The phrase "ascertain it" is correct and usable in written English.
You can use it when you want to express the action of finding out or determining something.
Example: "Before making a decision, I need to ascertain it through further research."
Alternatives: "determine it" or "verify it."
I shall ascertain it later and have the Tribunal informed.
The sawdust of this tree is chosen to ascertain it viability as a precursor for activation.
I do not recall the name of the person who told me, I shall have to ascertain it.
As far as we can ascertain it is the first time a kick-off has been delayed by a single inflatable.
The analysis developed what he had no doubt was blood, but so far as he could ascertain, it was animal, and not human blood.
While cross-country differences in technology costs are hard to ascertain, it is possible to account for the cost of capital on a country-by-country basis.
So that the surveyor general not only had the authority to determine the extent of the grant, as well as its validity, but he had the means of ascertaining it.
By means of a study of the typography and the chemical composition of the paper, they ascertained it to be a fraud.
The comprehensive study conducted in IIT Bombay Shock Tunnel (IITB-ST) has confirmed the performance, ruggedness and reliability of the coaxial thermocouple, ascertaining it to be an effective, impulse, heat flux sensor.
While the exact growth mechanism of CNTs/CNFs formed from fly ash as a catalyst has not been fully ascertained, it appeared that tip growth could not be discounted (as seen by the red-coloured circles in Figure 1e,f).
The robust moral realist, accordingly, would think that a sentence like "Stealing is morally wrong" is either true or false, but that its truth value potentially outruns any means we know of for ascertaining it.
