New high-grade corporate and agency issues totaled close to $2.5 billion yesterday, excluding Schering-Plough's $828.556 144A eligible private placement. "You can split all the hairs you want to. It's still a really good day," one analyst said. Schering-Plough sold $828.556 million face value of zero coupon notes due 1996. The noncallable notes were priced at 69.839 to yield 7.31% or 78 basis points over comparable Treasuries. Moody's Investors Service rates the deal Aa2, while Standard & Poor's Corp. rates it AA. Merrill acted as placement agent. Student Loan Marketing Association sold $500 million of floating rate notes at par. The notes due 1995 were priced to yield 30 basis points over three-month Treasury bills. Merrill Lynch managed the transaction. ITT Hartford offered a two-part deal totalling $300 million yesterday.