HPG Protein Modifier, or p-Hydroxyphenylglyoxal, reacts with arginine residues to give a large increase in absorbance at approximately 340 nm, and hence, is a good choice for amino acid side chain modification.

Providing storage is as stated on the product vial and the vial is kept tightly sealed, the product can be stored for up to 24 months.
Wherever possible, you should prepare and use solutions on the same day. However, if you need to make up stock solutions in advance, we recommend that you store the solution as aliquots in tightly sealed vials at -20°C. Generally, these will be useable for up to one month. Before use, and prior to opening the vial we recommend that you allow your product to equilibrate to room temperature for at least 1 hour.