Hi all,

We filtered seawater and preserved the filters in RNAlater on site. The tubes with the sample in the RNAlater were placed in a cold box until arrival in the lab where they were left overnight at 4C. After this they were placed in a freezer at -20C still in the RNAlater until they were processed a couple of weeks later. When we retrieved the samples for processing we realised that some of the samples where frozen while others weren't, there doesn't seem to be a reason for this difference (other than maybe some samples where a bit more wet than others?).

My questions are:

1. Is this a problem in the long term? There seems to be a bit less RNA in the frozen samples (measured with the nanodrop) but very minor and we did process the samples soon after arrival in the lab, will this be a problem if we store the samples for long periods of time?

2. Is there a way to avoid this? Was this caused by extra moisture in the sample?

Maybe I am looking this the wrong way around and samples are supposed to freeze and they didn't because the salt content or another reason and we should aim at freezing them.

Any thoughts will be greatly appreciated.