Quantification of vaccine compositions

A method of quantifying the presence of one or more porcine circovirus type 2 (PCV2) viral proteins forming a virus like particle in a sample, the method comprising:

• a) adding a known quantity of one or more stable-isotope-labeled signature peptides specific to the one or more PCV2 viral proteins in the sample, wherein the one or more stable-isotope-labeled signature peptides are selected from the group consisting of:
• i)
• (SEQ ID NO:
• 14)
• ANALTYDPYVNYSSR;
• ii)
• (SEQ ID NO:
• 15)
• HTITQPFSYHSR;
• ii)
• (SEQ ID NO:
• 18)
• LQTTGNVDHVGLGTAFENSIYDQDYNIR;
• iv)
• (SEQ ID NO:
• 19)
• ITMYVQFR;
• v)
• (SEQ ID NO:
• 22)
• YFTPK PVLDR;
• and
• xviii)
• (SEQ ID NO:
• 23)
• EFNLK DPPLNPK;
• b) digesting the sample with a protease;
• c) running mass-spectroscopic analyses of the sample;
• and
• d) determining an amount of the one or more PCV2 viral proteins in the sample, wherein the one or more PCV2 viral proteins are capable of forming a virus like particle and/or wherein the sample comprises virus like particles composed of a plurality of the one or more PCV2 viral proteins comprising PCV subtype 2a (PCV2a) open reading frame 2(ORF2) and/or PCV subtype 2b (PCV2b) ORF2;
• wherein the sample is removed from one of:
• an animal material selected from a body fluid and a tissue, a preparation of the animal material, and a vaccine preparation.