While performing HPLC experiment, needed data are retention time. I'm wondering if there is an influence of peak shape (bad or good) to the retention time.
in other words, do I need a good peak shape to confirm the retention time of analytes ?
You appear to be confusing the terms and relationships of some of the fundamental chromatography terms. As its name implies, peak shape is related to the whole shape of the peak seen on the chromatogram. The shape seen may be affected by such things as: the sample's chemistry, injection solvent used, concentration and how it reacts to the column chemistry and/or mobile phase. For example: If it is poorly ionized or not fully dissolved, then it may exhibit a non-Gaussian shape. If the sample is overloaded on the column it may also exhibit peak shape "problems". Peaks can "front", "tail", be truncated or exhibit other non Gaussian shapes due to poor quality chromatography (or lack of training). This should not be confused with the peak width measurement, which is a value we often use to calculate many chromatography parameters from. *Note: Peak width is mostly the result of diffusion over time.
- Maybe your question should have been "Is there any relationship between HPLC peak width and retention time?" *When running in isocratic mode, there is one.
K prime is a measurement of how well retained a sample is on the column. In general, for isocratic methods, peaks tend to become broader and broader the longer they are on the column (diffusion). So a peak that has a large K prime which is run in an isocratic mode may indeed have a wide base (peak width), but a peak which elutes earlier and has a a low K prime may have a narrow peak shape (what we are really talking about here is peak WIDTH). This is often true for isocratic modes because the mobile phase composition is unchanged throughout the run so diffusion plays a more important role. However, with gradient elution, we can change the solvent composition over time and even reduce the peak width of compounds which elute at just about any retention time so clearly we can not say that a peak's K prime value is predictive of its peak width.
Have you read some of the basic books on liquid chromatography? Classics such as "Introduction to Modern Liquid Chromatography" will provide you with the basic fundamentals that we use in chromatography. I think it would answer most of your questions far better than these web forums would. The websites are poor for teaching such a complex technique, but a book can provide you with a detailed explanation of terms and examples of the basics which you can read at your own pace.
Resolution is a function of the capacity factor (R=k/1+k). I don't believe capacity factor should be directly related to peak shape. Assuming you are not expiriencing severe peak distortion or atypical chromatography, the retention time should be reproducible. I believe you do want the capacity factor of your peak of interest to be between 2 and 20 though.
Maybe this article will be helpful to you: http://quimica.udea.edu.co/~carlopez/cromatohplc/forma_peak_2004.pdf
By the way: A good peak shape is always desirable in chromatography (regardless of whether you only work qualitatively or quantitatively). In order to confirm a retention time, a good peak form is essential (I implicitly assume that co-elution is absent).
You appear to be confusing the terms and relationships of some of the fundamental chromatography terms. As its name implies, peak shape is related to the whole shape of the peak seen on the chromatogram. The shape seen may be affected by such things as: the sample's chemistry, injection solvent used, concentration and how it reacts to the column chemistry and/or mobile phase. For example: If it is poorly ionized or not fully dissolved, then it may exhibit a non-Gaussian shape. If the sample is overloaded on the column it may also exhibit peak shape "problems". Peaks can "front", "tail", be truncated or exhibit other non Gaussian shapes due to poor quality chromatography (or lack of training). This should not be confused with the peak width measurement, which is a value we often use to calculate many chromatography parameters from. *Note: Peak width is mostly the result of diffusion over time.
- Maybe your question should have been "Is there any relationship between HPLC peak width and retention time?" *When running in isocratic mode, there is one.
K prime is a measurement of how well retained a sample is on the column. In general, for isocratic methods, peaks tend to become broader and broader the longer they are on the column (diffusion). So a peak that has a large K prime which is run in an isocratic mode may indeed have a wide base (peak width), but a peak which elutes earlier and has a a low K prime may have a narrow peak shape (what we are really talking about here is peak WIDTH). This is often true for isocratic modes because the mobile phase composition is unchanged throughout the run so diffusion plays a more important role. However, with gradient elution, we can change the solvent composition over time and even reduce the peak width of compounds which elute at just about any retention time so clearly we can not say that a peak's K prime value is predictive of its peak width.
Have you read some of the basic books on liquid chromatography? Classics such as "Introduction to Modern Liquid Chromatography" will provide you with the basic fundamentals that we use in chromatography. I think it would answer most of your questions far better than these web forums would. The websites are poor for teaching such a complex technique, but a book can provide you with a detailed explanation of terms and examples of the basics which you can read at your own pace.
- "do I need a good peak shape to confirm the retention time of analytes ? "
You need well developed HPLC methods with highly reproducible runs to confirm peak retention times.
Characteristics of high quality chromatograms include Gaussian peak shapes. Peaks with non-Gaussain shapes can result in integration variations of where the peak apex is. * Flat stable baselines and Gaussian peak shapes make high quality integration possible.
Retention time and peak shape are separate components. You can have a fat peak with a long retention time (or short). You can have a sharp peak with short or long retention time. A chemist should develop the best possible condition to retain the analyte away from the solvent front (k' between 1-10) and away from the interference or coelution peak. At the same time, the peak should be sharp and symetrical to get the accurate retention time and quantification. Both factors can be optimized by adjusting the proper stationary phase and mobile phase. You can be sloppy as much as you want and pay it later for the unreliable method. You can also spend more time optimizing the condition to get a rugged and reliable one.
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