Although the theoritical solubility limit of DCPIP is 10 mg/ml (i.e. 1%), this substance is really hard to dissolve in general. Try using an approximately 0.05% NaHCO₃ solution to dissolve the DCPIP (with constant stirring if possible), leave overnight, and then filter with a standard laboratory filter paper.

Dear Sumona Akter thank you for sharing this very interesting technical question with the RG community. DCPIP (= 2,6-dichloro-phenolindophenol) is a neutral organic compound which in this form is insoluble in water. Thus it makes no difference if your stir the suspension in distilled water for 10 minutes or 3 days. 😥 Only the sodium salt of DCPIP is soluble in both water and ethanol. You can prepare a solution of the sodium salt in water by adding DCPIP in portions to a warm aqueous solution of sodium carbonate (Na2CO3).

Good luck with your experiments and best wishes, Frank Edelmann

Preparation of DCPIP solution:

Dissolve approximately 0.04 g of sodium hydrogen carbonate in 200 mL of distilled water, add approximately 0.05 g DCPIP and dissolve with shaking. This is very hard to dissolve. Leave overnight and filter. Note: DCPIP is NOT a primary standard so the concentration is only approximate. It needs to be standardised.

Calculate the approximate concentration of DCPIP.

Sample calculation: mass DCPIP = 0.050 g

Approximate C (DCPIP) = 0.050/268.1/0.200 = 0.000932 M.

Standardising DCPIP: Pipette 1.00 mL standard ascorbic acid solution in to a conical flask and add approximately 50 mL of extraction solution. This solution contains 0.001 g ascorbic acid. Place the blue DCPIP solution in the burette. Slowly add the DCPIP to the flask and you will notice that the solution goes a temporary pink. Swirl but do not shake and continue adding drop by drop until solution just remains colourless (not pink) and one more drop should send it a very faint grey-blue.

Calculate the exact concentration of DCPIP

Sample calculation: Titre of DCPIP = 7.25 mL

CV (ascorbic) = CV (DCPIP)

0.00567 x 1.00 = C x 7.25

C (DCPIP) = 0.000782 M

Good luck

Dr. Riyadh Ikreedeegh

Riyadh Ikreedeegh Frank T. Edelmann Zoltán Péter Jákói At first Thank you everyone for answering my question. I tried all of your techniques then understood that the problem is with the DCPIP salt, maybe expired or something else. So I ordered a new bottle and it dissolved in distilled water easily yesterday and added in the media for degradation test. Now waiting to see my results.

Hopefully, I will be able to do my biodegradation assay perfectly.

Again thanks .

@Sumona Akter

Good to hear that..

Good luck with your results

Plz can i ask for the optimum concentration of the indicator DCPIP to be used in biodegradation assay

Nehal Khairy you can use 1g/L DCPIP or 0.1% DCPIP