Due to the absence of aromatic side chains, PASylated Tα1 does not absorb light at 280 nm. Thus, for reliable quantification via the peptide backbone absorption, an extinction coefficient at 225 nm was determined. To this end, highly pure Tα1-PAS was lyophilized from water, weighed, and dissolved in a defined volume of water. The concentration of this Tα1-PAS solution was additionally quantified by measuring the backbone peptide groups using UV absorption at 205 nm using a generic calculated extinction coefficient [75], which led to a fair agreement (±6%). The absorbance at 225 nm was measured for various dilutions of the gravimetrically prepared peptide stock solution and plotted against the concentration. The linear range was fitted by a straight line, resulting in an extinction coefficient of 253,057 M−1⋅cm−1. While most buffers strongly absorb light at 205 nm, such a spectral overlap is usually absent at 225 nm.