Ran An To determine the calcium concentration in the hydrogel, you need to weigh a sample of the hydrogel. Dry the sample to a constant weight. The water content and swelling properties of the gel can now be determined. Then you need to burn the sample and determine the ash content. Submit the ash for chemical analysis. Then recalculate the calcium content in the ash to the calcium content in the gel.
Ran An To obtain the distribution along the layer depth gradient, you need to make a slice. Then take samples from different depths. It can be done differently, but then you need to dig from old articles.