The phrase "a substantial amount but" is correct and usable in written English.
It can be used when introducing a contrast or exception after stating a significant quantity or degree of something.
Example: "There was a substantial amount but it still wasn't enough to meet the requirements."
Alternatives: "a considerable quantity yet" or "a significant sum however".
That would value Facebook at between $50bn and $85bn – a substantial amount, but far from the $104bn£65.8bnbn) that the $38 share price put on it.
"Every year we've managed to exceed our expectations by a substantial amount, but this year we missed the projection," said Julia Erickson, the executive director.
That's a substantial amount, but not enough that it yells gender pay gap.
Often angels or other investors have invested a substantial amount, but not enough to merit a board seat.
I happened to be making a relatively high salary as a computer programmer before hearing about EA, and that allowed me to donate a substantial amount, but I didn't do a very comprehensive analysis of my career options.
Swig, who owned the St. Francis and Fairmont Hotel, claimed that he had topped Hilton's bid by a "substantial" amount, but he wouldn't say by how much because he did not want to be party to a bidding war.
The grant carries with it a substantial amount of money — but it is not without precedent, even in the field of cardiovascular research.
"There is no mistake that there was a flow of a substantial amount of funds, but we have not identified an amount".
These events supply in many dryland ecosystems a substantial amount of water, but their role for northern humid ecosystems is largely unknown.
The deal, which is expected to be completed by the end of the year, will finally allow Viacom to shed the slow-growing Blockbuster business, which generates a substantial amount of cash but is increasingly threatened by services like Netflix and new technologies like video-on-demand, which deliver movies directly to the home.
He suffers a considerable stain on his reputation, has to pay a substantial amount of money but retains significant wealth and at the age of 71 may find the possibility of being an officer or director of another public company less enticing".
