Antibody composition and buffer system therefor

1. A method for conjugating an isolated antibody to a label or derivatisation reagent, which method comprises contacting the antibody with an activated label or activated derivatisation reagent, or contacting the antibody with the label or derivatisation reagent in the presence of an antibody conjugation reagent, in a buffer system which comprises a monocarboxylic acid buffer compound having an amine substituent at the alpha or beta position, wherein the monocarboxylic acid buffer compound is not glycine and wherein the antibody conjugation reagent, activated derivatisation reagent or activated label comprises one or more reactive groups for conjugation to the isolated antibody, the one or more reactive groups being selected from: a carbodiimide, an N-hydroxy succinimide ester, a maleimide, an isothiocyanate and a thiolation reagent.

2. A method according to claim 1 , wherein the monocarboxylic acid buffer compound further comprises one or more non-amine substituents or no further substituents.

3. A method according to claim 1 , wherein the amine substituent of the monocarboxylic acid is a secondary or tertiary amine, or quaternary ammonium.

4. A method according to claim 3 , wherein the amine substituent is a quarternary ammonium substituent.

5. A method according to claim 4 , wherein the monocarboxylic acid buffer compound is a betaine.

6. A method according to claim 5 , wherein the betaine is N,N,N-trimethyl glycine.

7. A method according to claim 1 , wherein the monocarboxylic acid buffer compound is a primary amino acid.

8. A method according to claim 7 , wherein the primary amino acid is alanine, beta-alanine or 2-amino-butyric acid.

9. A method according to claim 8 , wherein the monocarboxylic acid buffer compound is proline, tricine, N-methyl glycine, N,N-dimethylglycine or 2-picolinic acid.

10. A method according to claim 1 , wherein the carboxyl group of the monocarboxylic acid buffer compound has a pKa in the range of from 1 to 4.

11. A method according to claim 10 , wherein the carboxyl group of the monocarboxylic acid buffer compound has a pKa in the range of from 1.5 to 3.5.

12. A method according to claim 1 , wherein the amine of the monocarboxylic acid buffer compound has a pKa of greater than 8.

13. A method according to claim 11 , wherein the amine of the monocarboxylic acid buffer compound has a pKa of greater than 9.

14. A method according to claim 1 , wherein the monocarboxylic acid buffer compound is present at a concentration of less than 200 mM.

15. A method according to claim 14 , wherein the concentration of the monocarboxylic acid buffer compound is less than 100 mM.

16. A method according to claim 15 , wherein the concentration of the monocarboxylic acid buffer compound is less than 50 mM.

17. A method according to claim 1 , wherein the buffer system further comprises a neutralisation buffer compound having a pKa of greater than 5.5.

18. A method according to claim 17 , wherein the neutralisation buffer compound comprises a morpholino, piperazine or N-cyclohexyl compound.

19. A method according to claim 18 , wherein the neutralisation buffer compound is 2-(N-morpholino)ethanesulfonic acid (MES), 3-(N-morpholino)propanesulfonic acid (MOPS), 3-Morpholino-2-hydroxypropanesulfonic acid (MOPSO), (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) (HEPES), 3-[4-(2-Hydroxyethyl)-1-piperazinyl]propanesulfonic acid (EPPS or HEPPS), piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES), N-(2-Hydroxyethyl)piperazine-N′-(2-hydroxypropanesulfonic acid) (HEPPSO); N-(2-Hydroxyethyl)piperazine-N′-(4-butanesulfonic acid) (HEPBS), N-Cyclohexyl-2-aminoethanesulfonic acid (CHES), N-cyclohexyl-3-aminopropanesulfonic acid (CAPS), 4-(cyclohexylamino)-1-butanesulfonic acid (CABS) or 3-(cyclohexylamino)-2-hydroxyl-1-propanesulfonic acid (CAPSO).

20. A method according to claim 17 , wherein the buffer system further comprises a catch buffer compound with a pKa in the range of from 6-8, wherein the neutralisation buffer compound has a pKa above 8.

21. A method according to claim 20 , wherein the pKa of the neutralisation buffer compound is in the range of from 8 to 11.

22. A method according to claim 20 , wherein the catch buffer is MOPS or HEPES.

23. A method according to claim 20 , wherein the concentration of the catch buffer compound is less than the concentration of the neutralisation buffer compound.

24. A method according to claim 1 , wherein the label comprises an enzyme, a fluorescent protein, an organic dye, a coloured particle, biotin, streptavidin or a polymer.

25. A method according to claim 1 , which is carried out at a pH in the range of from 5 to 9.