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In a Russian document I'm translating, an HPLC system is used to analyse the amino acid content of a substance.
The detector wavelength is set at 262 nm for "secondary amino acids" and 338 nm for "primary amino acids". But what are those?
I googled and found a lot of mentions with exactly these wavelengths being used, but I haven't been able to quickly understand how a "primary" amino acid differs from a "secondary" one. Is it that the secondary amino acids are the products of the destruction of the primary amino acids (those that initially existed in the substance)?
What is the difference between a "primary amino acid" and a "secondary amino acid"?
I would guess that 'secondary' refers to amino acids that have been derivatized in some way, possibly by reacting with o-phthalaldehyde. (To measure the fluorescence of an OPA-derivatized amino acid, you excite at 340 nm, so I presume the derivative will absorb at this wavelength?).
Based on the reference I read for my biochem exam, secondary amino acids are those which are made of primary amino acids by adding some materials to them for ex :
- hydroxylysine is made by hydroxilation of lysine
- cystine is made by integrating two cysteins so cysteine is primary but cystine is secondary
- etc but in other references the explanation maybe different :)