Frank Quattrone, one of the star bankers of the hi-tech boom, was yesterday sent on administrative leave by his employer, Credit Suisse First Boston, because of an investigation into the flotations he conducted for dotcom firms.

The head of CSFB's global technology group, Mr Quattrone ran a team of highly paid bankers in California whose advice was much sought-after during the late 1990s.

Yesterday the 47-year-old banker was forced on to the defensive, saying: "I did nothing wrong. I am confident that the investigation will show that."

Mr Quattrone is facing potential civil charges from the US securities regulator, the national association of securities dealers, for the way he allocated shares during the flotations. He is said to have placed shares that often rose quickly after their debut into "Friends of Frank" accounts.

CSFB said it had sent Mr Quattrone on leave after learning of new information last week which appeared to relate to the timing of a message about whether emails and other files should be kept or destroyed. CSFB said information it had discovered on Friday "raised questions about Mr Quattrone's response to an inquiry last week by the firm about whether he was aware of pending investigations in 2000 when he sent an email to employees regarding document retention issues".

"The new information raised questions about whether Mr Quattrone acted appropriately in December 2000 when he sent that email and permitted a subordinate to send a similar email to employees."

CSFB, which recently paid $100m to settle regulators' charges relating to the boom, said it had "acted properly" to ensure all relevant documents were preserved. It notified regulatory bodies about the new information last week.