Exhibit 10.13 FIRST AMENDMENT TO STOCK PURCHASE AGREEMENTS AND WAIVER This First Amendment and Waiver ("Amendment"), effective as of March 5, 2002 to the Stock Purchase Agreements, dated March 30, 1999 and February 1, 2001, respectively (the "Purchase...Stock Purchase Agreements and Waiver • March 29th, 2002 • Hudson Technologies Inc /Ny • Wholesale-machinery, equipment & supplies • New York
