Hi everyone,
I hope you are well and stay safe.
I am an operator for GC-MS instrumental and my company replace the column with another new one which called DB-WAX (60m*0.250mm*0.25microm).
A carrier gas is Helium,
The initial pressure is 2.0 psi,
The initial temperature is 60 Celsius whereas the finial is 240 Celsius.
my company specialized in fine fragrances so when I made an injection I saw that the retention time of the graph is increased with passed time and that didn’t happen in the old column 30m. the pic. below has shown the separation of a peak.
So could you please tell me what’s the best parameters and conditions for DB-WAX (60m*0.250mm*0.25microm) in the fragrances field. thanks in advance.
Hi,
At first i have a question: have you performed condition process for the new column, based on the manufacturer's guideline?
a chromatogram like yours, which has increasing base line in high temperatures, is a indicator for the column bleeding. Any new column must be subjected to conditioning for a sufficient period of time for stabilizing the stationary phase.You can find more info about this in column's manufacturer website.
In the other hand, each instrument has its own initial settings which are presented in their operation guide catalogue. For example typical pressure settings for carrier gas when you are using a column (30 m) is totally different with another (60 m). It is right also about other differences like column ID. I think you must reconsider the pressure settings.
A few remarks:
the pressure you indicated (2.0psi) is too far from the optimal range, giving a 0.25 mL/min flow: this is quite clear from your picture, where peaks are broadening at higher temperatures. Set the flow (constant flow in GC/MS!) to 1.4 - 2.0 mL/min - the starting pressure should be 25-32 psi at 60°C. Then condition the column according to the manufacturer specs and run a well-known sample from your lab.
Good work and keep us posted
Dear Ahmad Emad,
i think you use an Agilent GC-MS System (Your chromatogramm window reminds me).
May be it is a good choice to set up the columnflow in a other way.
Open the Columnfolder in your Instrument control and set there the Velocity for the Carriergas to its optimum.This is for He the range of 32- 34 cm/sec (HETP-curve minimum). Flow and Pressure will be calculated. Activate constant flow, if not done . Please check, that the outlet is set to vacuum, otherwise the calculation is wrong.
In this way you get best flow condition for your column.
Your temperature program depends of course on your analytes, but should not exceed the maximum temperature of your column.
Good sucess in your work and stay healthy
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