# Creating 100mg/L aspirin solution

I plan on creating 100 mL of 100mg/L aspirin solution by dissolving 10 mg of pure aspirin powder in 100 mL of buffer solution (of different pHs). Problematically, aspirin doesn’t tend towards dissolving in polar solution easily, so I thought about dissolving the 10 mg of aspirin in 1 mL of ethanol first, and then taking that ethanol-aspirin solution and adding it to 99 mL of the buffer solution.

I was wondering if this method seems reasonable/feasible. If not, are there any better suggestions?

• The salts of aspirin are much more water soluble Aug 8 '20 at 6:37

According to Wikipedia, solubility of aspirin in water is $$\pu{3 g/L}$$ or $$\pu{3 mg/mL}$$ at $$\pu{25 ^\circ C}$$. Thus, it is not hard to make a $$0.3\% (w/v)$$ aquious aspirin solution (maximum concentration, which equals to $$\pu{300 mg}/\pu{100 mL}$$ at $$\pu{25 ^\circ C}$$). Therefore, your target, $$\pu{10 mg}/\pu{100 mL}$$ at $$\pu{25 ^\circ C}$$ can be easily achieved without any modifications. You have not mentioned the what different $$\mathrm{pH}$$ values of buffers you are planning to use. Since $$\mathrm{p}K_\mathrm{a}$$ of aspirin is about $$3.5$$ and the amount of it above your target value would dissolve in water (so final $$\mathrm{pH}$$ would be around $$2.12$$ for $$\pu{300 mg}/\pu{100 mL}$$ soution), it is guaranteed to dissolve your desired amount in any buffer with $$\mathrm{pH}$$ above $$2.12$$.