Dr Ahmad and two other volunteers travelled to the attack sites to collect evidence in a mission that ran the gauntlet of kidnapping, arrest, shelling and air strikes.
"I did this for the simple reason that I wanted to show the world that chemical agents had been used," he said after arriving in Turkey, with samples labelled and bagged. "I did it methodically. I filmed everything. I wanted to be sure that I have the whole chain of custody without interruption [from collecting the samples to seeing them tested] so when the results come, we know that they are accurate."
Dr Ahmad, a medic in rebel-held Aleppo, first took an interest in chemical weapons during an attack on the city in March last year.
"There was chaos in the hospitals. Doctors became contaminated treating the wounded. People were so afraid and didn't know what to do. I studied the process of decontamination and medical treatments on the internet."
Later in the year, he was part of a group of Syrian medics trained by Western chemical weapons experts in how to react in a chemical attack and the procedure for collecting samples in the aftermath.
Last month, news reached him from colleagues near Kafr Zita that casualties of recent bombings were displaying unusual symptoms: eye and skin irritation, respiratory distress, a bloody froth from the mouth.
With two fellow volunteers, Dr Ahmad crossed front lines to reach the sites of the attacks. He took GPS readings at the sites and video footage shot at Kafr Zita shows him measuring the remains of the barrel bombs that delivered the chemicals and had been collected by local residents. One was inscribed "Cl2", the chemical symbol for chlorine gas.
They also travelled to a hospital in Saraqeb to collect blood and urine samples from survivors.
"All injuries were the same," said Dr Ahmad. "There were no external wounds, just respiratory distress, irritation of the eyes and skin."