Intention of giving Zakaat
Zakaat is a form of worship and it is universally accepted that acts which are themselves worship (and not a means to worship, like Wudhu, etc.) aren’t valid until the intention is made. The intention for Zakaat can be made when giving Zakaat or when calculating and separating the amount of Zakaat from one’s wealth. If one gives away the amount of Zakaat and then makes the intention of Zakaat, then if the person to whom Zakaat was given is a needy person and not from the family of the Holy Prophet (Sallallahu alaihi wa sallam), then the Zakaat is valid. If someone makes someone else a representative for Zakaat, then it is enough if the intention for Zakaat is made when giving the amount to the representative. As given in Radd Ul Muhtaar, Kitab Uz Zakaat.