About cystine determination

[Tequila]

Dear members of this forum,

I need your help in order to get a way to determine cystine and other aminoacids using HPLC with DAD detector with or without derivatization in diferent samples.
Thanks in advance for your help,

Diego

[Mark Tracy]

Amino acids is a whole sub-specialty of HPLC. For UV/VIS detection, the classic is cation exchange chromatography with post-column ninhydrin reagent. You can also use reversed-phase chromatography with precolumn derivatives using OPA/thiol, FMOC, DABSYL, DANSYL, Pico-Tag, or AccQ-Tag chemistries. If you don't want to do derivatization, you can use electrochemical detection (Dionex AAA-Direct). You didn't say what kind of samples, but it does make a difference. If you want total cystine in protein, you probably will want to do a pretreatment with peroxyacetic acid, and measure the resulting cysteic acid. If you want to do it in plasma, you need a reduction step to dissociate it from proteins, then measure the cysteine (reduced form of cystine). Parenteral nutrient solutions don't need any special treatment other than dilution.

Dionex, Waters, Agilent and Pickering all offer supported methods for amino acid analysis.