make up gas

[push]

I am going to by GC 7890 with FID, TCD and NPD detectors. My carrier gas is He. Can I use 99.995% Nitrogen as a make up gas or I need connect He to make up gas inlet?

[Don_Hilton]

You can use nitrogen

[push]

Thanks.
And what about ECD that uses Nitrogen as anode gas. Can I use 99.995% N2 as a make up gas?

[cleh]

Yes. The anode gas and make up gas should be the same.

[AServiceTech]

Nitrogen makeup will give you slightly better sensitivity on an FID detector. For uECD, you may also use Argon/Methane mixture for makeup. For TCD, you will want to have the same makeup/reference gas as your carrier going into the TCD.

[roostorf]

I'm trying to set an older hp5890 for FID only and I had the exact same question, those regulators get really pricy and I was wondering if I could just go with a dual outlet cylindar regulator and just use He as both carrier and makeup gas.

[Don_Hilton]

You can use the same regulator to supply both the GC inlet and the makeup gas. Just put a "T" in the line, splitting gas to each connection on the back of the GC. Set the inlet pressure to above the mininum requied but no higher than the maximum allowed for the inlet or the makup gas connections. (And you want to be at least 20 lb above a pressure set in the GC that comes of this line.)

[roostorf]

So the carrier and makeup gases would exit the regulator as a homogenous mixture? Also one thing I don't quite understand is can a FID operate with helium instead of hydrogen? I kinda assumed an FID required hydrogen as a fuel or something.

[cleh]

You need hydrogen and air for the detector no matter what you choose for carrier and makeup gas. You can use He as carrier and makeup gas, but hydorgen as carrier gas and nitrogen as makeup gas is better.

[roostorf]

OK, that makes sense then, so no matter what you need h2 for the FID, and since its also a good carrier gas it only makes since to use hydrogen. Helium would always require a cylindar in additon to the hydrogen. According to the manuals Nitrogen and Hydrogen requre two different type of fitting regulators? I kinda thought that the cylindars were the same no matter what gas was in them, but from what I can tell regulators with 350 in the product number go with hydrogen and ones with 580 go to nitrogen. Do both tanks require two stage regulators, or is that just on the carrier gas. I'm guessing a tee goes on the hydrogen and one end goed to the detector and one to the injector, or does the FID require its own inline regulator to reduce the pressure further? I'm guessing the Nitrogen then goes in the AUX gas port. The only other question is what traps/seives/filters/purifiers do I want and do I want them on both lines. I heard oxygen traps arent supposed to be used on FID or something, and I'm not entirely sure which ones are best to use. Thanks so much and I'm sorry for hyjacking this guys thread to ask my own newbie questions, its just hard ordering all these parts and hoping that they are all gonna fit together when they get here.

also one more thing, I need a tank for zero air for the FID too? Bare minimun I need Hydrogen for detector and carrier, Nitrogen for makeup gas and Air tank for detector as well? there isnt some kind of air compressor filter system so I only need two tanks, just h2 and n2?

[Don_Hilton]

On getting traps - go to the web site (or open the catalog) for your favorite chromatographic consumables supplier. You will find traps and filters. There are sets of indicating traps that you can put close to the instrument. (I strongly recommend the indicating traps because they give you warning when you get a bad cylinder of gas. It is infrequent, but happens now and again.)

On air - yes, zero air. You are measuring a signal that indicates carbon passing through the flame. You do not want to add carbon from the air. (You do not add an oxygen trap to the air -- you are using the air for the oxygen to make a flame.)

There are compressor systems for air. These need to be oil-free compressor systems. There are several vendors - and I don't remember names at the minute. These folks usually exhibit at PittCon, so take a look at [url]pittcon.org[/url] and browse the vendor lists for the present and past meetings.

All gasses get two stage regulators. This provides even pressure to the back of the instrument. You have one regulator for air, a second for nitrogen and a third for the hydrogen. If you are going to use hydrogen as a carrier, check with the safety committee. While hydrogen is a good carrier gas - particularly for capillary chromatography, there are some people who just know that you put everybody at risk. And, they can show you pictures of the Hindenburg burning. Worse yet they can make it very difficult to set up an instrument which uses hydrogen as a carrier. With a bit of luck, you have a safety committee that will just be sure that tanks are properly strapped to a bench or wall.

Also, get a leak detector. Your chromatographic consumables supplier will have one of these as well. You do not want to use Snoop or soap solutions for testing for leaks in a system used for capillary GC.

There are also commercial hydrogen generators that will aviod having hydrogen cylinders in the lab. There is discussion of them elsewhere on this site.

[cleh]

Great advice about the safety issues with hydrogen.

Just a note, if you have a split/splitless injector on the 5890 it is has back pressure flow regulation. If the column should break in that small oven, the carrier flow stops so the oven will not fill with hydrogen. This is not the case with the packed injector.

Also, the 5890 has a flow rate adjustment built into the make up gas controller. The air and hydrogen controllers are just on and off. The flow rate is based on the pressure set at the hydrogen and air regulators. If you use one hydrogen regulator for the carrier and FID fuel your flow rate for the FID fuel would be too high. You would also need to place a single stage regulator before it goes into the FID hydrogen controller and set the flow there.

[Don_Hilton]

Do some checking - if you are installing a 7890, as indicated in the first post. the pressure and flow regulation may be avaialble in the instrument as in the 6890. If this is a new instrument, there should be a pre-installation guide to help you be sure you have everythign you need.

[lgchrom]

Using Hydrogen as a carrier gas with a split/splitless injector would probably require a fume hood for safety reasons.

[Don_Hilton]

Good laboratory ventilation should be adequate. Hydrogen diffuses very quickly, so except at the very outlet from the splilt vent, there will not be high local concentraiton. As long as air is moving through the lab and out, hydrogen should not build up to a hazardous level. If power in the lab fails, air flow will stop, but many newer GC's also stop carrier flow if the power fails.

You can exhaust the split vent to the fume hood system. In some cases, laboratories do this because of the types of compunds being vented into the room through the split vent.