How can I get the SD of baseline noise?

Hi all,

This current signal was filtered at 3 kHz, and digitized gap-free signal was filtered at 6.25 kHz (160 microseconds). The y-axis is current in pA, and the x-axis is time in seconds.

I need to get the SD of the baseline noise, so the first approach I made was to calculate the SD of the signal during the beginning (0.2 - 0.6 s) of the recording because there is no spike and the baseline does not drift. I did it because the noise is the 'width' of the signal during the 'rest' period (baseline), right? So, a higher width has a higher SD. Therefore the signal is noisier, right?

I was trying to get this parameter around by the signal-to-noise ratio. But I neither have the power of the signal nor the power of the noise. I can get the power of the signal, but I understand nothing here. Honestly, I am very confused, do I need all this parameters in order to get the SD of the baseline noise?

So my question here: Is the SD of the baseline of the signal equal to the SD of the baseline noise?

Many thanks!

Jose