New to Gas Chromatography with questions

[jamesrh]

I may be asking a bit more than I should here but, I am very new to Gas Chromatography and would greatly appreciate any help I can get.

Background:
I "inherited" a job with a company that does Natural Gas Measurement, which consists of installing, calibrating, and maintaining meters for companies that produce oil and natural gas. We also collect and analyze gas samples to determine the content of the gas so our customers can have data to ensure that their reported volumes are correct when dealing with purchasers.

I have 2 Varian CP-3800 gas chromatographs that I run samples on daily. The boss who taught me how to run them had over 20+ years experience in the field and these were his 2nd and 3rd machines. He retired a bit earlier than I expected him to and only taught me the basics about the chromatographs.
I understand how to make sure the machines are physically ready to run samples, how to inject samples, what they do while running a sample, and how to read an analysis. I am only asking questions because I cannot find an type of manual or other instructions online that contain answers that I can use.

My questions are actually very basic and might sound foolish, but:
According to my (now former) boss, if we put the chromatographs on a "Standby" method for more than an hour or so they need over 8 hours to fully stabilize after activating an "Analyzing" method. Question: Is there actually a minimum amount of time that I need to wait after re-activating a chromatograph before I run samples? When I put them on Standby for a few minutes to change gas tanks I usually wait at least 30 minutes after re-activating a method before I run samples (per Boss' instructions, so the columns can re-heat or the helium flow can clear). Do I need to wait any longer any other time?
Also, my boss also stated that unless there was a power outage the chromatographs should always stay on partly because of the question stated above and he said that turning the machines themselves off and on too often could cause issues when re-starting them. I've read a couple of posts on this forum regarding chromatographs getting stuck when initializing but, is there any other reason they can't be shut down for a weekend and re-started without issue on a Monday?

I realize I've typed a lot here but I'd really appreciate any help I can get. My main concern is time, as in I need to manage it so I have as little down-time as possible. I am asking these questions here because I've had no luck finding answers in any of the manuals or discussions I've read concerning these machines. If anyone has answers or a link to any material I can access that will help me, I'd appreciate it greatly. If you've read all this, thank you!

[Peter Apps]

It is usual practice to leave GCs on all the time. I suspect that this may be a tradition from the times when they were huge clunky things with crude temperature controls and mechanical gas controls that took ages to stabilize. The advantage of leaving them on is that they are ready to run more quickly and that septa and ferrules tend to leak more if their temperatures go up and down, the disadvantages are that they use a bit more gas and electricity and while they are on they are vulnerable to being destroyed by power spikes. My lab has been out of action for nearly a year because we don't have funds to fix the MS that was zapped by the neutral line being powered live form another phase (by my boss !!).

8 hours does sound like along time to stabilize, but it may be related to the adsorbent columns that are used for gas analyses. Specialists in that area will be able to advise.

Peter

[Rndirk]

What kind of detection are you using?

It all depends on the settings in your standy method. There have actually been a couple of topics here recently about that, you can do a forum search on "standby".

I think the general consensus is that shutting down a GC over the weekend is not worth it. The main reason is the loss of carrier gas flow, which makes a column catch dust, air and water. If you want to shut it down it's better to take the column and seal it, which you don't want to do on friday and install it again on monday.

[James_Ball]

FID and ECD detectors can stabilize from a cold start within a few hours, but if you are using a TCD, which is used a lot in gas analysis, it usually does take longer to stabilize thermally, and any shift in temperature will cause a shift in baseline on that detector.

If you are really worried about power consumption you could lower the oven temperature and cut the carrier flow by about 50% and you should be able to restart after a day without too much trouble, but dropping the detector temps will cause the largest problem with stability. Also the 3800 being an older model it won't be as quick to recover as some of the newer ones will.

If you don't have some high quality surge protection you definitely want to get it, as the equipment becomes older it will be more difficult to find replacement electronics, so protect them as much as you can. When we built our new building we had surge protectors installed in each breaker panel and huge ones on the incoming lines. In 12 years we have yet to lose something because of a surge, though if we were out of power for any extended time period we would go around and unplug equipment just to be safe, but now we have a 150kw backup generator and with the delay it gives when power is restored it takes care of the sudden spike that can happen at that time.

[jamesrh]

Wow. I greatly appreciate your responses, I didn't expect as much help as quickly as this.

We use a front TCD and a middle FID and yeah, the "boss" did say that shutting them down and stopping the carrier gas flow wasn't really a good thing, so there's that. He also talked about the way the columns should maintain a good temp so it didn't fluctuate and that makes sense with what some of you have mentioned.

I know that the "Standby" method drops the columns to a very low baseline temp and slows all the flows to a minimum, I think it's to the lowest levels recommended for the columns. I will go back and see if I can find the Standby discussions here though, I understand what a method does and how it controls the chromatographs but unfortunately I don't think I could confidently build or edit one at this time. Plus, these machines are going to be "overhauled and updated" soon so hopefully I'll be able to learn in the modern age and not the stone one.

As for "surge protection" we have some decent equipment in that area, we haven't had too many electrical problems where I'm at lately but being too careful is never a bad thing. When we upgrade I'm going to see if there's more we can do in that area as well.

I sincerely thank you all for your input and, if anyone else has any information I may be able to use, I'm open to all good suggestions!