I have a metabolic extract from a plant, when I injected it into the LCMS all the chromatogram peaks are small, although I have increased the concentration several times but there is no change in the surface area of the peaks, is there an explanation for this please?
As the answer before it could be a problem with you Autosampler,
but some other reason could also be:
May be you have a problem with ionsupression if you have enriched matrix compounds. What kind of ionisation do you use? If it is ES,I ionsupression is often presend.
Wrong polarity could also be, do you have tried out positiv and negative mode?
What are your target stuctures? Nonpolar target will not ionisated by ESI, then APCI ist the recommaned ionisation form.
But first look at your sampler. inject a well known sample and look at the peak intensity, it must be in the expacted range. If not, the sampler has a problem.
Not enough information to know why. LC-MS method development is a complex process requiring a great deal of training and knowledge. In general, with LC-MS analysis you need to develop and optimize an HPLC method which allows for both on-column retention and good ionization of each of the specific sample(s). It is all about ionization. Poor ionization equals little to no detection by the MS and changing concentration may not help.
Have you optimized the ionization modes (pos.neg), settings (voltages, gas, temp....) and detection type for each sample type? Is your HPLC method optimized to provide baselines resolution of all peaks? Are you using a second complementary detector inline with your MS so you can "see" the samples, their peak shapes and retention characteristics during analysis? The MS detector alone is not going to show you what is actually there, only the compounds that happen to ionize well under the conditions YOU have selected. You may have to use multiple settings to see all of the compounds present.
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