Are you sure your precipitate is not MSU microcrystals? In human tissues MSU appears as a milky slurry of crystals about 10microns long. If you look at your precipitate under a polarising microscope you should see negatively birefringent needles. If you want larger crystals of visible size you would probably need to cool much more slowly (over days) or start with a more dilute solution and allow evaporation. (I have never seen an MSU crystal big enough to see by eye.)

Dear Prof. Edwards,

Thank you very much for your response.

I followed your suggestion to look under polarising microscope and yes i found something look like crystal.

Is it possible if there's another shape of crystals? because i found there're various kind of shape of crystals, not only needle-shape crystals. Or is it because of impurities? i mean, maybe i do something wrong while preparation process...

I think the crystal shape may depend on the speed of crystallisation, but there may also be other salts precipitating. I am afraid I do not know the technical details here. I am not sure what you want to use these crystals for. The mechanism by which MSU crystals cause inflammation is very complex and may be dependent on crystal size, presence of adsorbed proteins and a whole range of other things. Even with the needle shaped crystals found in deposits in man the great majority of such deposits (tophi) are associated with no inflammation. You may find useful information in the literature from the 1980s by people like P Dieppe and M Docherty.

Maybe you can get the mososodium urate salt from the sigma. I research the gout and tried to get the msu crystals for many times, and what i have gotten is the crystals just like what you have gotten. so, next time ,i will try use the  salt gotten from sigma to do the research.

MSU crystals were prepared by first dissolving uric

acid (5 mg/ml) in 0.1 M borate buffer (pH 8.5), and, after passing through

a 0.45-mm filter, the supersaturated uric acid solution was left at room tem-

perature for 48 hours. The large crystals formed during the first 48 hours

were removed by centrifugation, and the supernatant uric acid solution

was incubated at room temperature for 5 more days to allow the formation

of fine crystals, which were harvested by centrifugation. After 2 washes

with absolute alcohol and 1 wash with acetone, the crystals were allowed

to air dry. Crystal size varied between 3 mm and 50 mm in length, with

48% of crystals less than 10 mm in length and a mean ± SD crystal size of

11.69 ± 6.6 mm. All reagents were prepared under pyrogen-free conditions.