U.S. Patent No. 8,273,707 is directed to purifying proteins using HIC (pages 2-3). In prosecution, the applicants argued that combination and a particular combination of salts is not taught in the prior art (pages 4-5). A declaration discussing the particular combination as being beneficial was submitted during prosecution (page 5). Due to argument-based prosecution history estoppel, combinations other than the particular combinations recited in the claims were thus surrendered (pages 8-9). “Particular” combinations was argued multiple times, including in the declaration (page 10). A competitor would reasonably believe non-recited combinations where surrendered (page 10). While multiple arguments, including just combination in general, were used, estoppel can attach to each argument (page 11). Not using an argument in the last response does not change that the argument was used (page 12).

Hindsight: It may have been better, but possibly more costly, to argue only the broader claim concept – any combination not being taught. The particular combinations could have been held in reserve. Similarly, the claim could have been drafted without reciting the particular combinations as reliance on doctrine of equivalents in light of specific recitation in a claim may be difficult.