Diagnosing 'bad' chromatograms



Abstract Some basic troubleshooting. This chapter describes a number commonly occurring chromatograms where peaks show unexpected behaviour: compounds elute earlier, later, together, no peaks show up or other effects. The examples will help you to diagnose your chromatogram as well as to verify your hypotheses of the possible causes.


LevelBasic

 

Decrease in Retention time

Retention has decreasedRetention has decreased

List four (or five if you can) possible causes for this problem

How would you verify the suspected cause for this problem?

Increase in Retention time

Retention has increasedRetention has increased

List four (or five if you can) possible causes for this problem

How would you verify the suspected cause for this problem?

Excessively short Retention times

Short Retention timesShort Retention times

List four (or five if you can) possible causes for this problem

How would you verify the suspected cause for this problem?

No resolution

No separation takes placeNo separation takes place

List two possible causes for this problem.

Poor resolution

Peaks are overlappingPeaks are overlapping

List the possible causes for this problem

Rank in proper order which you would do first. Basic factors are :

  • Ease of operation
  • Probability that this is the problem

Distortion of peak shape

Peak is "tailing"Peak is

List four possible causes for this problem

Describe how you would verify (in the lab) each possible cause

Peak splitting

Peak gets "shoulders" or is splittingPeak gets

List possible causes for this problem 

Describe how you would verify (in the lab) each possible cause

Distortion of peak shape

Peak is "fronting" Peak is

List 2 possible causes for this problem

Describe how you would verify (in the lab) each possible cause

No flow through column

 

 No signal at allNo signal at all

List six possible causes for this problem  

Describe how you would verify (in the lab) each possible cause

Ghost peaks

Unexpected peaks show upUnexpected peaks show up

List three possible causes for this problem

Describe how you would verify (in the lab) each possible cause.

Noisy baseline

 

Example 1: no sampleExample 1: no sample

List possible causes for this problem above (example 1).

Example 2: very fast peaksExample 2: very fast peaks

Possible cause?

 

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