Hi. You can try the following method (a sensitive and specific HPLC-UV method for the quantification of methionine in serum after derivatization with PITC).
There is lot of methods available for analysis of methionine as many of my friends recommend you. May be most of these methods you already know. I am also giving you a method. If you have any other analytical issue .you must share.
Methionine can be analyzed by Amino acid analyzer or HPLC with Fluorescence detector . Proper sample preparation is required before injecting sample in it. Use ACN for final dilution.