Cannot achieve constant peak widths

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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Hello,

4 days ago I vented my Agilent 5975C MSD to clean the source and trim the GC column. Did the usual maintenance, changed the liner, reinstalled the column. I have alot of experience doing this and usually things go well.

I pumped down the instrument over the weekend and came in this morning to just tighten the inlet and MSD auxiliary nuts and noticed that everything seemed good, the turbo pump was at 100%, MSD status was "OK".

But, when I did the tune, in CI mode (NCI), I got the message "cannot achieve constant peak widths". I tried to tune a few more times, same problem. I checked the PFDTD level, and it was 1/8-1/4 full, so that's not the problem. I know that I connected all the wires correctly to the MSD source. The filament seems to be working because I can see thru the clear source's window that it lights up when attempting to tune. I also ran a Methane pre-tune in PCI mode to check for leaks and there is no peak at 32 m/z, the ratio of m/z 17 to 19 is 17 is much, much higher than 19, so showing that there is no air or water in the source.

On thing that concerns me is that in the diagnostics display it shows EMV = 0. Shouldn't it be 1100-1200? Is my filament broken? If so, why does it glow when tuning?

Any more troubleshooting ideas anyone might have? I would like to avoid venting the MSD, but it looks like I'm going to have to do it....sigh.

Update: a few hours later....I decided to vent the MSD and install the EI source. I pumped it down successfully then waited an hour over lunch for the vacuum to stabilize. I think ran an air/water leak check and got: 2.93% water, 0.38% O2, 1.84% CO2 and 55.43% N2/water. I think this does not indicate a serious leak? If it were a leak, I should be getting very high CO2/O2 values n'est ce pas?

Update2: I decided to check the CI source body and look more closely for any shorts that might be existing. Got out the ol' multimeter (MM), set it to continuity mode and started probing. Nothing. I even checked to see if the filament was continuous, yes indeedy it was. So, filament is ok, the source body is ok...what else could it be? I decided to run the EI tune again and see if there were any improvements over the last 25 mins, and I ran a Tune evaluation as well. The abundances were higher, and the H2O percent was down to 0.96%, so looks like the vacuum pump was doing it's job. But still, why the strange "cannot achieve constant peak widths" error when I tuned the MSD in CI mode this morning? I guess I'll just replace the CI filament and hope for the best, reinstall the CI source and pump it down overnight. I'll find out tomorrow morning how it went and I'll let you all know. I know you're all excited to find out what happened so I'll try to post the results early.

Update3: Sad news...tuned the CI MSD and same error as before: "cannot achieve constant peak widths". I thought I saw one fraction of a second where it started to form nice tuning peaks, but probably it was just wishful thinking and my mind was just manifesting what IT wanted to see. So I'm back to where I started....alone, out of ideas, with a broken MSD in NCI mode. *sigh*

Update4: So, I tried tuning it in PCI mode...that's positive chemical ionization for you folks out there that aren't familiar with chemical ionization. I actually successfully tuned, albeit not very easily, but it tuned. I then did a methane flow setup tune and that went fine. One weird thing was that the MSD had to ramp the methane flow from 20 to 40 to get the correct ion ratios for the PCI tune. Not sure why. I checked the methane gas tank and it was delivering 28 psi and still had 250 psi left in the tank. So that means the methane was still available. I then tried to tune in NCI mode again....but got that same error: "cannot achieve constant peak widths". I switched back to PCI, tuned again in PCI and now IT could not tune and gave the same error as NCI. At this point I'm running out of ideas. If anyone can help please do. My next troubleshooting step is to plug the MSD with a no-hole ferrule and try tuning it separated from the GC. Personally, I think this step is a waste of time...but it's worth a shot. What do I have to lose, right?
Normally that error indicates a problem with the mass filter electronics. If you put in the EI source and tune one day then let it set a day or two and see if the peak widths are the same by doing a manual tune profile mode. If the peak widths change significantly then there is some problem in the mass filter electronics. Could be it just needs the coils tuned or that the quads have become contaminated.

I have also seen problems if the hard wires surrounding the quads are touching, or near touching. Those can move if bumped when changing a source, so you may want to check those too.

The higher the pressure in the analyzer the more difficult it is to maintain the peak widths so could be why you are seeing the problem more with the CI source.
The past is there to guide us into the future, not to dwell in.
Yes, it does seem to be an electronics problem...because all the simple solutions have not worked. I was able to tune it in EI mode, but I didn't try it two days later, because I didn't have the time. My colleagues and I need this MSD up and running ASAP. I don't think there is a vacuum issue because the turbo reaches 100%, and I really feel that everything is tight. Also, I tested for air/water leaks with the EI source and they were insignificant. The MSD pumps down very fast. But that is interesting about the source's wires might be touching the quadrupole. I think they are far enough away, but I would have to check. I'll give an update on this probably later today or tomorrow.
Well, about 4 hours after I had vented the MSD and plugged it with a no-ferrule MSD nut, I started the CI setup for PCI mode. Once it got to the step where the MSD starts the fine adjustment of the methane flow (adjusting the CI 28/27 m/z ratio) to get a value of 2.2, it just could not achieve it. It would increase the flow: 40....41....42....43....44...etc, all the way up to 55 and I finally stopped it. I was able to run a PCI tune at the 55 flow rate (2 mL/min), but I didn't feel very confident that it would tune in NCI. Not with that flow. Plus the PCI tune Mass 598.6 was 0.16 and it should be higher than that. I switched to NCI mode, pressed the tune button and waited patiently with no expectations. I guess life just wasn't on my side this time, and I was back were I started 2 days ago: "cannot achieve constant peak widths".....
Well, I finally gave up and decided to call Agilent for a service call. We'll see how it goes and what they find out today. I suspect it's an electronics or wiring problem, probably with the CI source. I also think they will say that the MSD is working fine because I was able to tune in EI mode with the EI source. It can't be related to my maintenance on the GC side of things, because it couldn't tune even with the MSD isolated from the GC.

I'll keep you all up-to-date because I know you've been waking up early every morning just to read this blog forum to find out what the solution to this problem is! :lol:
The MSD technician came today and one of first things was to check the vacuum. The methane ionization gas was flowing at 30% and according to the Flow and Pressure Readings Table that should correspond to a vacuum pressure of 1.5x10^4 Torr. According to the vacuum gauge on the MSD that's exactly what it was. So this was indicating that the methane was getting into the MSD source and therefore probably wasn't the source of the problem. Also, we knew that methane gas was going into the source because the vacuum would drop from 10^-7 T to 10^-4 T.

Next we checked if the MSD was using a corrupt tune file. I was a little nervous about this because no one wants to pay $100/hr to a technician to just come in and copy + paste a new file and "problem solved"! They rebuilt a new tune file from scratch and tested it in PCI mode. Results: same problem, it couldn't stabilize the ion ratios and couldn't get constant peak widths. We tried adjusting the methane gas flow with the new file and it just kept creeping up the gas flow level to achieve the 2.2 ratio for the 28/27 ions needed for good PCI (needs to be between 1.5 and 5.0). In fact, the technician ran a test of 20 to 40 flow and the ion abundance of the key ions (m/z 28, 30) for methane were unstable.

This led the technician to suspect that maybe there is a problem with the reagent gas shutoff valve, the tuning calibrant valve or the purge valve. All these valves are in the line for when the tuning fluid (PFDTD) is being introduced into the source. Before changing each valve, which could introduce other problems later, we changed the electronics board that controls those valves. Just to make sure it wasn't an electronics issue.

When tuning, we could hear the *click* of valve opening and closing, even felt the faint, satisfying buzz of the valve's movement with our fingers....but maybe one of the valves wasn't opening enough? Maybe one is getting stuck or lazy? We had eliminated the reagent gas shutoff valve as being the issue, but what about the tuning calibrant valve?

This would make sense since the issue in the first place was: "cannot achieve constant peak widths". Meaning the tuning calibrant is not flowing into the source at a constant rate. Unfortunately, we didn't have an extra calibrant valve lying around, so we have to order one, replace it and see. Won't know until Wednesday.

In the meantime, just to eliminate the CI ion source as the problem, I switched it out with an extra one we had and pumped down the MSD and I will leave it over the weekend for the vacuum to stabilize.

Stay tuned for the results of the CI tune with the replacement source on Monday!
I did once have a 5971 with a bad cal valve. It would open and begin to tune, then over time it would slowly close and the signal would just fade away. That one took a while to diagnose for sure, since the valve would click very loudly, but the coil just would not hope it open.
The past is there to guide us into the future, not to dwell in.
Update: I tried to run a PCI methane flow setup with the substitute CI source. It was able to complete that task, but I could tell it didn't do it easily. Then I ran the PCI tune and it failed. It generated the error I'm now very familiar with - all together now: "Cannot achieve constant peak widths".

So, this confirms that the issue is a deeper issue and probably on Wednesday, when we switch the calibration valve this should solve the problem....I hope!
Update 8: Well, the new calibration valve didn't change anything. That really surprised me, and now I'm starting to run out of ideas...and out of options.

I tried one more time to tune in PCI mode using 25 and 30 flow of methane (ionization gas), but I still got the error: "cannot achieve constant peak widths."

Under the advice of the service technician, I've switched out the CI source to a clean EI source. I'm going to leave it on the weekend to pump down and then on Tuesday I'll bake out the column and tune it in EI mode. Apparently, the last tunes from the EI source didn't look too good, so maybe the quadrupole or the electron multiplier are faulty?

I wonder if one still keeps the MSD if its electron multiplier or quadrupole is faulty?
Update 9: Last week I cleaned the EI source and switched out the CI source. I pumped down the MSD over the weekend. This morning I baked out the system as per Agilent's site directions (https://bit.ly/3nOKU1e), set the column flow to 1.0 mL/min; split mode; split vent at 200 mL/min and left this for 10 mins. Then I started the bakeout with the oven at 325°C, front inlet at 300°C, source at 300°C, quadrupole at 200°C and left this for 30 mins. I then brought the everything back to our normal operating parameters and tuned it in EI. The tune was better than last week, but I feel it won't be good enough. I sent the pdf of the tune to the Agilent technician and I'll see what they say about it. I'm starting to suspect that our MSD may need replacement.
Hajime65 wrote:
Update 8: Well, the new calibration valve didn't change anything. That really surprised me, and now I'm starting to run out of ideas...and out of options.

I tried one more time to tune in PCI mode using 25 and 30 flow of methane (ionization gas), but I still got the error: "cannot achieve constant peak widths."

Under the advice of the service technician, I've switched out the CI source to a clean EI source. I'm going to leave it on the weekend to pump down and then on Tuesday I'll bake out the column and tune it in EI mode. Apparently, the last tunes from the EI source didn't look too good, so maybe the quadrupole or the electron multiplier are faulty?

I wonder if one still keeps the MSD if its electron multiplier or quadrupole is faulty?


The electron multiplier is a consumable item, they are replaceable and normally last a few years before needing to be replaced. What is the EM voltage when doing a tune in EI mode? If it is getting above 2000v it is getting old.

The actual quadrupole doesn't normally go bad, just the controller board, which is the board on the side plate that opens when you service the source. It feeds the RF and DC energy to the quads through the bare rigid wires that are on the outside of the quad housing in the vacuum chamber. Those wires can become bent or moved slightly and if something causes them to ground you will get a similar problem. Also is something of high molecular weight made it into the vacuum chamber and contaminated the quads it can cause a peak width problem. This is more rare, but it can happen. Heavy oils or waxes, or column stationary phase are the usual suspects when this happens. I have seen certain samples injected that literally strip the stationary phase from a capillary column and it ends up in the vacuum chamber. The quads can be cleaned. I have done it but it is not for the faint of heart, holding a piece of fused silica in your hands that cost about $10k if you drop it. Back when the quads were metal it was not so bad :)
The past is there to guide us into the future, not to dwell in.
Update 9: After nearly a month, we finally determined the problem.

When tuning the MSD in EI mode, the technician noticed that the voltages reported on the tune report were not within the normal parameters for parts of the ion source body, especially the ion focus lens. It was supposed to be 90V but it was around 45V. This led them to start checking the electrical connections between the ion source and the electronic computer board that controls each component. They knew what the expected voltages signals should be between each. There is a cable with multiple pins that connects the source wiring to the computer board. The computer sends signals thru this cable via the individual pins to the components of the ion source. We disconnected the cable and tested inputs and outputs of each pin....sure enough, ONE of the pins was not transmitting a signal! This one was the ion focus lens pin. We looked at the overall condition of the cable and it looks like it had been "kinked" when opening and closing the ion source door. To test if the cable was the issue, we "borrowed" a cable from a working MSD and then tuned the instrument.

It worked!!!

The repair technician ordered a new cable for us, and then installed it this week. Wow! What a difference in signal and the tunes are beautiful in EI and CI.

It looks like that cable was very slowly getting damaged, and the electronics were boosting the voltages and signals to compensate. When I did my maintenance and unplugged that cable, it was probably on its last legs and couldn't stand being bent out of shape again. It gave out, and when I put it back together, pumped down the machine and tried to tune, the cable could not conduct the signals necessary for the MSD to tune properly, it tried to compensate by raising voltages, but ultimately it failed and therefore giving the error:

"Cannot achieve constant peak widths".
James_Ball wrote:
Hajime65 wrote:
Update 8: Well, the new calibration valve didn't change anything. That really surprised me, and now I'm starting to run out of ideas...and out of options.

I tried one more time to tune in PCI mode using 25 and 30 flow of methane (ionization gas), but I still got the error: "cannot achieve constant peak widths."

Under the advice of the service technician, I've switched out the CI source to a clean EI source. I'm going to leave it on the weekend to pump down and then on Tuesday I'll bake out the column and tune it in EI mode. Apparently, the last tunes from the EI source didn't look too good, so maybe the quadrupole or the electron multiplier are faulty?

I wonder if one still keeps the MSD if its electron multiplier or quadrupole is faulty?


The electron multiplier is a consumable item, they are replaceable and normally last a few years before needing to be replaced. What is the EM voltage when doing a tune in EI mode? If it is getting above 2000v it is getting old.

The actual quadrupole doesn't normally go bad, just the controller board, which is the board on the side plate that opens when you service the source. It feeds the RF and DC energy to the quads through the bare rigid wires that are on the outside of the quad housing in the vacuum chamber. Those wires can become bent or moved slightly and if something causes them to ground you will get a similar problem. Also is something of high molecular weight made it into the vacuum chamber and contaminated the quads it can cause a peak width problem. This is more rare, but it can happen. Heavy oils or waxes, or column stationary phase are the usual suspects when this happens. I have seen certain samples injected that literally strip the stationary phase from a capillary column and it ends up in the vacuum chamber. The quads can be cleaned. I have done it but it is not for the faint of heart, holding a piece of fused silica in your hands that cost about $10k if you drop it. Back when the quads were metal it was not so bad :)


Thanks for the reply and for following my posts James!

Looks like you were on the right track when you mentioned that the controller board might have something to do with the problem It wasn't the case with the quad/analyzer controller or the analyzer itself. The service technician cleaned the quad before we discovered the cable issue. That was one of the troubleshooting steps they folllowed to eliminate analyzer contamination. They unscrewed the quadrupole from its chamber and then using wires, they dipped it 3 times into a large graduated cylinder filled with methanol and with a bundled Kimwipe at the bottom to hold the quad.

But, when all was replaced and the machine was pumped down, we still couldn't get it to tune, even in EI mode.
I had this error one time and eventually gave in and called an engineer in. They trimmed a little off the column and it worked again. I never understood that, but then again, I also wasn't the one who installed said column, haha.
mburleson wrote:
I had this error one time and eventually gave in and called an engineer in. They trimmed a little off the column and it worked again. I never understood that, but then again, I also wasn't the one who installed said column, haha.


The end of the column should only extend 1-2mm past the tip of the transfer line, much longer and it sits in the ion chamber of the source and interferes with the ionization of the analytes. The best way I found to get a good depth of installation was to place a column scoring wafer flat side against the end of the transfer line tip and slide the column in until it touches. Then remove the wafer and tighten the column interface nut. The little bit it moves the column inwards as you tighten will be 1mm or a little less and is perfect.
The past is there to guide us into the future, not to dwell in.
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