THF all the time) and low S/N detectors.
I use Waters equipment and I am very satified with it. Especially the 2414 RI detector is very good. I use also an Alltech 3300 ELSD. With the latter the purity of the solvent is very important.

A GREAT pump is the heart of a GPC/ SEC system. You need a pump that will deliver very consistent flow rates at very low pulsing.
Everything else is truly secondary. The pump is KING.
I have run GPC at all temperatures including at 142 DEG C . Many years experience

I agree, that stable flow pump is the key. But also take software in account. Some (DataApex, PSS, not sure about Waters) have compensation algorithms based on marker.

Concerning hardware, PSS (Polymer Standards Service), for instance, collaborates with Agilent for years. But I saw grate results obtained with other vendors (Waters, Thermo).

Hello to all,

I do SEC/GPC with Thermo, and I have a lot of problems with RI all the time. When in method I write 35 C for RI after few sequence RI have ERROR and he dont run next sample. I am solving that problem like that now that I dont put constant temperature in method for RI, but if i do that that I dont have always same conditions for method development, isnt that right? Have anyone any tips how I can solve that problem?

Thanks to all in advance for answers.

Jabolko

where is the RI in the lab?
what is the model?
if close to a vent of ventilation then move it where it will not be influenced by the ventilation

Hello unmgvar,

yes RI is in lab (temperature of lab is 22 C). In lab is "strong" air condition, if you sit in lab you can feel air circulation. But I dont know were to move it if that is cause of my problems, I have to think of options. RI model is Accela RI detector.

Thank you.

jabolko

some solutions i know of are to divert the flow of air from the RI
or to close the RI in a perspex box
this is weird that such a new model of RI is influenced by flow of air. this is a condition from old systems generally

I have that kind of problems from begining ( error all the time) and when engineer come they say that i have to dirty sistem. But all the time I use contration of 2 mg/mL, and i always cleaning sistem on end and when i start i wash all without colum with mobil phase i wil use next,then with coulumn not in RI and then 10 volume of column. But sometimes error not want go away for all day, sometimes in beggining its ok, but then show and not want "go away", and it show sometimes after few samples were already inject. I was thinking that maybe is really problem air condition. Becouse RI have simple heater and if cold air circulation around it heat then more then if is set temperature, and becouse he have such heater, when is get worm its hard to get colder, he need time, and becouse of that its show error and not want to let that next sample is injected. Dear Unmgvar, what do you think about that?

Thanks

jabolko

can you increase the delta range of the temperature on the RI?
sometimes it is not a feature you do in the software but in the hardware?
otherwise you need to isolate the RI from the lab ventilation
see also if there is a firmware upgrade for this module that maybe solves that problem for you

hmmm I dont know about that, I have to check manual for RI. I am sure some were it have to be RSD for temperature of RI, and it is set probably on +/- 0,5 C then only in this region is READY. But I have to see if is changeable, I really dont know . I have to look. I am going to let you know how it went.

Thanks

Jabolko

Hello unmgvar,

thank you for all your help. We moved mashine out of the range were air condition is strong and now is working ok. I cant increase the delta range of temperature on the RI or i didnt find it. I even ask people which are destributer in my country for Thermo but he said it isnt posible.

Thank you unmgvar for all help, you help me a lot (with columns and RI), till now I was sure for RI that isnt clean and becouse of that show error.

Thank you.

Jabolko