Very odd story. Sodium sulphate is an easy to produce, common commercial product used to manufacture a wide range to items. Nothing "chemical weapons" or "missile" related about this material. And why ship via Turkey? There are much easier routes to Syria from Iran, including air and sea. I am dubious about the entire claim. Am I missing something??
This was first published by today's zaman which is an Anti Iranian Turkish newspaper. But the entire claim is foolish I think. If Iran wanted to send something of high importance to Syria, air routes were the best ones. Not via trucks from Turkey.