You will notice that there are many peaks in the chromatogram and your analyte is one of the peak. Did you know the identify of your analyte? You would inject the know standard and it should have the same retention time as the peak of interest in your sample. To calculate the amount is to divide the response of peak in the sample with response of standard and multiply with the concentration of that standard. However, the concentration of the standard must give the response in the same magnitude of your unknown (single point calibration) to make it accurate. Otherwise, you have to inject different concentrations and plot a calibration curve (response vs concentration) and hope that the response of your unknown falls in this region and use the curve to find the concentration in you sample.  This is a basic quantification technique for a chromatographic method that you should be able to find in any fundamental chromatography text book in the library.

I concur with the response above.  You need to make standards with known concentrations of the chemicals you are looking for.  All the peaks represent compounds in your sample or artifact.  With pure standard solutions of known quantity you can identify time of the peak in standard with unknown peaks in sample and match up times.  Measuring quantity is a little trickier but if you have good software it may extrapolate area for your standard of know concentration and approximate your unknown sample concentration by measuring area under the peaks of both known and unknown.  If you do not see a peak in sample that corresponds to the known standard, chemical of interest may not be present in sample or it may be masked by one of the other peaks. Changing characteristics of the buffer can result in changing retention times for better separation on the column.  Note of caution, depending on the neurotransmitter of interest you need to consider many things.  Electrochemical detection is good for some (i.e. monoamine)  not so great for others (Glutamate, GABA, GLY).  In some cases you may not find neurotransmitter but only its metabolites  Serotonin likely very little but huge peak for main metabolite 5-HIAA and least in the work I have done.  Sample handling is critical too.  Monoamines are very labile at room temp and if not sealed air tight or handled in a timely manner your measurements will not be accurate.

Hello Dr. Chamkasem,

                  Thank you so much for your elaborated answer about the neurotransmitter quantification, really it will be very helpful to analyze my data.

Hello Dr. Mark,

            Thank you so much for your suggestion. Yes, first I have run with standards which are purchased from sigma chemicals then sample retention time and peak area were compared. with standards. Now I am clear with the quantification. thanks a lot for your clarification. 

I will send you a paper which ones are you looking to quantify? I would also advise that some are unstable.

Dear Dr. Mark E Obrenovich,

                     Thanks for your help. please send me that article.