substituted by --COOM or methyl, and ##STR16## R7 and R8 are respectively a radical selected from the group of hydrogen, hydroxyl, and --C2 H4 OH; R9 and R10 are respectively a radical selected from the group of hydrogen, amino, hydroxyl and lower alkoxy; n is 1 or 2; m is 0 or 1; and M is an alkali metal or ammonium.