A number of purity options are offered at 21st Century Biochemicals. These include ordering the peptide in its crude state that is suitable for use in preliminary experiments only. Since the purity of a crude peptide typically decreases as the length increases, short peptides can be provided as crude peptides for some applications. Once the length of the peptide increases to beyond 12-15 amino acids, the purity of the crude product and thus the eventual yield of final, desired, product will decrease. For the production of antibodies, we have found that peptides purified to at least 85% purity will improve the immunological response and the production of specific, high titer antibodies. We discourage the use of crude peptides to elicit an immune response. For ligand binding studies, competition studies, or any other highly sensitive bioassay, it is critical that the source of the signal generated can be attributed to the peptide of interest. Thus we tend to recommend that peptides be purified for such use to at least 90% and often 95+% purity to insure reliability and most importantly reproducibility of the experiments. A consultation with our scientists or sales staff can often provide guidelines as to the proper purity to use for your intended research application.