3 sentences

1. 他的英语口音非常纯正。

   tā de Yīng​yǔ kǒu​yin fēi​cháng chún​zhèng.

   His English accent is very authentic.

   Source: Dong Chinese Dictionary

2. 这种丝绸的色非常纯正，没有杂质。

   zhè zhǒng sī​chóu de sè fēi​cháng chún​zhèng, méi​yǒu zá​zhì.

   The color of this silk is very pure and free of impurities.

   Source: Dong Chinese Dictionary

3. 他从事这项工作的动机非常纯正。

   tā cóng​shì zhè xiàng gōng​zuò de dòng​jī fēi​cháng chún​zhèng.

   His motives for doing this work are very pure.

   Source: Dong Chinese Dictionary