****************************************************************************** From: "Kerry M. Peru" Date: Wed, 23 Oct 1996 08:11:54 -0500 Subject: CI problems Organization: * I would like any suggestions that would aid in correcting the following problem that I have been experiencing while trying to perform some CI work. I operate an Autospec Q and for some reason I am having difficulties with achieving a clean CI spectrum. Here are a list of the problems encountered and remedial actions taken to date: Upon introducing the CI gas (I have tried Ammonia, Methane and Isobutane) a large background is apparent ie: a peak at every mass with emphasis at the low end of the scan range (I am scanning from 60-500 daltons). I have tried a full range of the emission current settings and eV settings but the background is still abundant enough to mask the analytes of interest and create very poor apparent sensitivity. My source temperature is at the lowest it can maintain (130C) and the source is as tight as I can make it. I am definitely achieving CI conditions, as I have introduced known compounds at a concentration that I are visible and the M+1 ion is the most abundant. I have cleaned the CI source, changed ceramics, cleaned the source housing, leaked checked all lines, baked the source at 300C, but I still get this large background signal. I think it is some sort of contamination (likely hydrocarbon) but I do not know where it is coming from or how to get rid of it. I ruled out contaminated CI gases, as I mentioned previously, 3 different gases were used. A direct e-mail to me at PeruK@nhrisv.nhrc.sk.doe.ca of any suggestions would be greatly appreciated. Kerry M. Peru National Hydrology Research Centre Environment Canada 11-Innovation Blvd., Saskatoon, Sk., S7N 3H5 ph: 306-975-4206 Fax: 306-975-5143 ****************************************************************************** From: John Barton Date: Fri, 25 Oct 1996 12:56:04 +0000 Subject: Re: CI problems Organization: Imperial College I also have an AutoSpec-Q, and do a lot (2000 samples/year) of C.I. using ammonia as a reagent gas, so I have some observations which may help. There are usually quite a few background peaks, but these are of low intensity and are always swamped by analyte peaks if the source is working efficiently in C.I. mode. Try introducing ~ 2 microlitres of amyl actetate into the septum reservoir, and use ammonia as the reagent gas. Set the ammonia pressure in the source housing to about 5e-5 mbar, and tune to optimise the peak at m/z 148 (M+NH4). If things are going right, this peak should be at least a factor of 20 higher than the peak at m/z 70. In fact, I find that m/z 70 is barely detectable, and the 148 peak is off scale with the multiplier at 220 volts. If no amount of tuning helps, then check the seal between the solids probe and the source block. A chip out of the probe tip ceramic will cause considerable gas leakage. Also check the seal between the reentrant and the spring-loaded sliding tube which mates with it. I once found that someone had fitted a weaker spring to this tube, which was enough to degrade the CI performance through leakage. You do not say what type of solids probe you have. The water-cooled probe has a two-piece ceramic tip. Part of this tip is made of machinable ceramic (macor), and part out of boron nitride. These materials can absorb certain chemicals, which then bleed out over a long period of time. Try baking the probe at its highest temperature, or replace the ceramic tip. If you replace it, it will still need baking, as the macor absorbs CO2 and the boron nitride absorbs water in the atmosphere. One possible source of contamination is the tubing used to connect the gas bottles to the instrument. Make sure all the tubing is GC-grade stainless steel, and all valves are also stainless steel, and preferably packless. I hope you find these comments useful Good luck! John Barton Chemistry Dept, Imperial College, LONDON, UK ****************************************************************************** ****************************************************************************** From: Bill Cotham Date: Mon, 28 Oct 1996 09:26:19 -0500 Subject: Re: CI problems Organization: USC Mass Spectrometry Center Just a quick comment about the ceraminc probe tips. John is right about the two piece tips causing some problems. We have switched to a one piece tip made by SIS which works much better. Usually no baking or degassing required at all. I also concur on his comments about CI. With no analyte, you will almost always see the low mass "grass" in a CI spectrum. -- Bill Cotham, Ph.D. Mass Spectrometry Laboratory Dept. of Chemistry and Biochemistry University of South Carolina Columbia, SC 29208 803-777-2039 (voice) 803-777-9521 (fax) ****************************************************************************** From: mrdio007@aol.com (MrDio007) Date: 4 Nov 1996 23:54:09 -0500 Subject: Re: CI problems Organization: America Online, Inc. (1-800-827-6364) I have had this problem and believed myself to have resolved it by changing the plumbing in (and leading up to) the instrument. Sources of contamination include; Vac Pump oil: Rough pumps frequently oil surfaces around them and this is usually the same place where the CI gas enters the instrument. And where unused regulators and connectors sit exposed to oil mists. Note that there is an environmental issue attendent in the discovery of this oil. "Bad" tanks of gas; we blamed isobutane once as it usually is supplied (or used) at lower purities than are recommended by instrument manufacturers for use in CI. Regulators: never blamed one yet Contaminated tubing: seen this one following switching an instrment from ESI to CI. Put new copper tubing on and it got better. I have thought that contamination tends to move further along (spreads) with time. This has led me to want to cap these gas inlets and outlets when not in use. Poppet Failure: The little solenoids or valves can some times bleed lubricant into the system and contaminate the gas lines. I'd try to determine the first moment that you noticed the contamination and then make a list of what changed. Then reconfigure it in the intial state (or the state in which it last worked) and try it. I have used a Finnigan XSQ intrument which allows one to directly connect the instruments rough pump draw to the CI line to flush it. Leaving the ion source hot, the manafold warm and letting the pump pull on the lines has seemed to clean things up on occaision. You might try using methane for trouble shooting as it is usually cleaner. Remember that it may be difficult to ascertain that you have fixed the problem as the contamination may remain after the "source" has been removed. This speaks to using long "wait" periods after a change to see if some improvement has been made, however slight. It may be a case of step-wise improvement towards your orignal "spec". Good luck these are frustrating at times. matt sweeney ******************************************************************************