One thing that stood out was this image, of one of devices supposedly used to deliver the chemical
What stands out about this is it appears to be a very strong match to the remnants of devices that were supposedly used in an earlier attack in Sheikh Maghsoud, Aleppo, for example
Note the large ridge, and these two features
Also note the top of the item in the Saraqeb images, and this image
There's also been a video posted online showing what is supposedly the attack occurring, and this does not appear to match to any form of attack I've seen in Syria before, and looks very much like something falling through the sky producing smoke/gas (h/t James Miller of EA Worldview)
This leads me to believe the same devices and chemical were used in both attacks, but as yet it's unclear what the chemical and device is.
Update April 29th 2013 Something else that links the two attacks is the description of the earlier attack, via Mohammed Aly Sergie
Some survivors said the canisters were dropped from a helicopter, but others didn't hear rotors. Doctors don't know what the chemicals wereUpdate April 29th 2013 Another video has been uploaded showing the victims, and a much clearer shot of the device used
This extra detail on this video seems to prove that the devices used in both attacks were identical.
Update April 30th 2013 Thanks to Anita McNaught of Al Jazeera English for sending me this new video show the canister much more clearly
A Great Example Of How Not To Write About Chemical Weapons And Arms In Syria