In T 990/96 (OJ 1998, 489) it had to be examined whether the feature in dispute, which in fact represented a specific degree of chemical purity (in particular diastereomeric purity), constituted a "new element" imparting novelty to the claimed subject‑matter. The board stated that it was common general knowledge that any chemical compound obtained by a chemical reaction would normally contain impurities for various reasons and that it was not possible for thermodynamical reasons to obtain a compound which was ‑ in the strict sense ‑ completely pure, i.e. totally free of any impurity. It was, therefore, common practice for a person skilled in the art of preparative organic chemistry to (further) purify a compound obtained in a particular chemical manufacturing process according to the prevailing needs and requirements. Conventional methods for the purification of low molecular organic reaction products, which could normally be successfully applied in purification steps, were within common general knowledge. It followed that, in general, a document disclosing a low molecular chemical compound and its manufacture made this compound available to the public within the meaning of Art. 54 EPC 1973 in all grades of purity as desired by a person skilled in the art (T 392/06).

In T 728/98 (OJ 2001, 319) the applicant (appellant) argued that the situation was such an exceptional one as mentioned in T 990/96. The claimed pharmaceutical composition differed from the state of the art because the particularly high purity level of the compound it contained could not be achieved by conventional methods. The board found, however, that the applicant, who bore the burden of proving this allegation, had not provided the necessary evidence. Where the claimed purity level of a low molecular chemical compound (here a terfenadine derivative) turns out to be successfully achieved by applying a conventional purification method on a reaction mixture disclosed in the prior art, an exceptional situation such as addressed in decision T 990/96 does not exist. This would have required evidence that conventional methods could not achieve that purity level. Therefore the general rule applies that the level of purity of that low molecular compound cannot entail novelty. That general rule is valid also in the case of a product-by-process claim where that purity level is the inevitable result of the preparation process indicated in the claim.

In T 112/00 the board considered a composition including a solvent having a purity greater than 99% to be new over a prior art composition containing such a solvent whose purity was not specified. The board stated that the claimed composition could be considered as a final product and the solvent as the starting material. As in T 786/00, novelty would be established by the defined purity of the starting material.

The issue in T 803/01 was the novelty of a pharmaceutical composition which differed from prior-art compositions only in the degree of purity of one of its components. In the board's view each and every purification method, provided it was "conventional" but regardless of the extent of purification sought, was presumed to be automatically available to the public, and that in a fully enabling way, so as to amount to an effective novelty-destroying disclosure. As stated in T 100/00 in this respect, the term "conventional" could only mean "conventional in view of the concrete technical context concerned". Therefore the question of whether the degree of purity for the polylactide required in claim 1 provided a new element over the prior art had to be assessed in the concrete technical context concerned.

In T 142/06 the board noted that it followed from the considerations made in decision T 990/96, according to which a document disclosing a low molecular compound and its manufacture normally makes this compound allowable in all desired grades of purity, that the purity level of an organic compound is as such not an essential feature for the definition of this organic compound. However, in the case at issue it was evident that the content of chlorine ion of the claimed latex was an essential feature of the claimed latex, since, according to the patent in suit, only the latexes having this low level of chlorine ions enabled the production of films having the desired properties in terms of oxygen barrier properties and boil blushing properties. This implied that the claimed degree purity in terms of chlorine ion content could not be considered as an arbitrary degree of purity but that it amounted to a purposive selection. Thus, for this reason the considerations made in decision T 990/96 and, by way of implication, in decision T 803/01, did not apply to the case before the board.

In T 1085/13, the board decided that a claim defining a compound as having a certain purity lacks novelty over a prior-art disclosure describing the same compound only if the prior art discloses the claimed purity at least implicitly, for example by way of a method for preparing said compound, the method inevitably resulting in the purity as claimed. Such a claim, however, does not lack novelty if the disclosure of the prior art needs to be supplemented, for example by suitable (further) purification methods allowing the skilled person to arrive at the claimed purity. The question of whether such (further) purification methods for the prior-art compound are within the common general knowledge of those skilled in the art and, if applied, would result in the claimed purity, is not relevant to novelty, but is rather a matter to be considered in the assessment of inventive step. Further, the board was convinced that the rationale of T 990/96 and T 728/98 was not in line with G 2/88 and G 2/10.