Semaglutide impurity D-Ser8 TFA Salt; L-histidyl-2-methylalanyl-L-α-glutamylglycyl-L-threonyl-L-phenylalanyl-L-threonyl-D-seryl-L-α-aspartyl-L-valyl-L-seryl-L-seryl-L-tyrosyl-L-leucyl-L-α-glutamylglycyl-L-glutaminyl-L-alanyl-L-alanyl-N6-((N-(17-carboxyheptadecanoyl)-L-γ-glutamyl)amino-10-oxo-3,6,12,15-tetraoxa-9-azaheptadecanan-1-oyl)-L-lysyl-L-α-glutamyl-L-phenylalanyl-L-isoleucyl-L-alanyl-L-tryptophyl-L-leucyl-L-valyl-L-arginylglycyl-L-arginylglycine