Peak shape problems

The sample was dissolved or diluted in a solvent with higher transmittance than the mobile phase at the chosen wavelength. The solvent is not clean or of poor quality. 

The sample is excited by the monochromatic light and emits fluorescence light  

Especially in the case of double peaks, the problem usually comes from a poor column. It must be replaced. 

The main causes are worn rotor seals, poor capillary fittings and capillaries with too large an inner diameter. 

Detector cell with too large an internal volume  

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Table 1 Peak shape problems and remedies Peak shape...

Figure 8.20. Three comparative chromatograms of three different bonded-phase columns using the optimized mobile phase conditions shown in Figure 8.15. The surprise finding of peak shape problems with two specific impurities might be attributed to the higher silanophilic activity of the column. Data presented in parts at Eastern Analytical Symposium, Somerset, New Jersey, November 2003.

Troubleshooting of Column Problems 17.2.1 Peak-Shape Problems... 

Extraeobum Effects Extracolumn effects are a more significant source of peak-shape problems than most people think. As a matter of fact, there is barely a chromatogram in the world that is free from extracolumn effects, but we have come to accept them as part of the reality of chromatography. Only when these effects become excessive do we attempt to reduce them. Also, extracolumn effects may cause problems when method are transferred from one instrument to another or from a standard column to a microbore column. 

In this section we will learn to diagnose and eliminate common chromatography problems. They are not necessarily column problems quite often the cause of a supposed column problem might be an incorrect setting of an instrumental parameter, or it may be related to the sample. For example, most peak-shape problems are not column problems. 

We divided this section into two major subsections peak-shape problems and retention-time problems. The last section then covers problems that do not fit into the first two categories, such as pressure problems. This structure should allow you to quickly move to the chapter that covers the problem that you are trying to solve. In the section of peak-shape problems, example chromatograms should also help to point you to the most appropriate section. While this structure is good for rapid troubleshooting, it also makes repetition unavoidable. Therefore, we would like to remind the reader that this part of the book is not designed to be read as a consecutive text. 

Peak-shape problems represent the most common problems in HPLC. In many cases, the chromatographer has come to accept less-than-perfect peak shape, as long as the peak distortion is not excessive. But distorted peaks are causes for integration problems, and are a sign that the best column performance is not reached. 

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