Provided is a method for fabricating a photomask. A method for treating abdominal discomfort associated with irritable bowel syndrome in a mammalian subject includes administering an effective amount of 13,14-dihydro-15-keto-16,16-difluoro-18-methyl-prostaglandin E1 or 13,14-dihydro-15-keto-16,16-difluoro-prostaglandin E1, or a salt, ether, ester or amide thereof, to the subject. Then, measure a first ion beam current received by the Faraday cup and a second ion beam current received by the measurement device. Collected fractions of eluate can also be recycled through the sulfonamide media.