Determiantion loss on drying; minoxidil

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winzzz's picture
Determiantion loss on drying; minoxidil


 --- minoxidil ----
BP specfication ; loss on drying
 ----> not more tan 0.1% ,determined on 1.000 g by  in oven 100-105 C
In minoxidil monograhp and appendix IX D.Determination no describe to duration drying in oven.
In this case ,How long to dry it in oven?

thank you very much.

Dr. Analytical
Dr. Analytical's picture
As a general rule, you should

As a general rule, you should dry your sample to "constant mass."  That means that you continue drying until the mass is constant, so multiple measurements are required.

For this compound, you could measure loss at two hours and four hours, and if the loss is less than 0.1% you could state that the compound meets the specification.

Note: you will need a balance with 0.0001 g sensitivity.

ToxLabRat's picture
Dr Analytical is right

Dr Analytical is right however if you are looking for a ballpark time of how long it is going to take, I was able to find this which says that when doing the loss on drying method for minoxidil you need to dry for about 3 hours. Sorry but I couldnt get the ad banners to cut out of this post, so just ignore them and look below... 

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C9H15N5O 209.25

2,4-Diamino-6-piperidinopyrimidine 3-oxide [38304-91-5].

»Minoxidil contains not less than 97.0percent and not more than 103.0percent of C9H15N5O,calculated on the dried basis.

Packaging and storage— Preserve in well-closed containers.
USP Reference standards á11ñUSP Minoxidil RS.
Identification,Infrared Absorption á197Mñ— Do not dry specimens.
Loss on drying á731ñ— Dry it at 50and at a pressure not exceeding 5mm of mercury for 3hours:it loses not more than 0.5%of its weight.
Residue on ignition á281ñ: not more than 0.5%.
Heavy metals,Method IIá231ñ: 0.002%.