Waters offers two methods for AA analysis: Pico-Tag and AccQ-Tag. Both are described in European Pharmocopoeia as common aproach for AA analysis (chapter 2.2.56 method 3 and 4 respectively). Based on this they should be treated as compendial methods, taking into account all requirements given in the monograph. However it should be known that EP monograph 2.2.56 gives only general principles and general rules of the method so you should conclude that the monograph probably covers Pico method and AccQ method as it is described by Waters in their official documents.
In my opinion AccQ method is better and easier to perform.
This is not an AOAC Official Method of analysis. I am not aware that it is in the United States Pharmacopeia. Stand alone separation and detection techniques may appear in official compendia, but this does not make them official or even compendial methods. In order to achieve official status, accuracy, precision, and reproducibility data would be needed for the entire method (including sample preparation). In addition, official methods must state the method's scope, including the matrix on which the method has been evaluated.
European Pharmacopoeia gives general principles ,but i ask this question because i have problems during analysis of free amino acids,
1-the peak area of the sample and standard increased if they re-injected after a period of time(example, 3 hrs) during sample set .
2-what precautions to decrease noises during sample analysis?
(i use Pico-tag method)
I don't know Pico method in details, but I would ask u two questions:
1. Do u apply cooling in your autosampler? As sample solvent contains 40% ACN it can be an effect of temperature and thus volume compression which is higher for organic than for water solutions. On the other hand you should consider evaporation of the solvent.
2. Do you use internal standard? If yes, your related peak areas/heights should remain unchanged, because any effect usually applies to all AA-derivatives in the sample.
I have no other ideas... Good luck.
thanks Małgorzata Jaworska, it is appropriate reason if i take evaporation of solvent ( which contain acetonitrile )in consideration because my sample set usually take 24 hrs.
and also,i use α-amino butyric acid as internal standard and yes there is no change in response(area of each item/area of internal standard) and it gives the same percentage(%).
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