Hi, never use only 70 % ethanol for DNA storage. It degrades very fast. 

It should be around 95 % or higher. This gives sufficient preservation

conditions, even more when put @ -20.

However, it can still degrade. The best is indeed to purify the DNA and store it @ -80 (in TE buffer or ddH2O) or use the Whatman FTA papers used in

forensics. They might give you good yields afterwards, but you should test this first.

I would suggest flash freezing the freshly collected samples in liquid nitrogen, then storing them at -80. You would then be able to use part of your sample for DNA extraction, and keep the rest for future studies or repeats.

Thank you Bastian and Isabelle for this great advice I appreciate the help. I will get some 100% ethanol  and liquid nitrogen and investigate which storage facilities are available.

have a great day

Leigh

We regularly collect and store tissue samples for DNA extraction from wild animals killed in control programs. We use 95% or higher (usually 100%) ethanol - seems to be the gold standard for reliable preservation. The main issue is to use good storage jars so the ethanol does not leak/evaporate, and use a high volume of ethanol per unit of tissue to adequately preserve the sample. You may also consider freezing (at ~ -18 deg, like a normal household freezer) the jars containing the ethanol/tissue sample, to avoid any spillage/loss of liquid. The main logistical issue is safe transport of ethanol - postage services and some couriers will not transport high % ethanol.

As suggested earlier, Whatman paper may be good too. FTA cards are designed to securely store DNA for long periods without the need for refridgeration - a blood sample is good on these. Might be worth considering for any field data capture where data storage/transport of ethanol may be an issue.

I agree with some of the advices above: just freeze your samples and you are sure DNA is preserved for a very long time in a minimum space without the trouble of spilling evaporating alcohol etc.. The only disadvantage is transporting it after freezing, but I guess is equally problematic with alcohol.

I would definetely freeze after collection. If you can get liquid nitrogen and than transport in thermal jars that would be fine.

If you are storing skin samples, and they are very fresh, you will get the best yield of high molecular weight DNA if you manage to freeze them immediately in liquid nitrogen. This is often not practical in the field so in that case, 70% ethanol will be fine. Tubes can be kept at room temperature, at +5 C or in a -20 C freezer, whatever is most convenient.

For extracted DNA following a phenol-chloroform extraction - my understanding is that the best way of storing the DNA is at the final step where you pellet the DNA in the centrifuge after washing with ethanol. You can freeze the tube, with the pellet (and ethanol) and this should be very stable.

Thank you everyone who has contributed (sorry I did not reply earlier) I have 100% ethanol in field kit and arranged some space in a -80 freezer till nitrogen storage can be negotiated.

Happy New Year