Daniel Noboa said his team had proof to support the claim, though he has yet to publicly provide any evidence.
The South American leader told CNN on Thursday that he believed it was "practically impossible" that the three chemicals would be found in high concentrations in the items by chance.
His comments come in the wake of violent clashes in Ecuador over a sharp rise in fuel prices under his presidency. The centre-right politician has brought in military crackdowns on drug gangs, but has also faced accusations of targeting protesters.
Noboa has denied the allegations of attempts on his life - the third in two months - were a means of portraying his detractors as violent.
"No one throws a Molotov cocktail at themselves... or poisons themselves with chocolate, or throws stones at themselves," he said, referring to previous incidents.
Early in October, Ecuador's government said five people were detained over what it described as an alleged assassination attempt.
About 500 people threw rocks at the president's car and there were "signs of bullet damage" on his vehicle, according to the country's energy and environment minister, who added that Noboa was unharmed.
The BBC was not able to independently confirm that a bullet had been fired.
