Complex sentence: To regenerate the column, d-desthiobiotin is removed by application of a HABA solution (a yellow azo dye) and indicated via color change from yellow-orange to red (step 4 +5).
Split into simpler sentences: To regenerate the column, d-desthiobiotin is removed by application of a HABA containig solution (a yellow azo dye). The removal of d-desthiobiotin is indicated by a color change from yellow-orange to red (step 4 +5).