Mass Spectrometry Troubleshooting Guide

from Spectroscopy, June 1995,V.10,No.5
compiled by Ken Busch, David Bostwick, and Sarah Shealy

Return to sci.techniques.mass-spec


Vacuum SystemsSensitivity and ResolutionData Analysis

Vacuum Systems

Symptoms

Possible Cause

Suggestions

Base pressure increase
High vacuum pumps off
Check ion gauge trip
-filament burnt out?
-sagging filament shorts out?
-power supply failure?
Check cooling water flow
-Water filter clogged?
-Scale buildup in tubes
-Inlet water too hot?
Check diffusion pump heater
-Heater shorted or open?
-Heater reset tripped?
-Thermal cut-off tripped?
-Poor electrical connection?
Check rough pump operation
-Pump oil low? high?
-Need to ballast
-Need to change oil?
Virtual Leak
Reseat gaskets and seals last changed
-Correct size gaskets?
-Vacuum-compatible lubrication?
Bake out system
Actual Leak
Check gaskets last changed
-Source gaskets OK?
-Pump gaskets embrittled?
-Flanges evenly torqued?
Check hose clamps
-Have clamps cut through hose?
-Clamped hose still pliable
Check rotary/sliding seals for dirt
-Sample solutions filtered?
-Vacuum lock seals clean?
Check for gas-line leaks
-Line ferrules tight?
-Line ferrule too tight?
-Glass-to-metal seals OK?
Spectral contamination
Check for pump oil backstreaming
-Cold traps working?
-Source needs cleaning?
-GC bleeding?
-Source temperature high enough?

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Sensitivity and Resolution

Symptoms

Possible Cause

Suggestions

Loss of Sensitivity
Analyzer pressure too high
See suggestions above
Source filament misaligned
Pull source
-Electron hole clear?
-Filament aligned with electron hole?
-Using correct filament material?
Electron multiplier gain down
Check multiplier gain
-Conversion dynode clean?
-HV power supply operational?
-Preamplifier functional?
-Output electrical connection clean?
-Check x-ray shield alignment
-How old is that multiplier?
Ion source is dirty
Berate previous user
-Clean or bake out source
-Too much sample?
-Samples decomposing?
Narrow mass range scanned
Widen scanned mass range
Ions may be higher or lower in mass
Check expected mass defects
No Signal
No ion beam
Check isolation valve
-Completely open?
-Slits closed too far?
Check filament continuity
Check for ion lens voltages
Check accelerating voltage
-Polarity set?
-Power supply operational?
Check electron multiplier/detector
-Power supplies operational?
-Electrical connections tight?
Check data system
-Computer parameters set?
-ADC, thresholds correct?
Resolution low
Peak shape shows lift-off
Quadrupole rods dirty
-Ion burn at source end of rods?
-Rods in alignment?
Peak shape skewed
Sector slits misaligned
-Slits open/close smoothly?
-Slits in parallel alignment?
-Slits at proper width?
-Ion focus potentials centered?
Pressure too high
See suggestions above

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Data Analysis

Symptoms

Possible Cause

Suggestions

Calibration error
Incorrect calibration file
Check current calibration file
-Correct calibration compound?
-Current calibration file?
-Instrument drift over time?
-Correct mass range specified?
-Acquisition parameters identical?
High background ion intensity
Column bleed in GC-MS
Check masses for fit to siloxane series
-Lower temperature of GC oven
-Deactivate with silylating reagent
-Remove degraded length of GC column
-Use less solvent in sample injection
-Check age of column
-Sample carry-over?
-Contaminated ion source
GC peak broadening
Active sites/dead volume
Check interface between GC and MS
-Deactivation needed?
-Make-up gas flow correct?
-Syringe working?
-Septum leaking?
-Column broken inside ferrule?

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