Chromatography Forum

Greatings from Brazil!

I am working in a Validation process of Benzydamine hydrochloride following the European Pharmacopea's method.

This method required a packed column (2 m x 2 mm) wish acid-washed, diatomaceous support (80 to 100 mesh) coated with 3% w/w of phenyl methyl silicone (50% phenyl).

In the first runs, I get good chromatograms and reproducibility. Until I had to run a prior test changing the GC set for cappilar column.

In return to packed column, I can't obtain good runs. The first run after turn on the GC is generally good, the second is bad.

The base line after the diluent peak doesn't get the zero, or the line value on the beggining of the run. The line keeps about 15000 pA and with some noisy.

Anyone can help me solve this problems?

Best regards,

Ronan Coelho
Pharmacist

‎Olá Ronan

Welcome to the forum

Regards

Ralph

Seems like there is a leak at injector side , may be a cracked ferrule or septum.

‎Olá Ronan

You say that your first injection is fine but the second one is not. Have you tried cleaning your FID jet?
Cumprimentos

Rlph

In addition to the baseline shift there are two other strange features of the chromatogram; the diluent (solvent) peak is very narrow (so narrow that I suspect it is a pressure pulse not a peak), and there is no analyte peak at all. Both of which suggest that Uzman is right - you have a massive leak at the inlet end of the column.

In addition to the baseline shift there are two other strange features of the chromatogram; the diluent (solvent) peak is very narrow (so narrow that I suspect it is a pressure pulse not a peak), and there is no analyte peak at all. Both of which suggest that Uzman is right - you have a massive leak at the inlet end of the column.

Olá Ronan

I would agree with both Peter and Uzman's observations about the solvent peak shape on the chromatogram that you posted and possible inlet problems

However, what concerns me is that you said The first run after turn on the GC is generally good, the second is bad.

That would suggest that you don't have a permanent inlet problem

Was the the chromatogram that you posted just the solvent(diluent) or solvent and analyte?

I would still check out your FID jet for cleaning

Kind regards

Ralph

Ralph is right - if it was a simple inlet leak the first run would also be bad. It is not usual practice to turn a GC off when you are not using it for short periods (overnight say) - when you turn it on are you waiting for all the hot zones to equilibriate before you do the first injection ?

Are all the flows and pressures showing the values that they should ?

Peter

The image above is the superposition of three runs (Standard solution) from the same vial.

The diluent is chloroform, so I think the shape of its peak is normal, becouse the boiling point of chloroform is about 60 °C and the method temperature is isothermal in 260 °C;

This other image (below) is a run of Standard Solution in beginning of my validation process;


In time, I'm thankfull for all your help!

Rgds

A classic case of the more you tell us, the more we can help.

The chloroform solvent will burn in the FID with a very smokey flame, and deposit lots of soot - that probably accounts for the baseline shifts.

If you can, use a different solvent (chloroform is also pretty toxic).

Nevertheless, your analyte peak looks quite reproducible in size, so maybe you can just ignore the baseline shifts.

Peter