Bismillah,
Asalamu Alaykom,
After doing istibra you can assume any drops are pure and your wudu remains valid.
May Allah grant you success
Seyed Ali Shobayri is of mixed Iranian and Scottish descent who found the path of the Ahlul Bayt (a) by his own research. He holds a BA in Islamic Studies from Middlesex University through the Islamic College of London. He also studied at the Hawza Ilmiyya of England and continues Hawza and Islamic studies with private teachers.