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Amplified DNA Product Separation for Forensic Analysts

Troubleshooting

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Troubleshooting Guide

IssuePossible CauseAction
Poor mobility and reproducibilityTemperature fluctuation
  • Check instrument oven
  • Check environment temperature
Blocked, dirty capillaryChange capillary
Sample-wall interactionRinse capillary with polymer
Ion depletion of buffersReplace buffers
Buffer siphoningBuffer reservoir levels not equalEqualize buffer levels
Poor sensitivityNot enough amplified product in sampleReamplify or add more amplified product
Bubble in sample tube, capillary exposed to bubbleReinject
Poor laser powerService call, possible laser replacement
Ion competition during electrokinetic injection
  • Check quality of formamide
  • Compare results of sample to positive control included in kit - if okay, then evaluate extraction and sample preparation
Poor matrixRerun matrix
Gradual change in currentDifferent cathode/anode buffers and/or concentrationConfirm buffers
Current fluctuationsBubbles in the systemConduct a visual check for bubbles and clear by flushing with fresh polymer.
No currentPlugged capillary
  • Flush with polymer
  • Replace capillary
Wrong bufferConfirm buffers
Noisy baselinePoor matrixRerun matrix
Flat baselineCapillary not aligned in detector windowRealign capillary
No voltage
  • Confirm voltage settings
  • Ensure capillary ends are immersed in buffer
Sample not injected

Confirm the following:

  • Sample in vial
  • Sample is thoroughly mixed with formamide and is not on the side of the tube
  • Capillary end in sample solution
  • Injection time
Laser not functioningService call, possible laser replacement
Clogged capillary
  • Replenish with fresh polymer
  • Replace capillary
Electrical arcingBuffer spill in high voltage areasClean autosampler tray with distilled water and wipe dry
Poor peak shape

Incorrect current causes:

peak distortion

tailing [low current]

Replace buffer
Capillary failure
  • Replenish capillary with fresh polymer
  • Replace capillary

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