You will want to remove any sodium azide (which interferes with the modification reaction) or gelatin (which has Lys). The azide can be removed by the desalting column or buffer exchange column included in the HRP kit. The gelatin is more of an issue because of its size – will not be removed by the buffer exchange (size exclusion column). Commonly used additives include preservatives such as sodium azide, thimerosal, protein stabilizers such as BSA or gelatin and/or small molecule additives such as glycine or trehalose. Protein carriers such as BSA or gelatin must be removed before labeling can proceed. Remove and purify away all protein carriers such as BSA or gelatin by affinity or other chromatographic methods, re-adjust the initial antibody concentration to 1 mg/mL. or, you can ask the antibody vendor to NOT add any stabilizers to your antibody preparation. The antibody-HRP conjugate should also be stored at 4ºC, and should be stable for at least one year.