Q-Tof micro troubleshooting

Introduction

Two lists: standard (and special) procedures, and problems we've encountered (and how to deal with them). Contact Scott or Ori if you've discovered a new problem.

Procedures

Pressurization of the source
Booking any of the mass spectrometers online (external page )
A simple MS user guide ()

Problems

Scope stopped working properly
Instrument fails to achieve vacuum
Leaking / no spray / syringe plunger difficult to depress
Source and desolvation temperatures are slow to respond to changes
Lifetime of vulnerable parts
Isotope pattern matching poor
Plunger pushed out of syringe
Calibration wildly off
Full spectrum range not being acquired
Collision gas readout unstable
Capillary sparking
No signal in negative ion mode (positive works)
No response from capillary or cone voltage (stuck at 0)

Procedures

1. Pressurization of the source

With the mass spectrometer in standby mode, replace the regular glass source housing with the plastic housing that has been modified with a pressure gauge. Be sure to reconnect everything.
Attach the nitrogen line to the plastic housing via one of the available ports. (The nitrogen line you’re looking for is connected to the pressure meter built into the desk. ‘Gas 1’)
Set the cone gas and desolvation gas to normal operating values, then increase the external nitrogen flow into the source until the pressure gauge reads +4 in. H2O.
Flush the source in this manner for at least 10 min.
Adjust the external nitrogen flow so that the pressure gauge reads a positive pressure of 1 in. H2O.
You are now ready to run your sample. If you still see evidence of the presence of oxygen, return to flushing the source with N2.
After you’ve finished running your sample, there are two states in which the source can be left:
i) Turn the external nitrogen off, turn the instrument to standby and replace the regular source housing,
ii) OR, Increase the pressure back to 4 in. H2O then disconnect the waste line and in its place put a white plug. This will maintain the oxygen-free atmosphere overnight. To insert the plug you will have to simultaneously reduce the flow of nitrogen so that too much of an over pressure is not generated. Once the plug is in place adjust the nitrogen flow so that just a slight overpressure is maintained.

(Krista Vikse)

Problems

1. Problems with the scope on MassLynx, it has suddenly stopped working, responding to changes in settings, etc. The instrument is running fine because when can acquire a spectrum as normal, and in MCA format the scope operates normally. However, on terminating the acquisition the scope freezes with the last spectrum on display.
The problem may be a corrupted "peak config" file - so close Masslynx, and look in C:/temp for a file called peak config.dat. If it's not in the C:/temp directory, try a search. When you find it, delete it (or if you prefer, rename it to (i.e. oldpeak config.dat), then restart Masslynx (this file is recreated if not already present each time MassLynx is launched).
(Brian Fowler)

2. Instrument fails to achieve vacuum on pumping down after venting (amber light on).
Check the vacuum gauges. The green light will replace amber if the Tof Penning gauge drops below 2 × 10^-6 mbar. If the gauge reads e.g. 6 × 10^-9 mbar, it is malfunctioning. Try switching the collision gas on and off to provide a minor “jolt” to try and startle it back into life. If this doesn’t work, remove the cover by removing the three screws on the back top edge of the machine (only part way, so the inside of the instrument may be accessed from the back). Check that it is the gauge that is malfunctioning by swapping the Tof and Analyser cables and looking at the gauge readbacks – the readings should have swapped. Remove the cable from the Tof Penning gauge (large red cylinder), and turn the gauge head a quarter turn and remove. Tap the protruding metal probe with a screwdriver handle; this vibration may free buildup of deposits inside the gauge. If this doesn’t work, vent the instrument and remove gauge entirely at the first O-ring clamp, and install a replacement. Pump the instrument back down; this ought to fix the problem.
Clean the offending gauge according to the manufacturer’s instructions, and check the spark gap (should be 0.25 mm).
(Waters Help Line, 320626)

Addendum: if you reassemble the source after cleaning, and there is a loud hissing, and the MS not only fails to achieve vacuum but gives up after a couple of minutes, you've misplaced an O-ring. Reassemble the source correctly!
(Matt Henderson)

3. Leaking upon sample infusion / no spray / syringe plunger difficult or impossible to depress.
Tighten the PEEK fittings, try infusing sample again manually. If it is difficult or impossible to depress the plunger, there is a blockage. Remove the PEEK fitting at the probe, and try to infuse again. If the solution exits the PEEK tubing freely, the blockage is in the stainless steel capillary inside the inlet; clean according to the manual. If the solution does not exit the tubing, the blockage is in the PEEK tubing. Reverse; this will usually clear the blockage. If not, trim the PEEK tubing using a sharp knife (remove say 5 mm from the end originally nearest the syringe).
(Scott McIndoe)

4. Source and desolvation temperatures are slow to respond to changes.
The source T always responds slowly; be patient. Desolvation T should be fast. The system can sometimes be shocked into responding by setting the T much higher than that desired, then when the readback hits the desired level, reset it to that value. Check that the value holds. Tech Support suggest putting the machine into standby, closing MassLynx, switching off the electronics at the back of the instrument for 5 seconds (don’t leave off for >20 seconds or the machine will vent), rebooting the embedded PC, waiting 2 minutes, restarting MassLynx then back into action.
This did seem to improve the response. However, response did not kick in for either source or desolvation T until 150°C, at which point response was accurate. Changing the gas flow rate speeds up the rate of change in desolvation gas T.
(Waters Help Line, 322601)

5. Lifetime of vulnerable parts
Lifetime of turbomolecular pumps and MCP both about 2-4 years on average. Cost of replacement: about $12,000 for turbos, $6,000 for MCP. Also: engineers advise that roughing pump can cause more problems than turbos (about $4000).
(Bob Harrison)

6. Isotope pattern matching poor, especially re: the lower intensity peaks in the pattern. Related to this problem: appearance of strange ghost peaks that appear even when the MCP is reduced to 0 V.
The ghost peaks are an artifact from the pusher. The pulse width setting is usually 9 ms; try lowering to 7 or 8 ms to try and eliminate this. The TDC settings (access from the Tune page) can be altered to improve isotope pattern matching; in particular the Stop setting. Most of the thresholds are set to try and eliminate noise, but can be usefully set to 0 especially when getting patterns for low intensity ions.
A further note on isotope pattern matching. If your ion current is very strong, you will inevitably get poor pattern matching and mass accuracy will also be compromised. This may be solved by diluting your sample or detuning the position of the spray capillary (wind it away from the cone using the black dial on the far side of the source. NOTE! Return the spray head to the tuned position after detuning!
(Waters Help Line, 342461)

Addendum: the main cause of isotope pattern mismatching is actually degradation of the MCP detector. During the performance maintenance kit installation, we found that the MCP voltage had to be increased to 2700 V to maintain the same performance as was previously obtained...
(Brian Fowler)

7. System was working fine, but when the syringe was removed from the syringe pump, gas pressure forced the plunger back and out of the barrel, expelling the contents. Solvent could still however be forced through as usual, and the spray appeared normal. If the API gas was turned off and an empty syringe attached, nothing happened, then as soon as the API gas was turned on, gas pressure started to force the plunger out. Turning off the API gas immediately stopped this (so it seemed as if the vent behind the baffle was not plugged).
The probe was removed and the plastic ferrule/steel retainer/capillary assembly was removed and clean solvent passed through the system - solvent could be seen coming out from both the tip of the capillary and partway along. Replacing stainless steel capillary solved problem.
(Evan Crawford)

8. Calibration wildly off after changing ionisation modes or between projects.
Check that L_teff is the same for everyone. If you collect data using a different value from that which the machine was calibrated for, your data will be badly wrong.
(Brian Fowler)

9. When "Acquiring" a spectra, or even just observing a sample in the tune page, sometimes the m/z range does not go as high as the settings dictate. For example if the m/z range is set to acquire between 50 and 3000, sometimes only up to 2100 m/z will be collected, and nothing at all will appear between 2100 and 3000 (not even noise).
Click on the TOF tab. Near the bottom, just above the MCP voltage, there is an option for a "Manual Pusher" with a little white box beside it. Make sure this option is NOT checked. If it is not checked, the m/z range should go as high as specified; if it is checked the m/z range will be problematic.
(Matt Henderson)

10. When checking the Analyser Penning gauge or the gas cell dial on the front of the instrument, the readout continuously decreases.
This will generally be seen after adjusting the gas cell dial on the instrument. When the dial is pulled outward (to unlock it) there is usually a quick increase in the gas pressure. This can give a misleading reading after the adjustment and take a long time to drop to the actual setting. To get a more accurate result, click the collision gas button off for a few seconds and back on. Allow 10-20 minutes for the reading to stabilize.
(Jen Pape)

11. Small blue sparking can be noticed at the end of capillary, it will not disappear if you inject different solvents or air (turn off the room light to see the effect more clearly).
This plasma discharge is caused by a microscopically sharp point on the end of the capillary. Change the capillary or use sand paper to gently polish the capillary, by polishing the capillary, put the sand paper 90 degree against capillary to make sure the end of capillary flat.
(Jingwei Luo)

12. The signal in negative mode disappears within 5 minutes, and there is no signal if you change solution to NaI. But if machine is set to positive mode, the signal goes back to normal.
Solved by polishing the rusty adapter nut. Check MicroMass Z-spray API Source User’s Guide page 78 for this component.
(Jingwei Luo)

13. No response from either the capillary or cone voltage (both stuck at 0.
This is a problem with the safety interlock, and most often happens when swapping between different glass source housings. Remove the glass cylinder and make sure the small knob near the back screw was aligned and depressed when the probe casing was replaced. The knob position can be adjusted with a screw driver.
(Jessamyn Logan)