Generally, bromophenol blue is added to the loading buffer, and the dosage is not strictly limited, as long as there is color, which only plays the role of marking the front. The position of bromophenol blue is approximately equivalent to the mobility of a DNA fragment of about 500bp (in 0.8 agarose gel).

General commercial DNA markers (such as Trans 2K) come with commercial 6X loading buffer, which contains bromophenol blue, glycerol and so on. , can be used directly.