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NeuroScience Associates

Mounting Solution/Free-Floating Sections onto Slides


Stock Acetate Buffers:
For reference:1M Acetic Acid
(15mL Glacial Acetic Acid/
235 mL H2O)
1M Ammonium Acetate
(19.27g/250 mL H2O)
Working Acetate Solution:
4.9 pH =
15 mL (1M)
35 mL (1M)
Acetic Acid
Ammonium Acetate
6.0 pH =1.875 mL (1M)
48.125 mL (1M)
Acetic Acid
Ammonium Acetate
Subbing Solution:
20 mLH2O @ 60° C
Stir until dissolved
Working Solution:
188 mLdH2O
12 mLAcetate Buffer (4.9 or 6.0 pH)
50 mL95% ETOH
2 mLSubbing Solution



NSA Labs® will send remaining free-floating sections from sectioned blocks, if the client chooses. Here are some instructions on how to mount the sections onto subbed slides.

List of Supplies:
  • “Hockey sticks” to transfer tissue (Available through our Histotools store)
  • Subbed slides (Available through our Histotools store)
  • Shallow glass dish
  • Small paint brushes
  • Acetate (NOT phosphate!) buffer with a pH of ~5 (recipes below)
  • Kimwipes (or similar lint-free towel)
  • Drying rack (optional)
  • Wet the slide with mounting solution before placing the section onto the slide.
  • Swirl the solution in the dish with the brush to elevate the section from the bottom.
  • Alternately move the corners of the section up the “ramp” of the slide, continuing to scoot the section to it’s “final destination”.  The gelatin matrix is sturdy, thus make efforts during adjustments to contact the gelatin rather than the tissue portion of the Multi-Brain section.  Smooth gentle motions will ensure success.
  • Gradually withdraw and elevate the slide from the mounting solution.  Tip the slide to promote more drainage, while adjusting the section to its proper position.  Make fine adjustments as needed to evenly distribute the section onto the slide.  Pockets of fluid may create the appearance of a pucker, draining will flatten the section.
  • Depending on the stain applied to the sections, the ideal pH of the mounting solution will vary.  Sections that are mounted prior to staining (e.g. Nissl, H&E,) normally do best beginning with a 4.9 pH buffered mounting solution.  Sections that are mounted after staining (e.g. IHC and some specialty stains) normally do best beginning with a 6.0 pH buffered mounting solution. For fine adjustments to the pH see below:
    • If the brain tissue appears too big to “fit” into the gelatin matrix adjust the pH LOWER using 1M acetic acid (e.g. if allowed to dry, the section would show many overlapping wrinkles).
    • If the section appears to be pulling the gelatin inward adjust the pH HIGHER using 1M ammonium acetate (e.g. if allowed to dry, the gelatin would show puckering).
  • Tips for handling free-floating sections may be found here: Link.


Mounting Instructional Video:



For more information:

Antigen Preserve (AP) Solution

Perfusion Fix Solutions

Post-Fixative (Storage) Buffer Solutions