Chromatography Forum

My instruments is GOW-MAC 600 with DID(discharge Ionisation Detector),and columns type is Hayesep Q, when we run Calibartion Gas (He balance,contain:H2,Ar,N2 , CO,CO2,CH4 ), all the testing result is quite good and repeatable and reproduciable, but when test NH3, The results is not so good and baseline a little bit noisy and fluctuation and RT of CO2 a little bit later, after running a couple of sample of NH3 ,then test STDGAS again, all the result turn small ,and in succession run stdgas ,the result increase by degree till to original value, I think maybe due to property of NH3 with high boilling point.
I am looking forward some expertise and explaination for this
thanks in advance

Lindeccl,

Please recognize I have a significant bias in this case as I make a competitive detector. Assuming you have reasonable peak shape, I would suggest that your issue with noisy baseline and loss of sensitivity is due to your detector rather than due to your column. I believe what may be happening is that ammonia is getting up into the discharge region of the two electrodes and altering the discharge dynamics. Ammonia on a discharging metal electrode has a significant potential for a reaction which affects the character of the electrode.

If you want to test the theory, there are lots of things to try. Inject just one ammonia sample, bake the column, and see if the helium standard is still depressed. Try increasing the reaction gas flow to suppress the ammonia from getting into the discharge chamber. You may cut into the sensitivity if you do this although my experience has been that increased flow does not have that significant an effect on sensitivity. You might also try shooting less to prevent the ammonia from getting to the discharge but this comes at the price of detection limit.

On a more complicated scale, you could try a vent valve (a 3 way T with an on/off valve or a 4 way rotary valve if your GC has room) to eliminate the bulk of the ammonia while maintaining loop size for sensitivity. I would only go to this if you find it is the detector.

Finally, an alternative column which I have seen used very effectively for low level ammonia (low ppm) and is noted for high level ammonia in the HayeSep guide is an HayeSep P (8' X 1/8", 60/80 mesh.)

Best regards.

Thanks ACIMM
Thanks for yr reply, it seems that yr have lots of Experience about Detectors, we hope we could be friend and help each other, for properly resolve my issues , i like to give u details about my issues , yr know , when we run NH3 sample, we use the VICI ten ports valve backflush ,the means while NH3 via the first pre-columns have been backflush and never get into DID unless the valve leakage,otherwise need a long time to bake out and spend a long time to allow the DID to be stable , it seems that it is not case ,the valve work properly,our impurities in NH3 is PPM even PPB level ,quite lower, Our product is 6.0N NH3. Have you produced DID,if so ,could you give some infor about this , thanks a lot

another issues is about H2 , our carrier gas is 6.0N He , When we run He(6.0N) with the sample method , only the H2 get negative peak , while run Calibration Gas get normal , the supplier told us maybe due to the difference of the purity , i dont think So , we have many GC,why just have this issues , according the theory , as long as exist the difference of pruity ,THE DID generate negative peak ,and more strange negative degree is different ,and some N2 also have the same issues after baking DID, Could you help me to figure out the problem .

Thanks a million

LDCCL,

Feel free to contact me though my web site which is listed under my profile below. Yes, I make a DID detector, both helium mode and argon mode capable.

If you back flush your ammonia I am not sure what would cause noise problems with your DID but I am perfectly willing to discuss this with you. One thing that does come to mind is rotor composition and possibility for wear and leakage.

Regarding negative peak for hydrogen, my first guess is level of neon in the Helium you are using (long story...) Hard to detect with a DID, almost certainly present, and according to a long-time user of my detector and other DID detectors, certainly has an effect.

Best regards.

Thanks ACIMM
yes explainatio is quite pretty, you must be a expert with detector, i am so luck to meet you .
you guss maybe my he present alittle neon, i dont know whether exist because i have no good way to test how much neon in our carrier gas , but another issues, after we incresing voltage of DID so as to remove the deposit in electrode for a couple of hours ,normally we kept the voltage in 500v , we increase 700 then decrese to normal, another stange is come out ,N2 also generate negative peak , i dont understand, normally when we run he carrier gas with a specific method, only H2 ,Can you tell me the other possibility exist or present .
Thanks a millions