You should use more trizol and waiting in trizol may be better for concentration. On the other hand, for PMBC the purity rate should close to 2.0.

needle is not necessary, using enough amount trizol is better

good luck

Thanks Huseyin Ozkan,

I usually use 1 ml Trizol but sometimes 700-800 ul because I thought with less Trizol, phenol contamination will be less too.

what should I do for purity?

Do not be greedy when you take the supernatant, avoid as much as possible taking from the interface or the organic phase.

You can run the obtained RNA on a silica column. This will remove any organic compound contamination and increase purity.

Alternatively you can use a silica-column based kit from the start of the extraction.

Also you can try to wash rna with 70 % Et-OH, more than two times

Thanks Huseyin and Abdullah for the reply.