Why use citric acid in crystal violet staining?

Answer 1

Crystal Violet staining is a technique used in cell culture laboratories to determine concentration of cells in culture liquid.

As against other means of cell staining and counting (e.g. Trypan blue) the entities counted using the Crystal Violet staining are the cell nuclei instead of whole cells. This technique has the advantage that also concentrations of aggregated cells can be determined accurately.

Here comes the Citric acid in. Nuclei are situated within the cell. To extract the nuclei out of the cells Citric acid is used to make the cell burst so that the Crystal Violet can stain the nuleus and thus concentration of cells can be determined using a microscope and a counting chamber.

Answer 2

Citric acid is used in crystal violet staining as a mordant to enhance the binding of the crystal violet dye to the bacterial cell walls. It helps to intensify the staining by promoting better dye penetration and retention, resulting in clearer and more defined staining of the bacteria under the microscope.