Chromatography Forum

Hi all,

I've recently acquired an HP 4890A GC and would like to try running some separations purely out of academic interest. I'm a mere hobbyist and a GC virgin, so have a lot of learning ahead of me (although of course I do thoroughly understand the fundamentals of the process). There are a few issues I need a bit of assistance with in regards to this particular GC.
Firstly, I can't seem to find any user guide/operation manual online for this model, so if anyone knows where I can source one from, that'd be very helpful!!
Secondly, can I get away with just hydrogen gas only? For both carrier and for the FID? I've been offered two purities: 99.995% and 99.9995% but as just a hobbyist I really don't need the higher (much more expensive) grade one? (unless it's going to damage the column or some other component?)
Finally, I'm going to need some new septums for this machine and if anyone knows where I can order them from by post, that would be good to know.
Many thanks!

Paul

It appears that a 4890A is a stripped-down form of 5890A, so search for 5890A information.

Likely the septa would be 3/8 inch/9.5mm ones like 5890 series and 6890 series use.

Yes, you should be able to use hydrogen as the carrier gas and for fuel for the FID, we did that on our 5890 units.

For your purpose I would think you can get by with the lower grade Hydrogen, but you do need it for FID fuel gas, carrier can be Nitrogen, especially if using a packed column. I would look for a used Hydrogen generator then you only need DI water to feed it, so you don't need the extra hazard of the cylinder and plumbing.

It appears that a 4890A is a stripped-down form of 5890A, so search for 5890A information.

Likely the septa would be 3/8 inch/9.5mm ones like 5890 series and 6890 series use.

Yes, you should be able to use hydrogen as the carrier gas and for fuel for the FID, we did that on our 5890 units.

Many thanks for that. If anyone knows of a supplier of suitable septums in the UK or Europe, then that would be helpful, too.

For your purpose I would think you can get by with the lower grade Hydrogen, but you do need it for FID fuel gas, carrier can be Nitrogen, especially if using a packed column. I would look for a used Hydrogen generator then you only need DI water to feed it, so you don't need the extra hazard of the cylinder and plumbing.

Thanks for those useful tips! I hadn't even considered getting a hydrogen generator; not sure if the purity would be sufficient, but will look into it. AFAIK it's an open column 15m long. I need to google the part number to find out any peculiarities about it (hopefully none) before I go too far ordering gases, but I'll be doing that later this week if time permits.

For your purpose I would think you can get by with the lower grade Hydrogen, but you do need it for FID fuel gas, carrier can be Nitrogen, especially if using a packed column. I would look for a used Hydrogen generator then you only need DI water to feed it, so you don't need the extra hazard of the cylinder and plumbing.

Thanks for those useful tips! I hadn't even considered getting a hydrogen generator; not sure if the purity would be sufficient, but will look into it. AFAIK it's an open column 15m long. I need to google the part number to find out any peculiarities about it (hopefully none) before I go too far ordering gases, but I'll be doing that later this week if time permits.

If you use the hydrogen for the carrier and you get a generator that uses molecular sieve on the outlet, then get a moisture trap to keep the carrier gas free of water. The generator that uses the palladium frit are more expensive but give drier gas. A little moisture at the FID shouldn't hurt since you are going to be creating water vapor when the flame is on anyhow.

I run a 5890 FID on a cheapo Chinese hydrogen gas generator; water trap, hydrocarbon trap. Air comes from a hardware store pancake air compressor; double-trapped (two inline hydrocarbon traps). Smooth baseline.