Chromatography Forum

Hi everyone,

I work with an Agilent 7890B GC system. I have a estándar method to cuantify 8 analites, The method specifies to use a cyanopropylphenyl 14% - dimethylpolisiloxan 86% 60m, i.d.0.25 mm, 0,25 um film column but i have another column, same movile fase but with this dimentions 60 m, i.d. 0.32 mm, 1 um film, When i inject a sample i can see al the analites but when i inyect the std no analites are visible. I preparate several times the std. My question is this, if the dimentions of the column change, i have to change another parameter to?, Vol injection, temperaturr of the oven, temperature of injector?, temperature of detector?, any flows?,

any help will be accepted, thanks

You need to increase the volume flow rate of the carrier gas, but if you are specifying a linear flow rate in the settings on the the GC the software will take care of that.

Since your column has 4 x the film thickness I would expect longer retention times than with the specified column, but if you are seeing your analytes in samples that is obviously not a problem.

What is the concentration of analyte in the standards compared to what is (expected) in the samples ? If you inject a 10 x concentration of the standard do you see peaks ?

Peter

I´ll increase the volumen flow, when i try it, no analite was retained.. i Increase the flow from 2.9 ml/min to 6ml/min

I´ll increase the volumen flow, when i try it, no analite was retained.. i Increase the flow from 2.9 ml/min to 6ml/min

2.9 ml/min is OK for that column. Do not increase it to 6 ml/min.

If you can see analyte peaks in the samples, but not in the standards it can only be because the standards are much more dilute than the samples. You need to increase the concentration of the standards until you can see the peaks. How do you know that the peaks you see in the samples are due to the analytes that you are interested in ?

Peter