Chromatography Forum

The autosampler Varian CP-8400 has one option for injecting internal standard. In routine test we should make a mixture of sample and internal and inject result solution by hand or autosampler. When we make these solution internal standard will be diluted by sample. For example 50 ul internal(about 0.0350 gr) in 100 ml sample will make a solution of a about 0.04 % internal. If I want to use autosampler for these type of sample, how to proceeds? I think I should make a solution of internal separately and autosampler take from that. In these case the solvent for internal maybe interference with other peaks. What is the correct way? our gc system is Varian CP-3800

Use the same solvent for the internal standard as for the samples.

Peter

Dear Peter

the sample is styrene and that mean i should make a soultion of internal in styrene. but i think it can effect amount of impurites which should be determined . sample inculde impurities itself and other parts will be added from internal solution. am i right?

So your sample (styrene) is also your solvent ? In this case the problem is actually just to add a small enough quantity of internal standard to the small quantity of sample in the autosampler vial. Since you usually add 50 ul to 100 ml, simple maths says that you need to add 0.5 ul to 1 ml.

Peter

dear peter
i want to take internal by autosampler not ourself. in case of 5ul internal in 1 ml sample(equal to solvent) we should prepare that solution in a vial because autosample could take sample from vial only and inject. i hope could be found a solvent for making internal solution and place that in autosampler vial ,after that autosampler will take 0.5 ul from internal soltion vial and 0.5 ul form sample vial for example. so in the syring we will have an approximatly soltion of sample and dilute internal. did you have any advise?

Unless I misundertsnad the problem all that you have to do is to accurately measure 1 ml of sample into a sample vial, and then use the autosampler to add 0.5 (not 5) ul of pure internal standard to it. The syringe will have to be very thoroughly rinsed between adding the standard and injecting the sample of course.

Peter

dear peter
thank you for your respons. the promblem is in autosampler operation. as i know in 8400 autosampler, the syring can not be able to add sample(intrnal i means) into vial. how could program autosample to add 0.5 ul internal to vial . usually autosampler withdraw sample from vial and inject to coulmn.

In the very first sentence of your first post you say that the autosampler has one option to inject internal standard. Now you say that it cannot add internal standard. I do not know how to make the autosampler do something that it cannot do.

Peter

dear peter
sorry for unclear explanation. in the internal option of autosample, it take define amount of internal from internal vial and then take defined amount of sample. so sample and internal will be in the syring of autosampler and then inject them. we can suppose internal and sample will be mixe inside the of autosampler syring. it seems the only way to use option is making dilute internal solution.

OK, now I understand the problem. The only solution that I can think of is to dissolve the internal standard in a solvent that elutes after the styrene and the impurities that you are interested in. Beware that you may see some distortions of peak shape due to solvent effects.

Peter