Designing the ideal standby method

Hello all

 

I'm looking at designing some standby methods for my 4 GC-FIDs and 3 GC-MSs as they are often sitting idle for 3/4 days a week and are happily consuming helium, hydrogen and generally sucking money away basically for no reason. Turning them off/on is not an option as we often need some of them fairly urgently, so I thought a 'Standby' method would be the best way to conserve!

 

I just want some advice on the key things to be looking at regulating. From scrawling this and other forums I've pieced together the following information so if anybody spots any glaring holes, please let me know

 

Oven temperature: Low (30-50)

Column: Carrier gases set to a minimum flow (~0.5ml?) to protect column and/or MS (we are an oils lab so use non-polar columns)

FID: Keep at around 100 to prevent moisture forming on jet. Turn off all gases except for carrier gas

MS: Keep at temperature to ensure no build up of moisture/solvent anything on source etc. Same with aux line?

 

My main point of concern is the inlet. We have split and splitless injectors - how much flow do we need to keep going for the split flow? Any? Low? I've seen some people say to set the method to splitless and put a low flow on it (1-2ml/min). Currently it's on Gas Saver running 20ml/min which I feel is fairly high compared to the remainder of the system.

 

Any advice on this will be appreciated!

  • Hi ryanedwardson,

    The idea to create a standby method is a good one. Many instrument users do this successfully, but many others create methods that shorten column life and end up costing more money in the long run. The idea of a standby method is to keep the system healthy and able to perform at a moments notice. All points that you outlined. I have been a service rep since the late 1980's and some of what I will suggest here will cause debate for those that are able to create methods that are below factory spec and seemingly have no issues.

    Taking your points:

    Oven temperature: Low (30-50) ( My suggestion, stay at the main method starting temperature)

     

    Column: Carrier gases set to a minimum flow (~0.5ml?) to protect column and/or MS (we are an oils lab so use non-polar columns) (Reducing column flow in some cases with reduced oven temperature can leave the column with not enough flow and head pressure to keep a column healthy and prevent air infiltration through the split vent. You are only saving 0.5ml/min typically here anyway so its not worth it)

     

    FID: Keep at around 100 to prevent moisture forming on jet. Turn off all gases except for carrier gas (Gases off, but keep the temperature up to eliminate any siloxane build up from the column. 150c or higher. Higher temperature costs nothing, moisture should not be an issue anyway with proper gas purity and filters)

    MS: Keep at temperature to ensure no build up of moisture/solvent anything on source etc. Same with aux line?( Yes)

     

    The Inlet should maintain proper total flow to maintain its operation, this is why Agilent/HP came up with the gas saver feature. The older instruments such as the 5890 just had a total flow knob and usually it wasn't adjusted for times when the instrument was idle and used more gas. Gas saver also kicks in at a defined time , such as 2 minutes, as high flow is really only needed at injection. This next statement may cause the most discussion. Leave the total inlet flow at 20ml/min in gas saver, you could try and reduce it to something like 15ml/min (below factory specs) , but keep in mind we want to maintain head pressure and avoid any air entering the inlet through the split vent which is detrimental to the column. In short, you have a modern instrument  with saving features already there, Gas saver, EPC detector flow for FID gases can be off with the simple load of a standby method. I hope this helps.

     

     

     

    Regards

    James

  • Thanks very much James - great advice.

     

    I knew I was on the right track, but like you said there's a line there between savings and causing damage to your instrument which ends up costing you more!

     

    I'll keep the inlet going at 20ml/min, I feel like that's where most of the problems can start.

     

    For the FID, we use Hydrogen, Comp Air and Helium. Helium is also our column carrier gas - can I switch off the 'extra' helium supply and just leave the carrier gas running to it. Is that sufficient? Or am I better keeping a supply going but reduce the amount - currently they run about 40ml/min which is quite high in my view!

     

    Thanks again

    Ryan

  • Thanks James - It certainly is very high, this part of the reason my attention has been drawn to our He consumption in the first place. I've come into the dept. recently and am looking into everything to determine what can/can't be standardised.

     

    Many thanks for all your assistance on this - time to get to work!

  • The helium make up gas can be turned off for the detector along with all the other detector support gases. 40ml/min is quite high for make up gas. 

    Regards

    James

  • Hello Ryan, Over the many years of working with Agilent GC's & GCMS's, I have developed a true gas saver / stand by method. Please contact me directly at my Agilent email larry.garretson@agilent.com so that we may discuss in greater detail. If you choose to implement my approach we can re-post the details on this forum. Best regards, Larry Garretson, Senior Applications Chemist

  • Have you considered gas generators for Air, H2 and N2?

    Helium could be substituted by H2 as a carrier and, from what I read, this allows for faster analysis.

    The danger is H2 accumulation in oven (broken column) or MSD (stopped pump).

     

    What do you think ?

    Would there be much saving this way?

  • Hi csiquet_fles2000,

    Generators are a viable solution as long as they are well maintained. The switch on the carrier gas side is not straight forward as there are method and column changes that will be needed in most cases. One reference is below:

    Converting EI GC/MSD to Hydrogen 

     

    For anyone considering the change to H2, it is always good to reach out to your local support and review your instrument configuration to make sure the change is applicable to your hardware. For example H2 would not be appropriate with a purge and trap system or headspace. There are alternate solutions in each case. Agilent contact centers can provide information on applications as well as safety information.

    Regards

    James

  • Hi James,

        I have the same question as Ryan. To try to save Helium(we are very small company with tight budget), I set up an standby method with all heat source set into 35C(inlet, oven, aux line, MS EIXTR ion source with 0.5ml He flow. As covid restriction, we only turn up and run GCMS when we need to, usually quite urgent just like ryan said. Our GCMS is 7890-5077MSD, with HP 5MS UI column, split (20:1) with gas saver on 15ml after 3 min.

    When I finished the run, I put on this standby method, and the flow set into 0.5ml while the MS source gradually lowered its temperature. Our method starting temp is 40C.

     

    I am wondering, have I already damage the column?

     This is one of the standard that I run once a month. I prepared a bulk calibration level 1 solution and split into multiple GC vial and put them in frozen, Ambient, chill. The frozen one run as calibration solution while Ambient and chill run as a sample. In the chromatograph, the peak showing RT shift and peak broadening every month. They are all come from one preparation and divided into multiple GC vials and store in different temperature. The rest of the other standard behave the same. The tune report passed every time before I run the GC and although I use this standby method, the moisture content maximum was only 5.8% as I put it up back to our method for 1 hour before I run the standard(column flow 1ml, split 20:1, start with 40C oven, 230C inlet, Aux line, ion source, 150C quad).

     

    Although the peak elute later every month and symmetry >2 eventually, as the calibration behave the same, the accuracy was not degraded.

     

    I also have issue that on daily basis with other sample since last year, RT shift later days by days when running sample. it only shift back earlier after trimming column. On the above chromatogram, the method already applied retention time lock with its internal standard. It seems to me the compound spend more time in the column?

     

    I have contacted Agilent customer service but still haven't had any answer yet.

     

    So I am just wondering, if anyone, could contribute their thought here? I will be much much appreciate all advice.

     

    Thank you

     

    Candy

  • Hi candy,

    Thank you for the post and the great detail. Column damage is difficult to determine. Is it damage or natural age from use, hard to tell. Columns do have a lifespan depending on gas quality, use and proper storage and care. For a standby method, I wouldn't reduce any of my MSD heated zones and would suggest leaving them at temperature. This helps keep the source not only ready to run, but aids in keeping it cleaner. 

     

    For column flow, reducing to 0.5ml/min from 1ml/min wouldn't really show a cost benefit as its such a small change. I would suggest leaving the flow at the usual operating flow of 1ml/min. Changing to 0.5ml/min will only save you about 720ml of He per day.  Over the lifespan of a He tank this will give you a couple of more days of He usage at the possible sacrifice of column life.

     

    Below, some rough math that I think will help, hopefully I haven't made any errors here, its early and I havent started coffee yet  :

     

    A regular, common size gas cylinder( North America)  UHP grade (0.999995% pure) filled under standard temperature and atmospheric conditions will hold approximately  291 cubic feet of helium at 2500 PSI. This equates to 8240 cubic liters of gas.

     

    A split/splitless inlet in standby only with gas saver on will have a flow of 24ml/min approx. ( 20ml/min gas saver, 3ml/min septum purge, 1 ml/min column flow).  

     

    Typical inlet usage 0.024 liters X 60 minutes= 1.44 liters per hour or 34.56 liters per day for one inlet.

    8240/34.56 = 238.42 Days. 

     

    One inlet in standby from filled tank to depleted tank should go 238 days. In practice, you should never drain a tank below a couple of hundred PSI, so practical terms 230 days would be a good round number per inlet.

     

    Regards

    James

  • Hi James,

     

         Thank you for replying so swiftly. I am too silly thought that I could use 1 Helium gas cylinder for more than 1 year. As the covid lock down, the lab was shut for a couple of months, the GCMS wasn't use much for the year. The GC consumable and standard could save apart form the Helium. Thank you for the calculation. I might consider Hydrogen generator if possible for my method, a bit of research and method development for the next year. Thank you every one here. I have learnt a lot that couldn't be learnt in any courses or books

     

    Thanks

     

    Candy

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