Reasons for the formation of inverted peaks in liquid chromatograms
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When working with liquid chromatography, everyone must have encountered all sorts of strange peaks! I’ve been encountering reverse peaks quite often lately. What are the reasons that lead to the formation of an inverted peak? Welcome everyone to come and exchange ideas!~~~
The reasons for the inverted peak are as follows based on some information found: 1. It is often a solvent peak; when the ultraviolet absorption of the mobile phase is greater than that of the solvent in the sample, an inverted peak appears. 2. Impurities in the sample may have no ultraviolet absorption or only very weak absorption, while the mobile phase has strong ultraviolet absorption. This phenomenon often occurs when methanol is used and the wavelength is set below 220 nm. 3. The entry of air during sampling can also cause this issue. 4. If the mobile phase contains impurities with ultraviolet absorption, an inverted peak will be generated when using a UV detector; therefore, a high-purity solvent must be used as the mobile phase. 5. An inverted peak will also occur if the polarity of the detector is reversed.
Everyone can also share here some of the trough phenomena they have experienced as well as the solutions adopted; looking forward to more exchanges!~~~